Chapter 6 Building production

Contents - Previous - Next

Building production is the organization and management of the plans, equipment, materials and labour involved in the construction of a building, while at the same time complying with all codes, rules and contractual stipulations. The procedure should be designed to run efficiently, to keep the costs low and to allow returns on the investment to be realized as early as possible.

While many topics included in this chapter, such as standardization, organization of building works carried out by a contractor, tendering, contracting, inspection and control and progress charts may have limited relevance for small scale building projects on African farms, it is felt that an agricultural engineer will need some knowledge of these topics when faced with construction of communal and central facilities for agriculture and medium-to largescale farm buildings.

The costs of farm buildings such as animal housing and stores for produce can be expected to be repaid in terms of increased production, improved animal health, reduced storage losses, increased quality of produce and more efficient work performance. Other buildings such as dwellings are expected to be worth their costs mainly in terms of the standard of space, environment, convenience, construction and appearance they provide. The term "costs" in this context means costs over the whole life of the building, including operating and maintenance costs as well as an annual portion of the initial cost of construction, which in addition to building materials and construction labour, includes fees paid to consultants, architects and legal advisors as well as capital interest and any loss of production incurred during the construction phase.

Building planning is thus concerned with economic building rather than with cheap building, i.e., with providing the required standard of facilities at the lowest cost.

It should be pointed out that costs include not only cash payments but also the value of materials and work provided by the farmer and his family since these are resources that could have been used for alternative activities at the farm to generate income or produce food. Most methods for construction- costing and economic feasibility studies imply that resources employed for the construction as well as the benefits of the finished structure can be valued in a convenient monetary unit. Subsistence farmers are part of the monetary economy to only a limited extent, thus it is difficult to put a fair price on material and work supplied by these farmers for construction at their farms or to correctly value the benefits of the structure.

There is a national interest in utilizing efficiently the resources invested in buildings. Governments express their minimum demands in the form of building regulations, codes and laws.

A farmer employing an agricultural engineer to design a building, a contractor to construct it and suppliers to deliver material will expect delivery of work and goods to the standard and price agreed upon. For later reference it is common to specify the agreement in a contract, which makes reference to drawings and specifications for the structure and to general specifications. Inspections and controls are the means used to ensure that the agreement is followed.

The building production process

The building production commences when the farmer starts to seriously consider investing in a structure and does not end until the finished building is in use.

The process is divided into stages which follow in logical sequence. Each stage is terminated by a decision. Table 6.1 is an outline plan of work for the building production process. In small projects where the farmer performs virtually all tasks involved, it may not be necessary to follow the chart in detail. Nevertheless the same procedural basics and logical order should be a goal. During the initial planning stages, the costs are low compared with the importance. The high costs involved in correcting errors once the site operations and construction are under way, can be avoided if time is spent working out a good, functional design which is technically and economically sound.

Methods of construction

The methods of constructing farm buildings refers to the way in which units and components of the building structure are produced and assembled. The manner of organizing this process differs from region to region and depends on the level of technology and the materials available. The operations involved in the construction of rural buildings of traditional designs are familiar to most rural people in Africa and small buildings on farms are usually constructed by the farmers and their families. However, where new methods of construction, materials or layouts have been adopted, as well as where there is an increase in the size of the project, the assistance of trained artisans will usually be required. Self-help projects for the construction of communal facilities such as village stores must be accompanied by a training programme for the people involved.

Where most of the construction is done by employed building workers, three different contemporary building methods, which are described below, can be distinguished. While in the foreseeable future the traditional method of constructing farm buildings will remain the most common, the fact that an increasing number of industrialized building products are being marketed has lead to the introduction of post-traditional building and, to a limited extent. system building.

Table 6.1 Building Production Process Part 1

Table 6.1 Building Production Process Part 2

Traditional Building

In traditional building, forms of construction are those evolved by the traditional building crafts, particularly those of walling, roofing, plastering, carpentry and joinery. This method is a process of combining many small units. Most of the fabrication and assembly takes place at the site and usually in the position that the unit is to occupy in the completed structure. Within each tribal culture, traditional building results in structures that are similar but differing slightly, depending on the specific requirements and site.

Because of the limited range of materials and forms of construction used, the craftsmen are familiar with the content and order of operations in their own trade and their relation to operations in other trades so well that they carry it out with a minimum of detailed information.

The traditional craft-based building method is flexible and able to meet variations in the demand of the market on the work of the craftsmen more readily and inexpensively than methods based on highly mechanized factory production. This is because production is by craftsmen and there is little investment in equipment, especially mechanical equipment, and factory buildings.

However, the proportion of skilled labour required at the site is fairly high.

Post-traditional Building

The post-traditional or conventional method of building mixes traditional and new forms of construction, involving both the old crafts and newly developed techniques based on new materials. To some extent traditional building has always been in a state of change, but the introduction of Portland cement and mild steel has made it feasible to construct large and complex buildings and with this arises the need for efficient organization of the construction process.

The amount of on-site fabrication has been reduced by the introduction of prefabricated, factory-produced components, especially in the field of joinery and carpentry (windows, doors, cupboards, roof trusses, etc.). Reinforced concrete and preformed steel lend themselves to off-site fabrication of parts and only their assembly on site.

Post-traditional building varies from the traditional mainly in the scale of the work carried out and in the use of expensive machinery for many operations. The use of prefabricated, standardized components reduces the amount of skilled labour, but at the same time reduces the freedom of the designer in meeting varying design requirements. The scale of operation makes it necessary to pay greater attention to planning and organization of the work so that material and labour are available in a continuous flow, the mechanical equipment is efficiently used, and the construction can proceed smoothly. It is thus necessary to consider the production operations during the designing stage.

System Building

System building is a method in which most of the building's component parts are factory-produced and siteassembled. The main advantages in system building are the possibilities for efficient factory production of large numbers of similar building elements and the reduced period of time necessary for assembly at the site. A disadvantage with this method is the high level of accuracy required for setting out and foundation work since the nature of the components and the principles of the system are such that mistakes are difficult to correct during the assembly process. The components (e.g., wall, floor, ceiling and roof elements) are usually related to a specific building type, such as houses, schools or warehouses or to a restricted range of types. The design of buildings produced by this method is inflexible and limits the possibility of adjusting to specific requirements at a certain site or to a local building tradition. The building components may, for example, be produced for only a specific width of building and if the wall elements are say 3.6m long, the building length must be a multiple of 3.6m

Components of one system will not ordinarily fit with components of other systems, a situation referred to as a 'closed system'. On the other hand, en 'open system' allows each component to be interchanged and assembled with components produced by other manufacturers. In order to keep the variety within acceptable limits for mass production, such a system must operate within a framework of standardization of the main controlling dimensions, e.g floor-to-ceiling height of wall elements'


Prefabrication is the manufacture of building components either on-site (but not in-situ) or off-site in a factory. The use of prefabricated components can reduce the need for skilled labour at the site, simplify construction by reducing the number of separate operations, and facilitate continuity in the remaining operations. However, prefabs are not necessarily timesaving or economical in the overall construction project. For example, the use of prefabricated lintels may save formwork and result in continuity in the bricklaying work, but would be uneconomical if a lifting crane is required at the site to place them, when it is not required for any other purpose on the job.

On-site Prefabrication

On-site prefabrication may be of advantage where a number of identical components such as roof-trusses, doors, windows, gates and partitions are required. Once a jig, mould or prototype has been made by a skilled craftsman, a number of identical components can be produced by less-skilled labour, e.g. the farmer who could do this job in available time during the off-season. Prefabrication of such items as roof-trusses will also make for more convenient and effective production than construction in-situ.

It is advantageous to prefabricate some concrete components. Components for elevated positions require simpler formwork if cast on the ground or in the ground so that the soil can be used to support the formwork. Prefabrication eliminates the waiting time for concrete components to harden sufficiently for subsequent on- site operations to continue, but the weight and size of concrete parts may make prefabrication impractical.

Local production by farmers of adobe bricks, burnt bricks, soil blocks, etc. is not normally referred to as prefabrication although similar planning and organization are required for the production of these units as for production of prefabricated building components.

Off-site Prefabrication

Factory production of components requires capital investment in machinery and premises, a high degree of organization of work, standardization and a steady demand for the products. Building components, which can be economically produced in a factory, essentially fall into three categories:

Factory production is relatively inflexible, since large runs of any one component are essential for economical operation. The mere transfer of a simple operation from a site to a factory will not in itself reduce costs; on the contrary, it may increase them. This is particularly true for components for farm buildings, since the demand for them originates from a large number of scattered construction projects resulting in high transportation and distribution costs. Therefore many factory - made components used in farm buildings will have been designed primarily for other purposes.

Dimensional coordination and standardization

In order to limit the variety in size of similar components, to facilitate their assembly at the site, and to make them interchangeable between different manufacturers, building components are manufactured in standardized dimensions based on an accepted system of dimensional coordination. Such preferred dimensions are given in standards together with specifications for minimum requirements of technical performance. When the experience gained in factory production of components increases, the technique will be applied to components of increasing size and complexity (e.g., wholly finished wall elements) and this will increase the need for dimensional coordination.

One system of dimensional coordination uses the international basic building module of 100mm. The reference system establishes a three-dimensional grid of basic modules, or very often multi-modules of 300mm, into which the components ft.

The modular grid does not give the size of the component but does allow space for it. In order for the component to fit correctly, it will always be slightly smaller than the space allowed for it. The system must allow for some inaccuracy in the manufacturing process and changes in size due to changing temperature and moisture conditions.

This is expressed as a tolerance in size. For example, a window which is allowed a basic size of 1200mm for its width is produced with a working size of 1190mm and a manufacturing tolerance of 5mm, which is expressed as 1190 + 5mm. The actual dimension of a window delivered to the site would be somewhere between 1185mm and 1195mm. The joint would be designed to take these deviations into account.

Modular-size concrete blocks are 290mm long and modular format bricks are 190 x 90 x 40 or 90mm actual size to allow for 10mm mortar joints and plaster. The actual size of openings will then be 1220mm. In this process the designer has a responsibility to specify tolerances that can be achieved with available craftsmen and factories. It will be easier to fit factory produced window and door casements, which are made to standard modular sizes, if these sizes are also used when bricks and blocks are manufactured locally. The common brick size of 215 x 102.5 x 65mm allows for laying four coarses to 300mm vertically and four brick lengths to 900mm horizontally, if 10mm joints are used.

Figure 6.1a Grid of 3M multi-modules between zones of 200mm alowed for load-bearing columns (A). Building components such as partition components (B), external- wall components (C) windows (D) and door sets (E) are manufactured in sizes. which are multiples of the 3M multi-module.

Figure 6.1 Dimensional coordination.

Building legislation

In urban areas, government authorities issue building regulations to provide for the safety, security and welfare of those who use the buildings and to make maximum use of the scarce resources available for building construction. Typically the building regulations will cover such subjects as building materials, structural integrity, fire precautions, thermal and sound insulation, ventilation, window openings, stairways, drainage and sewage disposal. Building regulations may state minimum functional requirements, such as room height and space, for specific types of rooms. Additional legislation applicable to buildings may be found in the public health act and public road act. The building regulations and other legislation are statutory, i.e., they must be followed as far as they apply. The local authority will ensure that the legislation is complied with through its building-inspector, health inspector, etc. However, the authorities will sometimes, in addition to the regulations, issue guidelines for building. These are mere recommendations and the designer may diverge from them if there are good reasons.

Building regulations do not normally apply to farm buildings outside of urban areas, but there may be instances where other legislation is applicable, for example, where a farmer wants to connect to a main water supply or a main sewer or carry a drain under a public road. There fore it is wise to contact the local authorities about any new building proposal or major alteration to an existing building. If a local authority's approval is necessary, copies of drawings and specifications will have to be submitted for its advice and approval.

Contents - Previous - Next