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Section 3: Wood products and their use in construction


ALAN D. FREAS IS chief of the Solid Wood Products Research, Forest Products Laboratory, Forest Service, U.S. Department of Agriculture, Madison, Wisconsin, United States. This paper is based largely on the background papers, which are listed at the end, and acknowledgement is made to their authors.

WOOD IN SOME FORM has always been a primary housing construction material. Once man left the natural shelter of caves and began to build his own shelter where he wanted it, the most universally available material was, usually, wood.

The nature of wood use has, of course, varied from region to region and changed with time. Log structures have been common in many areas; and sapling-size supports for coverings of hide, cloth or leaves have been used by many different cultures, particularly nomads, because of easy transportability.

AS man has developed, so has his use of wood for shelter. Modern man in some areas still uses a great deal of wood in housing, but he now has it available in a variety of forms which have resulted from technological advances. He has, further, a considerable scientific background which permits greater structural efficiency, and more effective protection from heat and cold, and from destructive elements such as fire, fungi, insects and weather.

The objective of this paper is to provide a broad-scale review of the modern use of wood as a basis from which adaptations can be made to fit conditions in any specific area.


For one reason or another, the extent of wood use varies greatly from area to area. Blomquist (15), in a paper prepared for a conference sponsored by the United Nations Industrial Development Organization, speculated on some of these reasons.

He points out that in many countries there is considerable concern over the possibility of fungi and insect attack, and that not all wood species are resistant to such attack. Treatment with preservatives and the incorporation of special design features can reduce the hazard, but the facilities (and knowledge) for using these preservatives are not always available. The use of open fires for cooking and heating in some areas introduces a fire hazard which is a deterrent.

Blomquist points out also that, while many developing countries have a liberal supply of timber, a commonly serious lack of knowledge of timber characteristics creates problems in the choice of species and in their application.

Not mentioned by Blomquist, but undoubtedly a factor, is the matter of tradition. In many instances masonry is the accepted material for housing and the use of wood is looked on with more or less disfavour. These and other aspects which tend to militate against the use of wood are treated in detail in Section 4.


The extent of wood use in housing varies substantially from area to area. Wood houses are probably far more common in Canada and the United States than in any comparable area. House construction practices in these countries have thus been drawn on heavily in the preparation of this paper.

Canadian and United States methods may not be directly applicable in other areas. They do, however, cover a variety of climatic conditions and provide a base for adaptation to specific areas, and this section reviews successful techniques in the use of wood and wood-based materials in these countries.

In the United States, an average of I to 1.5 million new housing units are built each year. While an increasing proportion are apartment units-both high- and low-rise-more than half are single-family houses. Most of these are wood-framed, as are many of the low-rise apartment units. A good share are site-built; that is, most elements are assembled at the housing site. An increasing percentage, however, utilizes prefabrication to some degree. Even with site-built units, for example, the use of prefabricated roof trusses is becoming more common.

Factory-built housing units are likewise becoming increasingly important. One recent estimate was that nearly half of the units to be built annually will soon be factory-built, with a substantial portion of these in the form of mobile homes. The use of modular (three-dimensional) units is limited because of problems in transportation and erection. The closest approach to this is the use of half-width mobile homes which are joined at the site.

A report by the U.S. Forest Service (17) indicates the magnitude the market for wood products represented by residential construction. The report points out that construction activities account for about three quarters of the lumber and plywood consumed annually in the United States. Not all of this, of course, is used in residential construction, but about three quarters of the construction lumber is used in new construction or in maintenance of residential units, together with about half of the plywood and substantial volumes of fibreboard, hardboard, and particle board.

Total use in 1962 and estimates for 1970 are:




Million board feet

13 960

14 390

Million cubic metres



Plywood (3/8-inch basis)

Million square feet

4 170

5 250

Million cubic metres



Building board (insulation board, hardboard, particle board)

Million square feet

1 650

1 990

The typical home in the United States has a supporting framework (floor, roof and wall) of lumber nominally 2 inches thick, commonly called "dimension" lumber. The framing accounts for about two thirds of this lumber, the rest going to flooring, exterior covering and the like. Only about one house in ten in 196X had masonry walls, the rest being wood-frame (25).

Lumber use in certain applications is being largely superseded by panel products. For example, subfloors and wall and roof sheathing were usually built of lumber in the past, but plywood is now used increasingly for subfloors and roof sheathing, and plywood or fibreboard for wall sheathing.

Exterior surfaces in wood, usually bevelled siding (lumber), were typical until recent years. Other wood materials, including plywood and hardboard, are becoming more important, but nonwood materials now fill a fairly large proportion of the market.

Hardwood strip flooring accounts for about half the floor surface material. The use of other materials, including flexible tile and carpeting, is growing, particularly in houses built on a concrete slab.

Particle board utilization is increasing, particularly as underlay for flexible flooring and carpets and as the core for countertops and cabinets.

The typical roof covering in the United States is the asphalt shingle, largely because it enjoys an advantage in fire endurance ratings.' Asphalt shingles are, in large part, wood, since the felt from which they are made is wood-based. Wood shingles and shakes are used to some degree, and increased use may be expected as improved methods for imparting fire resistance are developed.

Wood-frame construction in the United States is described in detail in a handbook by Anderson (10). It presents basic principles of wood-frame house construction and is designed to serve as a guide for those without experience. It is profusely illustrated.


A number of recent developments in the field of housing at the U.S. Forest Products Laboratory are described briefly here, with details covered in the references.

Nu-Frame house. The U.S. Forest Products Laboratory continually searches for new ways to utilize wood and wood-based materials with greater structural efficiency. At times, houses or other structures have been erected to demonstrate the performance potential of these concepts. Very recently the Nu-Frame concept was developed as the result of research objectives to answer diverse problems: too many low-grade boards remained unused; costs of labour for on-site construction were rising rapidly; enclosing a house required too many different operations and was too time-consuming; pre-finished or dual-purpose components could have construction advantages; adhesives might provide added rigidity and ease of construction.

This unique framing system is based on five components, illustrated in Figure 1. The wall-framing system utilizes low-grade 2- by 4-inch studs set flatwise on either side of a fibreboard diaphragm, which serves as a stiffener and as a heat and sound insulator. An interior wall surface component utilizes foil-back gypsum board. Because the unit is intended to span 4 feet, it is reinforced by 1-inch boards bonded to the gypsum panel. A third component, the truss, is designed to be installed at 4-foot intervals. The construction offers distinct advantages in manufacture and transportation. The exterior coverings for wall and roof are combinations of materials so designed as to require only a single layer, rather than the two normally used.

The Nu-Frame system bonds a considerable amount of surfacing material, exterior and interior, with mastic adhesives. This greatly reduces the number of mechanical fastenings (mainly nails) required for erection. A prototype house, erected on the Forest Products Laboratory grounds, required only about 5 800 mechanical fasteners compared with the more than 30 000 used in conventional construction. Anderson (8) describes the development of the system and construction of the prototype.

Low-cost house designs. In response to a demand for economical but sound homes to help alleviate the nation's housing crisis for low-income families, the Forest Service developed a series of plans for houses of varying style and size. They have all the essentials for families with up to 12 children and are intended primarily for rural situations. These designs are described briefly in Designs for low-cost wood homes (12).

Savings have been made through simplicity of design, by specifying economical but durable wood materials, and by employing unconventional new materials, systems and uses of wood and wood products. The fact that these homes are low-cost does not mean that they use second-rate materials or construction methods. Strength, safety and durability have not been sacrificed.

In many cases, construction and materials are conventional. Thus they can be built by a small contractor using readily available materials. In many cases, too, the owner will want to do some of the work himself. Accordingly, a well-illustrated manual has been prepared to assist the contractor or home-owner. This publication is Low-cost wood homes for rural America: construction manual (9).


Information on wood for housing in developing countries is difficult to obtain. Blomquist (15) has summarized information from a few areas which suggests that wood use is not well developed.

In Papua and New Guinea, for example, typical native housing is based on vertical posts or poles with floor and roof framing, usually of round members fitted to flat surfaces on the poles and attached by vines or similar fastenings. Thus it is similar to North American pole-framing systems. In some cases a truss of round members, occasionally sawn timbers, is used for the roof support. Small round timbers span the trusses, with thatch or other natural materials used for roof covering. Bamboo or similar material may be used for wall enclosures.

Sawn lumber may be used for door and window closures.

Typical construction in the Philippines uses the post-and-beam method, with pole-type constructions used in some instances. Roof trusses are usually wood with steel members used to carry tension loads. Wood roof trusses joined with nails or with metal connector plates are being introduced. Some wood flooring is used and exterior wood wall coverings are becoming more popular. Interior coverings are commonly fibreboard and plywood, and prefabricated wood-frame windows are widely used.

South Africa uses relatively little wood in housing, but developments by the Timber Research Unit of the South African Council for Scientific and Industrial Research indicate a possible increase in wood use. A recent design by the Timber Unit incorporates preservative-treated lumber framing, together with wood siding.

In India it appears that houses generally have masonry walls and nonwood floors, but wood roof systems are well developed. The Forest Research Institute has developed a series of truss systems which utilize the smaller pieces of secondary native species, to reduce reliance on the four to six most popular structural species.

Use of sawn lumber

Early housing in North America was built of logs, but the introduction of sawmills meant that logs could be cut into lumber. Thereafter, the abundant supply of timber and the relative ease with which it could be converted made the lumber frame house with wood sheathing the standard for home construction in North America. This type of construction, with modifications resulting from the introduction of new materials such as plywood and fibreboard, remains the most common today.

FIGURE 1. - Specific components of the Nu-Frame system: A, wall framing;

FIGURE 2. - Specific components of the Nu-Frame system: B. interior wall covering

FIGURE 3. - Specific components of the Nu-Frame system: C, dual-chord W-truss

FIGURE 4. - Specific components of the Nu-Frame system: D, exterior siding; and

FIGURE 5. - Specific components of the Nu-Frame system: E, plastic plank roof covering.


The most important lumber item in house construction is called "dimension," used basically for the house frame. It is generally 2 inches in nominal thickness, with various widths to suit its use as a stud, floor joist, roof rafter, and so on.

Boards, generally of nominal l-inch thickness, are now little used except in some items of trim such as soffits, corner boards and porches. They also furnish the raw material for patterned lumber for moulding, siding and exterior trim.

The basic descriptions of various lumber items are given in the American softwood lumber standard (30). This standard sets limits on finished sizes, moisture content, basic grading characteristics and methods of arriving at working stresses and modulus of elasticity values. Detailed grade descriptions are given in grading rules issued by regional lumber associations.


A method called "balloon framing" has been used to some extent. In this type of construction, the wall studs are continuous from Sin to eaves. Joists for the second floor are supported on a ribbon strip let into the inside edges of the studs. This construction minimizes changes in dimension over the height of the wall and thus is preferred where the exterior covering is masonry.

A more common type of construction is called "platform framing" (Figure 2), where the subfloor extends to the outside edges of the building and provides a platform on which exterior walls and interior partitions are built. This is easier to erect in that it provides a surface at each floor level on which to work. It is adaptable to various methods of prefabrication and enables the wall framing to be assembled on the floor and tilted into place.

An adaptation of the heavy timber system which is sometimes used in residential construction is the "plank and beam" method (Figure 3). Beams of adequate size are supported on posts spaced up to 8 feet apart and covered with planks or tongue and groove decking.

FIGURE 2. - Typical platform framing.


House frame

The conventional house frame uses nominal 2-inch dimension for sills, plates, headers, joists, studs, and rafters or trussed rafters. The floor consists of floor joists, of a width determined by the span, and supported on the foundation and on an intermediate beam. The joists are covered with subflooring to provide a working platform for further construction.

Walls are generally built of 2- by 4-inch studs attached to a sill at floor level and to an upper plate. Supports at openings for windows and doors are provided by a header (usually nominal 2-inch dimension of appropriate width).

Roof framing has commonly consisted of roof rafters supported at the walls and joined at the centre to a ridge board (Figure 4). The rafters are nailed to the ceiling joists. This construction is now often supplanted by light trusses (trussed rafters) made from dimension lumber. The use of trussed rafters simplifies construction since they can be set in place as a unit and do not require interior walls to support the ceiling joists.


Wall and roof sheathing and subfloors are intended to stiffen the walls and to provide a nailing base for the coverings. In the past, sheathing commonly consisted of 1-inch boards applied either diagonally or at right angles to the framing members. When diagonally applied, board sheathing imparts considerable stiffness and thus resistance to hurricane and earthquake forces.

Following the second world war, panel products of structural plywood and fibreboard began to replace lumber sheathing and subflooring. Now a typical house consists of a sawn lumber frame with plywood roof sheathing and subflooring and with wall sheathing of fibreboard or a combination of fibreboard and plywood.

Finish carpentry

Although style changes have eliminated or reduced some items of wood finish, sawn lumber is still used extensively for exterior and interior trim, finish carpentry and flooring. Among these are fascia, soffits, trim, corn" boards, porches, decks and wood siding.

Probably no other siding material is available in the variety of patterns and textures in which sawn lumber is regularly produced. Horizontal bevel siding is perhaps the most common, but other patterns for both horizontal and vertical application are available.

Latest statistics (25) indicate that the use of lumber siding (in houses insured by the Federal Housing Administration) had declined from approximately 12 percent in 1959 to 5 percent in 1968, with increases shown for plywood, fibreboard and nonwood sidings. Continued improvement in exterior finishes may reverse this trend.

FIGURE 3. - Plank and bean framing for one-storey house.

Wood roofing

Asphalt shingles are by far the most common roof covering in the United States. Available statistics indicate only a limited use of sawn shingles and split shakes. Development of suitable fire-retardant treatments may result in increased use of wood shingles. Not only do wood shingles and shakes have an important aesthetic appeal, but they offer better insulating qualities and thus reduce heating and am-conditioning costs.


Only a minor amount of sawn lumber is now used in panelling. The lower cost and greater ease of handling and application of plywood account for this change. Provision of sawn panelling in lesser thicknesses than the standard 3/4-inch and in greater widths may increase its application.

Millwork and flooring

Sawn lumber provides the basic raw material for windows, cabinets, and flooring. For these uses wood continues to maintain its position considerably, except that resilient tile and carpeting are becoming popular as flooring materials at its expense. Observations on the use of wood in millwork and flooring are given on page 65.


Lumber sizes

History suggests that cross-sectional dimensions of sawn lumber for use in house construction evolved from the sawing and resawing of cants into even-inch increments. Finished sizes have gone through considerable evolution with respect to the nominal sizes, with the latest American softwood lumber standard (30) being the first to deal explicitly with the problem of shrinkage from surfaced-green dimensions to those which prevail after some period in service. That is, they specify finished dimensions for both surfaced-green and surfaced-dry material. Comparison of former 2-inch framing lumber sizes with new PS 20-70 dimensions can be summarized as follows (measurements in inches):

Nominal reference

Former sizes, green or dry

New sizes PS 20-70 19% m.c.

2 × 4

1 5/8 × 3 5/8

1 1/2 × 3 1/2

2 × 6

1 5/8 × 5 1/2

1 1/2 × 5 1/2

2 × 8

1 5/8 × 71/2

1 1/2 × 7 1/4.

2 × 10

1 5/8 × 9 1/2

1 1/2 × 9 1/4

2 × 12

1 5/8 × 111/2

11/2 × 11 1/4.

Working stresses

The current softwood lumber standard specifies that where working (design) stresses are to be assigned, they shall be developed in accordance with technically adequate standards. Principal among these are Standards D 2555 and D 245 of the American Society for Testing and Materials. These are constantly under review.

FIGURE 4.- Typical rafter framing.

Design criteria

Design criteria in terms of floor, sidewall and roof loads referenced in building codes and construction standards have sometimes been regarded as constraints to the more efficient use of wood framing in house construction. That is, they have been considered unduly conservative in relation to methods of structural analysis. Full-scale tests have indicated performance superior to that assumed under current design criteria (19). On this basis, representatives of the four model building codes in the United States (the Federal Housing Administration, the National Association of Home Builders, and the forest products industries), met and developed new and uniform design criteria. These criteria, which are shown in Table l, have been incorporated into the new National Building Code for One- and Two-family Dwellings and into standards of the Federal Housing Administration. Simplified span tables based on the new criteria are available.


Structural assembly


Live load²

Dead load

Total load

Pounds per square foot

Floors - heavy





Floors - light³





Ceiling joists
Limited attic storage





Ceiling joists
No attic storage





Low slope roof joists
Supporting ceiling4





5 (30)






Low slope roof joists
Not supporting ceiling











Rafters - heavy roof











Rafters - light roof











¹ Spans divided by number shown. For plaster ceilings divided by 360 throughout. - 2 Live load used only in computing spans based on deflection.-3 Attic floors and sleeping rooms. - 4. Also rafters supporting ceiling.-5 Loads in parentheses are alternate loadings to accommodate climatic conditions.

Modular coordination

A development in modular coordination for the more effective use of wood is the Unicom system developed from studies sponsored by the National Forest Products Association. Using the 4-inch module and the 16- or 24-inch spacing, the house designer has complete design flexibility and the builder or component manufacturer uses standard materials with minimum waste. In addition to the saving from a standardized design and fabrication discipline, the system also eliminates bridging between floor joists, doubling of headers under parallel partitions, blocking between studs, and other features which contribute little structurally. In two housing projects analysed, it has been reported that use of the Unicom system resulted in savings of U.S.$63 000 for one (250-house) project and $20 600 for the other (23).

Low-profile floor system

The increasing use of concrete slab foundations, which began in the early 1950s and has stabilized over the past 10 years at about 43 percent of all single-family houses, resulted in a significant reduction in the volume of lumber and related wood products used for floor construction.

Conventional wood floor construction over a crawl space places the floor level well above the exterior grade. To combine the advantage of the low silhouette, the lower construction costs of the concrete slab and the comfort and appearance of a wood floor, a low-profile floor system was developed (22). This low-profile system permits shorter spans of smaller size lumber through intermediate supports. It also utilizes the narrow under-floor space as a plenum chamber for heating and air-conditioning. This floor system provides a workable solution in wood for those areas where builder and consumer preference dictates a low house silhouette.

All-weather wood foundation

Weather is one of the problems frequently cited by builders in explaining increasing construction costs. In many areas of the country, adverse weather conditions make it difficult or impossible to excavate and construct conventional masonry foundations. A new all-weather wood foundation system has been developed to overcome this problem. This system is the product of a three-year effort by the National Association of Home Builders Research Foundation, the Federal Housing Administration, the Forest Products Marketing Branch of the Forest Service, the American Wood Preservers Institute, and the National Forest Products Association. It can be erected in 9 man-hours, at a saving of $250 per house compared with the conventional masonry foundation (7).

The all-weather wood foundation system consists of a wood frame with plywood-sheathed panels pressure-treated against termites and decay. It provides for fully insulated below-ground habitation and enables the industrialized home builder to provide a complete house package which can be totally assembled by carpenters.

This system and its low-profile counterpart overcome major deficiencies in conventional foundation construction for low- and middle-income housing


Conventional wood-frame house construction has remained essentially unchanged for centuries. The widespread adoption of the trussed rafter and panel sheathing products is the only significant modification of the standard system of joists, studs and rafters covered by sheathing and siding.

Since the wood frame has proved adaptable to industrialized construction, it seems unlikely that the trend to factory fabrication will substantially modify the sheathed frame system. This appears to be borne out by the fact that new steel and aluminium house frames have copied the wood system.

Factory fabrication and the increasing trend toward building with three-dimensional modules should place greater emphasis on weight reduction in the house frame. With its favourable ratio of strength to weight, sawn lumber can be more adaptable to such efforts than the metal frames.

Although reductions have been made in the standard dimensions of wood members, these changes were based upon each member acting independently. However, full-scale performance testing has revealed that interaction of members and sheathing in the completed house adds significantly to the strength and rigidity of the system. Efforts to develop a reliable design procedure to reflect such interaction are presently under way. Such a design technique, in combination with improved fastenings and structural adhesives, should make further economies in the wood-frame system possible.

While sawn lumber for sheathing purposes will continue to decline in use, development of a composite design procedure and better fastening methods may well lead to new and more efficient uses of board lumber for structural frame applications.

Use of poles and posts

A building system increasing in popularity for house construction uses preservative-treated wood poles as the foundation and the structural framework (Figure 5). While round poles are generally used, sawn timbers are occasionally employed. In either case, they are embedded in the earth and serve as the principal supporting elements of the structure. Thus the poles serve two basic functions-that of the foundation and of the framework supporting the floor members, the walls and the roof framing.

Conventional foundations are not required, so that there is less site preparation and, more important, less soil disturbance and a reduced possibility of erosion. The lack of soil disturbance also reduces the possibility of extensive soil movement on steep slopes. This system is thus more adaptable to rough topography than constructions with conventional foundations. With the poles properly embedded in the earth, and with adequate joining of all elements, this type of construction is especially effective in resisting major structural damage in high-wind areas, including those where wave action may accompany high winds (2, 5, 11, 26).


Pole construction depends upon the ability of the poles to resist deterioration from wood-destroying organisms, such as fungi and insects in the soil in which they are embedded. Since the sapwood of even resistant wood species has little durability, this implies that poles must be preservatively treated to ensure long life.

FIGURE 5. - Pole construction has been used successfully in reducing the cost of housing. It is especially adaptable to steep hillsides and rough terrain.

Round poles are most common in house construction, although rectangular members are sometimes used for simplicity in framing. Rectangular members require greater care in treatment, because frequently the sapwood is partially or completely removed and the heart-wood of many species is difficult to treat.

The treatment of wood to protect it from wood-destroying organisms is well developed, and chemicals and treatment processes are well known and described in a variety of references, including (4) and (7). It is beyond the scope of this paper to describe chemicals and processes in detail. Pressure processes are most common, although other processes may be used. The choice of preservative chemical rests on a variety of factors, but paintability, freedom from odour, as well as permanence and effectiveness, are important factors. Government regulations may, in some areas, limit or prohibit their use and such regulations should be consulted before making a choice.


The design of a pole house entails nothing unusual, except for considerations related to soil characteristics affecting depth of pole embedment, and soil-bearing strength. In areas of hurricane hazard, special attention must be paid to the connexions between elements, and between the various elements and the poles. Design features are covered in (4) and (5).



One of the advantages of pole construction on sloping sites is the reduced likelihood of erosion, as compared with foundations which require extensive excavation. The preparation of the holes for pole embedment, however, still requires care to avoid soil disturbance. While the holes can be dug by hand, machine drilling is much faster if equipment is available and if the site permits it.

Figure 6 illustrates several methods of pole embedment. In certain types of soils, backfilling with the original soil is satisfactory. Where this is not feasible because of lack of adequate support, backfilling may be done with sand or gravel or with soil-cement mixture. The latter may be especially important in developing countries where self-help methods would be convenient.

FIGURE 6. - Pole placement - soil type and topography will generally dictate the method of pole embedment.

Where the bearing strength of the soil is inadequate to support the imposed loads, it may be necessary to provide a concrete pad at the bottom of the hole to provide greater bearing area than would result from the base of the pole alone. Pads may be poured in place or precast and placed in the base of the holes. Backfilling can be as suggested earlier or, for shallow holes or for certain soil types, it may be desirable to backfill around the poles with concrete.

Before backfilling it is necessary to position the poles exactly and to plumb them. It may be desirable to attach some of the framing and square and plumb the whole structure before backfilling, particularly if concrete is used.

Support beams

Three common attachment systems for support beams are shown in Figure 7. Bolts or spiked grids are commonly used in connecting floor beams to poles because of the higher loads imposed by floors, while nails may be suitable for attaching roof beams. Design data for connexions are given in (24) and (29).

FIGURE 7. - Three methods of attaching beams to the poles.

Sawn beams for supporting floor joists and wall framing are attached to the poles as indicated in Figure 8. Where joists are used, or where poles are cut off at floor level, the beams must also be designed to carry roof loads transmitted through the wall framing. Normally, however. roof framing is supported on roof beams at the top of the poles.

Good practice suggests that the support beams be attached in pairs, one on each side of the pole. Where. as is frequently the case, floor support beams are exposed to weather, it is best that they be treated with a preservative.

Wall and floor frame

Conventional framing is common. In general, however, floor joists are positioned on top of the floor support beams, which creates some problems in attachment. While toenailing may be satisfactory in many instances, special joist connexions (Figure 8) are recommended where wind loads are high (26).

Wall framing is usually placed inside the pole line to simplify construction, leaving the poles exposed (see Figure 5). Occasionally the design calls for the poles to be fully or partially exposed inside the house. This complicates final framing and finishing and may add substantially to labour costs.

Roof frame

Three general types of roof frame are encountered in pole construction. The first, which might be called " post and beam," requires a line of poles down the centreline of the house to support ridge beams to which the rafters are attached. A different arrangement would still require a line of poles down the centre of the house but would utilize large-dimension rafters, more widely spaced, to which purlins would be attached. More commonly, conventional rafter construction or trussed rafters are used.


Short posts are used to some degree in house construction, terminating at first-floor level, with floor beams attached to their upper ends. Such posts may be set as described earlier for poles. Within the past few years. however, a technique has been developed for driving highway guardrail posts (18), and this technique could be used for embedding foundation posts for houses.

Glued and composite elements

A glued wood element may be considered an assembly of parts (primarily wood) bonded together by an adhesive to serve a particular structural function. For example. a stressed-skin wall of floor panel, consisting of plywood facings bonded to lumber framing, would fit such a definition, as would a glued-laminated wood beam. For this discussion, a composite element is considered to fit the same definition except that some parts may be of a material other than wood. For example, a sandwich panel could consist of plywood facings with paper honeycomb or plastic foam core.

Such elements have had some use in construction for three decades or so. Experience has shown that factory fabrication is nearly always required to ensure proper control of dimensions, proper curing of the adhesive, and so on.

A growing number of wood-frame buildings use prefabricated elements such as roof trusses. The majority of these have been assembled with mechanical fastenings, but adhesives are now being used increasingly.

Glued elements are used, for example, for box beams used as clear-span floor beams or as ridge or roof frame beams (often exposed for appearance), or as lintels over openings in walls. Stressed-skin and sandwich panels have been used for floors, walls and roofs in place of more conventional construction.



A glued prefabricated element offers certain advantages over conventional construction, primarily increased speed of construction as labour requirements are reduced on the site. Construction speed may also be enhanced by reducing delays due to weather.

Shop fabrication can result in higher quality components, with better control over moisture content and thus dimensions of individual parts. Closer control of element size may also result in more efficient use of materials.

Thermal insulation can be built in during shop fabrication; in foam-core sandwich panels it is an integral part of the assembly. Similarly, electrical, plumbing and mechanical systems can be built in.

Many of these advantages of prefabrication apply also to nonglued elements. Glueing, however, generally develops a greater proportion of the structural potential and can give a permanently tight joint.


Glued prefabrication also has limitations. For example, considerable investment in manufacturing facilities and organization is required. This is justified only when requirements of a substantial volume are foreseen. When one considers transportation and erection costs for prefabricated elements, cost in place may be greater than for an equivalent unit built on site. Individual instances differ so greatly, however, that no general statement can be made and each case should be analysed separately.

Unconventional or nonstandard elements generally require special structural and architectural attention. Building code acceptance may be a problem.

Elements built off-site require careful coordination with the builders who will assemble them at the site, as well as control of dimensions to ensure fit after they arrive.

FIGURE 8.- Continuous pole and truss construction with platform framing


A number of elements are used primarily in engineered light-frame construction, although they find some place in ordinary residential construction. These include glued-laminated timbers, plywood box beams, trusses, stressed-skin panels and sandwich panels.

Glued-laminated timbers

Glued-laminated timbers are made up of layers of lumber, the grain direction of each layer parallel to the long dimension of the member, bonded with a rigid adhesive. They can be made either straight or curved and of any length or cross section.

These versatile members find some use in residential construction as long-span floor or roof beams. In general, though, they are limited to relatively high-cost residences.

Plywood box beams

These box beams consist of a top and bottom lumber flange, either solid or laminated, connected with one or more vertical plywood webs, usually glued to the flanges. Such members are lighter in weight and more efficient than solid lumber, as well as being more stable dimensionally.

They are used occasionally for floor and roof framing, and sometimes in small dimensions to span openings such as windows or garage doors.


Trussed rafters are commonly used in house construction in the United States. They are generally at conventional spacings-16 or 24 inches-and roof and ceiling panels are attached directly to them. Usually they are made of 2-inch dimension lumber with the truss members joined with metal plates, although glued gusset plates are also used. Trusses having large, rigidly glued plywood gusset plates are substantially stiffer than those made with light metal plates because the joints resist rotation of the truss members.

Most trusses do not have space for storage in the attic of the completed house. With proper design, however, this can be provided.

Stressed-skin panels

A stressed-skin panel consists of a covering glued to one or both sides of framing members so that all parts act integrally. The coverings resist flexural and direct stresses, thus adding to the load-carrying capacity of the framing and permitting a reduction in its size. The framing resists shear as well as flexural forces. Attaching the skins to the framing with adhesive is the most effective system, although mechanical fastening may be used.

Panel skins may be on one or both sides of the framing. One-sided panels facilitate installation of utilities. Two-sided panels, however, are more efficient, because both skins contribute to load-carrying capacity.

Stressed-skin panels may have blanket insulation installed at the factory. Because of their otherwise tight construction, it is common practice to provide vents by notching or drilling end headers. Special means for connecting panels on the job must be provided. This is usually done by setting out the framing at one side of the panel and nailing it through the projecting skin of the adjacent panel.

Wall panels are generally 4 by 8 feet in size with floor panels 4 feet wide but 12 to 14 feet long. Such panels are light enough to be handled manually. With the advent of on-the-job handling equipment, larger sizes have been used. Wall panels, for example, may be full length, while floor panels may be shop-fabricated in sizes up to 8 by 28 feet.

Sandwich panels

A sandwich panel is similar to a stressed-skin panel in that skins act together with a lightweight core to resist loads. However, instead of a spaced framework, the core is essentially continuous, such as foamed plastic or paper honeycomb. Skins can be thinner than for a stressed-skin panel because they have more continuous support. A variety of materials may be used including wood-based materials such as plywood and hardboard skins and paper honeycomb cores. Frequently, wood strips are glued to the perimeters to strengthen the core and to facilitate attachment to adjacent panels.

A sandwich panel is lighter in weight than a stressed-skin panel, and the foam-core panels are better insulators. Sandwich panels generally cost more and must be prefabricated.

There are a number of proprietary systems of wall. floor and roof panels currently in use, generally in 4-foot widths. Wall panels use foam cores from 11/2 inches thick, while roof and floor panels are generally 4 to 6 inches thick, depending on span. House systems have been produced with whole walls 8 by 20 feet or more in size.

Three-dimensional units

Complete residential units may be assembled at the factory and may employ one or more of the glued elements described earlier. Typical units are mobile homes and modular structures.

Mobile homes are self-contained, box-shaped residential units on a wheeled undercarriage. Many units are moved only once-from the factory to a site. In some instances they need not comply with established building code regulations. They are produced on an assembly line. The method of construction varies, but one common feature is the frequent use of adhesives for assembly.

Modular structures are box-shaped units which can be transported on a trailer and set on foundations to form part of a permanent structure. They are often sectionalized. Two or more units may be joined side by side, with one side of each section open, or fully enclosed units may be joined horizontally in various configurations. The fully enclosed units may also be stacked one on the other or in a separately built frame.

Transportation and erection loads impose stresses not normally encountered in house construction. The increased rigidity provided by glued elements is essential to resist such dynamic stresses.


Structural bonding with adhesives on the site, not easy or practical in the past because of work and weather limitations, is now possible thanks to a new class of adhesives. These elastomeric adhesives come ready to use and are easy to apply. They fill gaps and do not require extra sanding of commercially produced surfaces. They set with only moderate pressure and will quickly withstand impact construction loads without breaking. They are relatively tolerant of weather conditions and can be applied to wet or frosty surfaces over a range of temperature conditions. They are not, however, recommended for use under severe exposure conditions. A main limitation is their tendency to creep under load.

The elastomeric adhesive is coming into common use for attaching plywood floors to joists. This gives partial stressed-skin action and the system is stiffened. Nailing problems are minimized, since the adhesive holds the panels tight to the joists. Thus, field glueing combines many of the advantages of shop fabrication with those of field construction. Other applications could include attachment of wall or roof sheathing to the frame. This has been done experimentally with the Nu-Frame system described earlier.


Recognized design methods exist for the elements discussed earlier (1). When these elements are assembled in a building, the structure can be analysed for resistance to horizontal forces, such as those resulting from hurricanes and earthquakes.

Wood structures are recognized as being outstanding in their resistance to earthquakes and, with proper anchorage and connexions, to high winds. The glued elements described here add to this capacity.

Fire performance of wood structures can be improved in various ways. Fire-resistant components can be incorporated into a composite element. As an example, a stressed-skin floor-ceiling panel has been tested and rated as " one-hour fire resistant." It consists of 2- by 6-inch joists with 5/8-inch top skin (floor) glued to them, while the ceiling is a layer of 1/2-inch fibreboard covered with 1/2-inch gypsum board.

Treatment with fire-retardant chemicals can drastically reduce the rate of surface flame spread, but has little effect on fire resistance. However, such treatment, combined with suitable construction features, can improve the fire performance of wood structures.

Panel products

Income has an important effect on what materials are used for housing; where incomes are low, housing is minimal also. Wood-based panel products, the results of improving technology, are relative latecomers in the field of building materials. Because plants needed to produce them require considerable capital investment and highly skilled labour and technology, they find most use in the more developed and affluent areas of the world. About 75 percent of world production of plywood, insulation board, hardboard, particle board, and panel products of lesser volume, is used in the United States and Europe.

The main uses for wood-based panel products are in construction. As a group, they have shown a phenomenal growth since the second world war. There are significant reasons for this which suggest that further growth in consumption may be expected if the world's housing needs are to be met. These include:

Maintaining a reasonable ratio of labour to material costs. The costs for fixing panel products in place are less per unit area. With increasing labour costs, this factor becomes increasingly important, for it is cost in place rather than material cost that should govern choice of material.

Panel products are frequently developed for specific uses. The panel products industry has a number of products developed for specific uses in housing.

Elimination of "wet-wall" construction. Past practice has been to plaster interior wall surfaces. There is now a transition to " dry-wall" construction which opens the way to increasing use of all types of panel products for interior surfaces.

Development of factory fabrication of housing. Increasing prefabrication of housing elements and mobile homes takes advantage of the characteristics of panel products. While the 4- by 8-foot size is common in on-site construction because of the ease with which it can be handled, larger sizes can be used in factories where mechanical handling is possible. Panel products withstand transportation and erection stresses better.

Prefinishing and special surfaces. Factory-applied finishes and special surfaces not only provide attractive and durable finishes but reduce on-site labour. Special methods are needed for attaching prefinished panels.

Code regulations frequently limit or prohibit the use of combustible materials in high-rise housing. These limitations apply to wood-based panel products as well as to lumber. Some use of panel products for nonstructural purposes may be permitted, but fire-retardant treatment is generally required. Restrictions on wood use are often less in single-family housing.


The construction plywood industry is concentrated in four main areas: North America, with softwood plywood; Finland, with birch plywood, and its developing spruce-core, birch-face plywood; Australia, with radiata pine; and Japan, with both lauan and American softwood. France uses tropical and other hardwood plywood and the United Kingdom substantial amounts of both Finnish and British Columbian plywood.

Construction plywood is used considerably for concrete forms because it provides a smooth surface and may be used again. For repeated use, plywood with a high-density overlay is desirable.


Some use is being made of plywood for foundations, and this is likely to expand. Preservative treatment is necessary.

Floor systems

Plywood is commonly used as the subfloor in housing. Thicknesses of 5/e to 3/4 inch are generally used on usual joint spacings. Thicker plywood is required for greater spans, as in post and beam construction.

Wall sheathing and exterior covering

The major functions of wall sheathing are to prevent air infiltration and to provide racking resistance. Properly fastened plywood provides excellent racking resistance. In some instances, part plywood sheathing and part fibreboard are used.

Plywood is used increasingly for siding (cladding). It is frequently applied vertically, sometimes with grooves or other working for appearance. It is supplied in 12-inch-wide strips for horizontal application as lapped siding It is sometimes applied in full panels as a combination sheathing and siding When this is done the nailing must be frequent to furnish the desired racking resistance, and this may detract from appearance.

Roof sheathing

In North America plywood is the most frequently used roof-sheathing material. Sheathing grades in thicknesses of 3/8 or 1/2 inch are commonly used for spans up to 24 inches, a common spacing for roof trusses. As for subfloors, greater thicknesses are required for wider spacing as in post and beam construction.

Miscellaneous uses

Considerable amounts of plywood are used for incidental purposes in housing, such as soffits and returns at roof edges; shelving; porch and carport ceilings; and miscellaneous built-ins.


Decorative plywood is used in panelling and for the skins of flush doors. The mobile home industry uses substantial amounts of decorative plywood for interior surfaces. Kitchen cabinets and other built-in items are commonly made of decorative plywood for appearance.


Laminboard and blackboard are basically European products, used in the same way in construction as thick plywood. Made of thick laminated lumber or vertically laminated veneer core, they appear in 3- and 5-ply configurations between 12 and 25 millimetres (1/2 to 1 inch) in thickness. The grain of the face plies of the 5-ply board may be either parallel or perpendicular to that of the core. Their major uses are in structural flooring, shelving, free-standing partitions and doors or sides in cabinets. They are similar to the lumber-core plywood manufactured in the United States.


Two basic qualities of insulating board are available Ä for interior and exterior use. Water resistance is imparted to the exterior quality by incorporating asphalt in the furnish, by an asphalt coating on the finished board, or both.

The major exterior products are sheathing and shingle backer. Sheathing is made in three qualities and densities: regular, about 18 pounds per cubic foot; intermediate, about 22 pounds per cubic foot; and nail-base, about 25 pounds per cubic foot. Regular density is made in 2- and 4-foot widths, but to provide desired racking resistance the 4-foot width in a 3/,.-inch thickness must be applied with the long dimension (8 or 9 feet) vertical. The two higher densities are supplied only in a l/2-inch thickness. When properly applied, they provide good racking resistance.

Shingle backer is used under coursed wood shingles or sidewalls to provide a deep shadow line. It has the required nail-holding power, when the shingles are applied with special deformed nails, and eliminates the need for wood nailing strips.

Interior-quality insulating board has long been used for acoustical tiles. When holes or fissures are drilled or machined in it, the board absorbs sound and reduces reverberation in a room. Insulating board in tile or board form is usually painted with a fire-retardant paint to reduce the rate of flame spread. Some basic boards are treated with a fire retardant. These find most use in commercial buildings where regulations are restrictive. Increasing emphasis on quiet areas in homes will undoubtedly lead to more use of sound-absorbent boards.

Such boards, however, do not reduce sound transmission in multifamily dwellings. A special sound-deadening board is produced for light-framed construction.

Plain insulating board (undrilled or unmachined for sound absorption) is used in tile form or as lay-in panels for suspended ceilings. It is usually prefinished. It is sometimes overlaid with a washable nonabsorbent film for use in kitchens and bathrooms.


While hardboard has a large number of industrial uses, its main importance lies in housing. A number of these uses parallel those for plywood, where a relatively thin, dense and hard product is needed.

It is used for lining of concrete forms, particularly for curved surfaces, because it can be bent to fairly sharp radii in single curvature. Usually a special quality double-tempered board is provided for this use.

A major use is for prefinished panelling, which is usually provided in the 4- by 8-foot size, either embossed or printed with a wood-grain figure. Prefinished accessory mouldings are commonly furnished with the panels.

Hardboard is also used for floor underlay, where it serves to mask minor irregularities in the subfloor surface and provides a base for resilient floor coverings.

Medium-density hardboard is used mainly for house siding This relatively new product has a density of about 40 pounds per cubic foot and is usually about 3/8-inch thick. It is either primed at the factory or completely prefinished or stained. It may be applied either in panel form or as lapped siding. Where it is furnished prefinished, outside and inside corners and nails are provided in matching colours.

The engineering data for new applications such as skins for stressed-skin panels and gusset plates for trusses are being compiled.

Considerable amounts of hardboard are used as skins for flush doors and as bases for decorative plastic laminates. Properly manufactured hardboard tends to reduce show-through from the base on which it is applied.


Particle board is a relatively new product and uses for it are still developing. There is considerable variation in application in different areas. For example, in the United States relatively little particle board goes into exteriors while in France exterior use is more common.

Particle board may be made by pressing (sometimes classified as mat-formed) or by extrusion. The greatest proportion is mat-formed. Mat-formed particle board is used in Europe not only as core stock for furniture and cabinets, but as wall lining, roof sheathing and finish flooring. The major use in the United States is as floor underlay for resilient coverings, which accounts for some 40 percent of production.

Particle board goes into shelving, concrete form lining (to a limited degree), and core stock. Structural uses such as sheathing and subflooring are uncommon, although recent developments indicate future expansion in this field.

A special product called mobile home decking has been developed for mobile homes. It is somewhat stiffer and stronger than the usual underlay or core stock. When bonded with urea-formaldehyde resin, it is protected from ground moisture and has adequate durability for this use. A similar product bonded with phenolic resin is gaining acceptance for factory-built housing designed for longer life than mobile homes.


In the Philippines, consumption of plywood and hardboard in housing is low, although the industries are well developed. This appears to result from a traditional preference for lumber. It has been reported, however, that corrugated hardboard sometimes replaces corrugated steel for roofing.

The production and use of panel products in Latin America are low, with Brazil producing about half of the total. Brazil is reported to have two large producers of phenolic-bonded plywood for use in concrete forms. Most other plywood produced in the area is for door skins.

Some wood-based panel products go into prefabricated housing in Latin America. For example, it has been reported that several thousand single-storey houses have been constructed of extruded-type particle board in Chile. One company in Colombia has reportedly used hard-board, coated with asphalt, for exterior wall cladding on a thousand low-cost housing units. A large plant in Surinam produces prefabricated houses in the middle-cost range; plywood is used for interior surfaces and particle board for ceilings and built-in furniture.

A particle board manufacturer in Brazil has designed and carried out a pilot project consisting of a thousand prefabricated houses based on elements of phenolic-bonded board. If the first houses are successful, the producer has plans for 15 000 additional units.

Use of wood flooring and millwork in housing


The term millwork is used in North America to designate a group of products including such items as windows, doors and trim. Elsewhere, the term joinery is common. In the United States, however, the terms woodwork and millwork have been used interchangeably. The largest association of millwork manufacturers in the United States carries the title National Woodwork Manufacturers' Association.

The list of items which can be classified as millwork is long. The principal ones from the standpoint of quantity are: mouldings, door frames and entrances, blinds and shutters, sash and window units, doors, stairwork, kitchen cabinets, mantels, and china or corner cabinets.

Millwork has two specific classes: stock and custom. Stock millwork is manufactured in a standard size, pattern and layout ready for use and is available from distributors. Because of standardization it is less expensive than custom millwork. The term stock millwork does not mean monotonous similarity; there is a sufficient variety of sizes and designs to meet a range of demands.

Custom millwork, as the term implies, is made to order to St specific applications. It is sometimes called " architectural woodwork." The principal association of manufacturers of custom millwork in the United States is the Architectural Woodwork Institute. Custom millwork is, of course, more expensive because it is not produced in quantity and requires special manufacturing setups. It is used largely in schools, churches, expensive housing, and public buildings, where it satisfies the requirements of the architectural design.

On the whole, millwork does not serve in a structural capacity in the sense of carrying imposed loads. Stair-work is an exception. Millwork, however, may serve an important protective function, as in window and door units.

It is not practical to attempt to describe here the more common types of millwork, because of the great diversity of items and the variations within each type. A comprehensive review of United States millwork practice lists for sashes and windows alone four principal and seven miscellaneous types (21). Instead, a number of general considerations are discussed.

Species used

The report on a survey conducted by the International Working Group on Timber Information (20) lists some 55 species used for millwork in the 11 countries from which replies were received. The extent of use of individual species, however, was not indicated. It is probable that certain species find only limited, somewhat localized use. The range of species listed is large, including softwoods and hardwoods and both temperate-zone and tropical species.

A paper prepared for presentation at a meeting of the Study Group on Production Techniques in Wooden Houses Under Conditions Prevailing in Developing Countries (14) presents a list of species used for joinery in three tropical areas, covering: Brazil, Paraguay; Congo, Ivory Coast, Kenya, Nigeria; Philippines, Malaysia. This list also gives an indication of use and brief remarks on important characteristics of these species.

Selection of species for millwork will depend on a number of characteristics. Among the more important are: suitability for working with tools; dimensional stability with respect to moisture changes; ease with which it can be dried without serious defects; ease with which it can be fastened (by nailing, for example); natural durability (for exterior use) or ease with which it can be treated; ability to take finishes; and, of course, its availability in sufficient quantity in the necessary quality.


Standards are usually available for the quality of the finished product. These may be prepared by private standard-making bodies, or by or under the sponsorship of a government agency. In the United States, for example, commercial or product standards are prepared by a sponsoring group, subject to the review of a broadly based committee. Coordination is provided by the National Bureau of Standards of the U.S. Department of Commerce.

Besides defining product quality, most standards will also define standard dimensions and describe " standard" products. Standards of dimensioning are needed to promote ease of construction, so that the builder may standardize the framing around window and door openings. Illustrative of a quality standard prepared by an industry association is the book Quality standards of the architectural woodwork industry (13).


The survey mentioned earlier (20) surprisingly indicates that not all exterior millwork is treated to inhibit attack by fungi and insects. It appears, however, that treatment is fairly common, although chemicals may differ.

One of the most common treatments involves the use of pentachlorophenol in an organic solvent, usually mineral spirits. In the United States, the finished product is dipped in the preservative for three to five minutes, and frequently some degree of water repellency is imparted by including a repellent (such as paraffin wax) in the treating solution.

Moisture content

Recommended moisture contents seem to vary considerably. For example, the survey mentioned earlier shows, for products for interior use, recommended moisture contents ranging from as low as 4 percent to as high as 8 to 17 percent. Some of these differences may be accounted for by variations in climatic conditions and in the degree to which homes are heated in cold climates. Apparently, however, a moisture content limitation of some sort is universal.

It is clear that moisture content should be as close as possible to that expected in service. Lacking this, dimensional changes will occur with resultant warping and poor performance.

Use of adhesives

Adhesives are used in a variety of ways in the manufacture of windows, doors, trim and similar items. For example, narrow pieces may be glued edge to edge to provide needed widths. Finger joints are increasingly used for stock of the necessary length. Panel materials such as plywood and hardboard are bonded to the framework of panel-type doors.

Neither of the previously cited references covers this point in detail. It should be obvious, however, that any product destined for exposure to the weather requires the use of a waterproof or, at the very least, a highly water-resistant adhesive if there is any likelihood of free water getting to the glue bond.


Wood flooring is common in housing. A survey of wood use in houses in the United States indicates that, in houses not built on slabs, wood flooring accounted for about 53 percent of the finish flooring used (25). For houses built on a concrete slab, however, only about 5 percent of the finish flooring was of wood (strip, lumber, parquet or plywood parquet).


Wood flooring is made in a variety of types (16, 27), but by far the most common is strip flooring. In 1968, it constituted some 52 percent of the finish flooring of homes inspected by the Federal Housing Administration (25) not built on slabs, while other types of wood flooring amounted to less than 1 percent.

Strip flooring is normally made with tongue and groove on edges and ends to permit blind nailing. A small percentage is square-edged and nailed through the faces. Plank flooring is similar in pattern to strip flooring but is wider. It may be blind-nailed but frequently is fastened with screws, the heads of the screws being recessed and covered with wood plugs.

Block flooring is available in squares in two varieties, unit and laminated. Unit block flooring is made of strips, splined or otherwise fastened together. Laminated block flooring is cross-laminated like plywood and thus shrinks and swells less with moisture change than do other flooring types. The block edges are usually tongue and groove. A variety of special patterns are available.


In the United States, a wood subflooring of boards or, more commonly, of plywood, is used over the joists in nonslab construction. The use of subflooring does not seem to be so widespread in other countries.

As noted earlier, most strip flooring is blind-nailed to the joists, with the flooring length at right angles to the joists. Over concrete slabs, it is usual to lay down sleepers to which the flooring is nailed. Block flooring is also usually nailed. Over concrete slabs, block flooring may be laid in a mastic.

Detailed descriptions of installation practices are given in several references (9, 10, 16, 27).

Species used

Because of its greater hardness and generally greater beauty, hardwood is used for most wood flooring. In the United States, oak, maple, beech, birch and pecan are the most important species (16).

In other areas, a wide variety are used. Suggested species are shown in the two Timber Development Association publications (27) and (28). Selection will be conditioned by stability, tool-working potential and appearance.

Moisture content

Moisture content at the time flooring is laid is important because of the large expanses covered. It should be as close as possible to that expected in service. Too high a moisture content can result in shrinkage and thus the opening of cracks between strips or blocks. Too low a moisture content can result in buckling.

Recommendations on this point vary. In the United Kingdom, for example. recommendations are for somewhat higher moisture content than in the United States. This may well be because of inherent differences in beating practices.

The Timber Development Association suggests 14 percent for buildings heated intermittently and 12 percent for buildings heated continuously (27). United States practice is considerably different, with a suggested average of 7 percent over most of the country, and with averages as high as 11 percent in the damper areas and as low as 6 percent in the drier areas (16).


Standards for flooring are available. In the United States, for example, industry standards are published, and some types of flooring are covered by commercial standards issued by the U.S. Department of Commerce.

Use of adhesives

Adhesives are not commonly used in flooring except for the laminated block type. United States manufacturers tend to use melamine-urea adhesives as a compromise between cost and durability. The type used, however, should be adequate to withstand service conditions.


Wood sealers and varnishes are most commonly used. The former have the advantage of penetrating the wood and not forming a surface coating. Floors finished with sealers are easier to maintain because it is possible to renew the finish in worn areas without going over the entire floor. Factory-prefinished flooring is also available.


(1) AMERICAN PLYWOOD ASSOCIATION. 1966 Plywood design specification. Supplement 2. Design of plywood beams. Supplement 3. Design of flat plywood stressed-skin panels. Tacoma, Washington.

(2) AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. 1965 Designing buildings to resist snow and wind loads St. Joseph, Michigan. R 288 (T).

(3) AMERICAN WOOD-PRESERVERS' ASSOCIATION. 1970 American Wood Preservers' Association book of standards. Washington, D.C.

(4) AMERICAN WOOD PRESERVERS INSTITUTE. FHA pole house construction. Washington, D.C.

(5) AMERICAN WOOD PRESERVERS INSTITUTE. 1969 Pole building design. 6th ed. Washington, D.C.

(6) AMERICAN WOOD PRESERVERS INSTITUTE. 1969 Pressure-treated pole frame buildings survive hurricane Camille. Washington, D.C. Wood preserving, December 1969.

(7) AMERICAN WOOD PRESERVERS INSTITUTE. 1970 All-weather pressure-treated wood foundation. Washington, D.C.

(8) ANDERSON, L.O. 1968 Construction of Nu-Frame research house. Madison, Wisconsin, Forest Products Laboratory. U.s. Forest Service Research Paper FPL 88.

(9) ANDERSON, L.O. 1969 Low-cost wood homes for rural America: construction manual. Washington, D.C., U.S. Department of Agriculture. Agriculture Handbook No. 364.

(10) ANDERSON, LO. 1970 Wood-frame house construction. Washington, D.C., U.S. Department of Agriculture. Agriculture Handbook No. 73 (Revised).

(11) ANDERSON, LO. & SMITH, WALTON R. 1965 Houses can resist hurricanes. Madison, Wisconsin, Forest Products Laboratory. U.S. Forest Service Research Paper FPL 33.

(12) ANDERSON, L.O. & ZORNIG, HAROLD F. 1969 Designs for low cost wood homes. Washington, D.C., U.S. Forest Service.

(13) ARCHITECTURAL WOODWORK INSTITUTE. 1968 Quality standards of the architectural woodwork industry. Arlington, Virginia.

(14) BIM, J. & KOUKAL, M. 1969 Production of joinery for tropical countries. A paper prepared for presentation at a conference on Production Techniques in Wooden Houses Under Conditions Prevailing in Developing Countries, sponsored by the United Nations Industrial Development Organization, Vienna, Austria Doc. ID/WG 49/6.

(15) BLOMQUIST, R.F. 1969 Timber-framed construction for tropical climates. A paper prepared for presentation at a conference on Production Techniques in Wooden Houses Under Conditions Prevailing in Developing Countries, sponsored by the United Nations Industrial Development Organization, Vienna, Austria. Doc. ID/WG 49/2.

(16) U.S. FOREST SERVICE. FOREST PRODUCTS LABORATORY. 1961 Wood- floors for dwellings. Washington, D.C., U.S. Department of Agriculture. Agriculture Handbook No. 204.

(17) U.S. FOREST SERVICE. 1965 Timber trends in the United States. Washington, D.C. Forest Resource Report No. 17.

(18) GATCHELL, CHARLES J. 1967 Machine-driving of wooden posts Upper Darby, Pennsylvania, Northeastern Forest Experiment Station. U.S. Forest Service Research Paper NE 81.

(19) HURST, HOMER T. 1965 The wood frame house as a structural unit. Blacksburg, Virginia, Virginia Polytechnic Institute. Technical Bulletin No. 179.

(20) INTERNATIONAL WORKING GROUP ON TIMBER INFORMATION. 1969 Some facts concerning joinery work. Amsterdam Houtvoorlichtingsinstituut.

(21) LLOYD, WILLIAM B. 1966 Millwork: principles and practices. Chicago, Illinois, Cahners.

(22) NATIONAL FOREST PRODUCTS ASSOCIATION. 1964 Low-profile wood-floor system. Washington, D.C. Technical Report No. 4.

(23) NATIONAL FOREST PRODUCTS ASSOCIATION. 1967 Cost saving with the UNICOM method. Washington, D.C. Technical Report No. 6.

(24) NATIONAL FOREST PRODUCTS ASSOCIATION. 1968 National design specification for stress-grade lumber and its fastenings. Washington, D.C.

(25) PHELPS, ROBERT B. 1970 Wood products used in single-family houses inspected by the Federal Housing Administration, 1959, 1962, and 1968. Washington, D.C., U.S. Department of Agriculture, Forest Service, Statistical Bulletin No. 452.

(26) SOUTHERN FOREST PRODUCTS ASSOCIATION. How to build storm resistant structures. New Orleans, Louisiana.

(27) TIMBER DEVELOPMENT ASSOCIATION, LTD. 1957 Wood floors. High Wycombe, Bucks., England.

(28) TIMBER DEVELOPMENT ASSOCIATION, LTD. 1959 Wood flooring. High Wycombe, Bucks., England.

(29) TIMBER ENGINEERING COMPANY. 1956 Timber design and construction handbook. New York, F.W. Dodge Corporation.

(30) U.S. DEPARTMENT OF COMMERCE. 1970 American softwood lumber standard. Washington, D.C., National Bureau of Standards. Voluntary Product Standard
PS 20-70.


(31) COUNTRYMAN, DAVID. 1971 The use of glued and composite elements in housing. WCH/71/3/3.

(32) LEWIS, WAYNE C. 1971 Use of panel products in housing. WCH/71/3/2.

(33) PERCIVAL, D.H. 1971 Present and potential applications of treated pole and post construction for houses. WCH/71/3/4.

(34) PRANGE, GERALD F. 1971 Uses of sawn wood in housing. WCH/71/3/5.

Report of the consultation

1. This section reviews current practices in the use of wood in housing under five main headings: use of sawn lumber; use of poles and posts; glued and composite elements; panel products; flooring and millwork. More detail on the first four subjects was available to the participants in the form of background papers. The Consultation considered, as a base for its discussion, each of these documents. The detailed discussions resulted in the recommendations which follow.

2. The participants recognized that the intelligent harvesting and utilization of forest resources does not result in a depletion of a vital natural resource, as happens with mineral and petroleum resources, but represents only one stage in the continued renewal of this resource. They recognized also that economic utilization of the forest resource may be expected to result in a lesser impact on the environment than would utilization of other resources, in terms not only of pollution and production of troublesome residues, but also in terms of energy requirements for its conversion. Accordingly, the Consultation recommended to governments that they consider not only the economic but also the social benefits which would accrue from the use of wood products when they plan for the housing needs of their populations.

3. The participants recognized the absolute necessity for wood products to be of predictable size and quality if architects and builders are to use them effectively and efficiently in solving the world's pressing housing needs. They recognized as well, however, that the nature of the standards required to impart this predictability would be basically different for wood products intended for export and those intended for domestic use. The former must be closely related to the needs of the importing countries. Since these needs may vary from country to country, international standardization may be difficult or impossible. Domestic standards must be related not only to the needs of the country but also to the level of its technology, and the complexity and scope of these standards must rise as the country's technology advances. The participants did not attempt to enumerate all the standards which might be required for effective use of wood products in housing. Special attention was given, however, to the need for standardization of dimensions, of requirements for seasoning and preservative treatment, and the development of grading rules for lumber. In connexion with the latter, the training of graders and of supervising graders was cited as especially important. The importance of standardization of units of measurement in international trade was considered. Based on these considerations, the Consultation recommended to governments that, to ensure the most effective utilization of forest products in housing, they plan the development of appropriate standards consonant with the needs of each country and reflecting the degree of development of its technology.

4. The participants recognized the need to advance the level of technology in developing countries to ensure the most effective use of their resources. to reduce their dependence on imports, and to solve their housing problems most quickly and effectively. They recognized also that this might be done best by transferring technology from developed countries. At the same time, certain possible hazards were recognized. For example, the transfer of technology must be keyed to the current level of development and made in steps appropriate to this level. Second, the transfer must be truly one of technology and not of technologists; that is, local technicians and technologists must be trained in the technology. And, finally, care must be taken that the country receiving the technology does not become unduly dependent on the training country for equipment, materials and people. Accordingly, the Consultation recommend to international agencies and to governments operating bilateral aid programmes that they accelerate efforts to improve the level of technology of developing countries with due regard to the cautions expressed above.

5. The participants recognized the vital role which wood products can play in providing adequate housing. They recognized also the existence of biases against the use of wood in many areas and that poor performance could only increase these. They considered it vital, therefore, to emphasize the necessity for technically correct use of wood to avoid the faults which could result from the use of inadequately seasoned lumber, lack of preservative treatment, inadequate fastening and other technical shortcomings. Accordingly, the Consultation recommended to architects, builders and government agencies concerned with the provision of housing that they take all possible steps to ensure the technically correct use of wood products in housing.

6. The participants emphasized the need for adequate means of assembly of the components of a house and the necessity for using the most simple means consonant with needs. In general, it was agreed that nails provide the most suitable solution for most houses, with the additional necessity for supplementary attachments such as straps or bolts in areas of particularly high hazard, such as those subject to hurricanes, typhoons, or earth-guakes. More sophisticated methods of assembly, such as those involving adhesives or timber connectors. should be reserved for more complex structures and for countries at a suitable level of development. The need for research on methods of fastening very dense species was noted. The Consultation reminded architects and builders in developing countries of the desirability of employing methods of assembly of house components which are as simple as possible while providing the necessary strength and rigidity.

7. The participants recognized the need for development of adequate primary manufacturing facilities within developing countries to convert native timber resources to products if housing development is to proceed at an adequate pace. Accordingly, the Consultation recommended to governments of developing countries that, in their economic planning for housing development, they consider fully means by which financing for primary manufacturing facilities essential to the production of products required for housing may be ensured.

8. The participants noted and agreed with the concept expressed in Section 2 that developing countries should place special emphasis on the possibility of using, in housing, products derived from species of currently lesser importance and lower market value. While admitting their inability to give specific definition to such terms as " secondary species" or "little-used species" it was plain that some species have had limited commercial importance because of local bias, past emphasis on export markets and other factors unrelated to the actual value of the timber. They emphasized that many secondary species have excellent properties and that tile term should not be taken to imply low quality. Erection of demonstration houses was one technique which might be used to overcome existing bias against such species. The use of manufacturing residues as a source of products for housing was cited as being of potential importance. Accordingly, the Consultation recommended to governments of developing countries that they give serious consideration to the use, in the development of products for housing, of currency underutilized species and of manufacturing residues.

9. As technology develops, manufacture of more sophisticated products will be undertaken. For example, some developing countries are considering plants for the production of particle board which will require resins for binders. Procurement of such materials from overseas and even of such simple materials as nails requires foreign exchange. Accordingly, the Consultation recommended to the governments of developing countries that they consider, in their economic planning, the relative advantage of establishing within their borders, or on a regional basis, facilities for the manufacture of materials such as resins or products such as nails compared with purchasing them elsewhere.

10. The participants recognized that planning for the production or procurement of wood products for use in housing cannot be done effectively without the establishment of targets against which to measure need. Thus, the type, style and method of construction are all-important elements of planning. For example, what is the size needed? Is it to be totally of wood, of concrete with wood trim, doors, and windows? What cost level is anticipated? These are social, economic and political decisions which will be controlled by local conditions but are nevertheless factors which must enter into planning. Thus, the Consultation recommended to agencies concerned with the provision of housing that their early planning provide targets against which the need for wood products may be measured.

11. Materials for use in housing are expected to serve one or more of three functions: to provide structural support; to provide closure (or protection from the elements); to provide appropriate aesthetic quality. The degree to which a material is expected to perform these functions varies with local conditions. Thus, greater structural efficiency is required in areas subject to high winds or earthquake, closure requirements will be greater in areas of low temperature, and so on. Thus, the choice of materials for use in housing will depend both on the function they are expected to serve and the level at which they must perform that function. It was noted that suitable aesthetic treatment of houses may be expected to provide an appearance attractive enough to combat bias against the use of wood. Thus, the Consultation recommended that building research or similar organizations provide definitions of functions which materials are expected to perform as a base for their choice and as a base for providing the facilities for furnishing them.

12. The participants recognized that needs for research had been implicit in much of their discussion. Knowledge of the characteristics of underutilized species is vital to their efficient utilization. Improved methods of fastening the denser species are needed. Better means of disseminating research results are required. It was agreed that, in many cases, regional research centres would be advantageous, with some feeling that building research centres would be preferable to forest products research centres. The existence of mechanisms for dissemination of information on toe characteristics of tropical woods was noted. The need for research on building methods was also noted. It was assumed that such needs would be defined by Section 5. Accordingly, the Consultation recommended to international agencies that they seek opportunities for and assist in the establishment of regional technical centres for the dissemination of information and the development of wood products for use in housing. To IUFRO, it recommended that it accelerate its activities in gathering and disseminating information on tropical woods.

13. The participants noted that, in some cases, housing finance institutions were hesitant to provide financing except under the most favourable conditions because of a lack of means to evaluate the durability of a house and the problems and costs involved in its maintenance. Accordingly, the Consultation recommended that housing research organizations undertake development of means for predicting the effects on durability of various deteriorating influences, and of variations in building techniques.

14. The participants noted that the more effective utilization of wood in structures is severely hampered all over the world by the minor emphasis given to it in architectural and engineering curricula and the lack of suitable textbooks. Accordingly, the Consultation recommended that universities the world over be urged to modify their curricula to provide engineers and architects with adequate training in the use of wood in design and construction.

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