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Doors are essential in buildings to provide security and protection from the elements while allowing easy and convenient entry and exit. Farm buildings may be served adequately with unframed board doors, while homes will need more attractive, well-framed designs that close tightly enough to keep out dust and rain and allow only minimal air leakage. Large openings can be better served by rolling doors rather than the side-hinged type.
General Characteristics of Doors
Size: Doors must be of adequate size. For use by people only, a door 70cm wide and 200cm high is adequate. However, if a person will be carrying loads with both hands, e.g. 2 buckets, 100 to 150cm of width will be required. If head loads will be carried, door heights may need to be increased to 250cm. Shop or barn doors need to be considerably larger to give access for tools and machinery.
Strength and stability: Doors must be built of material heavy enough to withstand normal use and to be secure against intruders. They should be constructed of large panels such as plywood or designed with sturdy, well secured braces to keep the door square, thereby allowing it to swing freely and close tightly. A heavy, well-braced door mounted on heavy hinges fastened with 'blind' screws and fitted with a secure lock will make it inconvenient for someone to break in.
Door swing: Edge hung doors can be hung at the left or at the right and operate inwards or outwards. Careful consideration should be given to which edge of the door is hinged to provide the best control and the least inconvenience. An external door that swings out is easier to secure, wastes no space within the building, and egress is easier in case of emergency. However, unless it is protected by a roof overhang or a verandah, it may be damaged by rain and sun. An inward swinging door is better protected from the weather.
Weather resistance and durability: It is desirable to use materials that are not easily damaged by weathering and to further improve the life of the door by keeping it well painted.
Special considerations: under some circumstances fireproof doors may be desirable or even required. In cooler climates insulated doors and weatherstripping around the doors will help to conserve energy.
Types of Doors
Unframed doors: Very simple doors can be made from a number of vertical boards held secure with horizontal rails and a diagonal brace installed in such a position that it is in compression. These are inexpensive doors and entirely satisfactory for many stores and animal buildings. Because the edge of the door is rather thin, strap or tee hinges are usually installed over the face of the rails.
Figure 5.68 A simple unframed door.
Framed doors: A more rigid and attractive assembly includes a frame around the outer edge of the door held together at the corners with mortise and tendon joints. The framed door can be further improved by rabbeting the edge of the frame rails and setting the panels into the grooves 10 to 20mm. The door can be hung on strap or tee hinges, but since there is an outer frame the door can also be hung on butt hinges with hidden screws. If the inner panel is made up of several boards braces are needed, but if the one or two panels are made of plywood, no braces will be required. Large barn or garage doors will need the bracing regardless of the construction of the center panels.
Flush Doors: Flush panel doors consist of a skeleton frame clad with a sheet facing such as plywood. No bracing is necessary and the plain surface is easy to finish and keep clean. Flush panel doors are easily insulated during construction if that is necessary.
Double Doors: Large door openings are often better served by double doors. If hinged doors are used, the smaller double doors are not as likely to sag and bend and they are much less likely to be affected by wind. Usually opening one of the double doors will allow a person to pass through. Figure 5.70 shows how the meeting point of the two doors can be covered and sealed with a cover fillet.
When doors are large and heavy and need to be opened only occasionally, it is desirable to place a small door either within or next to the large door. Figure 5.71 shows typical locations for a small door for the passage of people.
Rolling Doors: An alternative to double-hinged doors for large openings is one or more rolling doors. They often operate more easily, are not as affected by windy conditions nor as subject to sagging and warping as the swinging doors. The rolling doors are usually mounted under the eave overhang and are protected from the weather when either open or closed. It is true that they require space at the side of the doorway when they are open, but there are several designs to suit a variety of situations. For example:
In all cases it is desirable to have guides at the base to prevent wind interference and to make the building more secure from intruders. For security reasons the door hangers should be of a design that cannot be unhooked but only roll on or off the end of the track. The most secure place to mount the door hangers is on the stiles (end frame pieces). See Figure 5.72 for details.
Half-Door or Dutch Door: Doors that are divided in half horizontally allow the top section to be opened separately to let in air and light while at the same time restricting the movement of animals and people.
Figure 5.69 Framed door.
Figure 5.70a Unframed door
Figure 5.70b Framed door
Figure 5.70c Flush door
Figure 5.71 Alternative locations of a small door for the passage of people.
Figure 5.72 Rolling door details.
A timber door frame consists of two side posts or jambs, a sill or threshold, and a head or soffit. For simple buildings not requiring tight-fitting doors, the two jambs as shown in Figure 5.73 may be all that are necessary. However, if a tightly fitting door is desired, then a complete frame is required including strips or stops around the sides and top against which the door closes. In as much as the door jambs are installed against the wall, and the fit may not be precise, dwelling house doors are often hung in an inner frame that can be plumbed and levelled by inserting shims between the inner and outer frames as shown in Figure 5.74.
Figure 5.73 Simple timber door frame installation.
Figure 5.74 Framed timber door in concrete block wall with jamb blocks.
This figure also shows the use of concrete jamb blocks which are often available for concrete masonry walls. They have a corner cut out so that when the wall is laid up there is a recessed area in which to install the jamb rigidly. A door frame may be anchored in an opening where square end blocks are used as shown in Figure 5.75.
The simplest doors do not close tightly because they have no threshold or head. A threshold allows the door to close with a relatively tight fit at the bottom while at the same time allowing the door to swing open with adequate clearance from the floor. The head permits the top of the door to close tightly.
Simple Locks for Barn Doors
Large double doors are normally secured by locking them both at the top and the bottom. Thus four sliding bolt locks are required and should be installed close to where the doors meet. In small double doors top and bottom locks are only required for one of the doors. Figure 5.77a illustrates a simple wooden handle locking with a wedge nailing to the lintel. It can be used at the top of an unframed door. Note that the top rail must be placed down far enough to allow movement of the top of the handle. In, for example barn doors, where movements of the door can be tolerated, often only a lock at the top is provided.
Alternatively the lock shown in Figure 5.77b can be used This lock, which is located at the middle rail, has a bolt running through the door. The bolt is secured to a cross bar on the inside and a handle on the outside. When the handle is pressed down the cross-bar rotates out of the hooks. A padlock can be fitted to secure the handle in locked position.
Windows provide light and ventilation in a building an allow those within to view the surrounding landscape and observe the activities in the farm yard. In sitting rooms and work rooms where good light and ventilation are important, the window area should be 5 to 10% of the floor area of the room. Windows sometimes need to be shaded to reduce heat radiation or closed to keep out driven rain or dust. In addition screening may be needed for protection from insects. Shutters, either top-or sidehinged, are commonly used to provide the needed protection. Side-hung glazed windows, fly screens and glass or timber louvres are also used.
Figure 5.75 Anchoring a doorframe in a masonry wall without jamb blocks.
Figure 5.76 Types of thresholds.
Figure 5.77 Simple barn door lock.
Shutters: These are basically small doors and are constructed as unframed, framed or flush shutters. Because of the smaller size only two rails are required and the timber can be of smaller dimension. The principles of construction are the same as for doors. However, when the frame for the shutter is recessed in the wall, the sill must be sloped and extend out from the wall to let the water drip clear of the face of the building. The window shutter can be sidehinged or top-hinged. A top-hinged shutter has the advantage of shading the opening when kept open as weld as allowing ventilation while preventing rain from entering.
Glazed windows: Glazed windows are relatively expensive but are most practical in cold areas. When temperatures are low, the window can be shut while daylight still enters the room. Frames for glazed windows are available in wood and metal, the latter being more expensive. Glazed windows with frames are usually marketed as a unit, but Figure 5.81 illustrates various methods of frame construction and installation.
Figure 5.78 Recessed window or shutter.
Figure 5.79 Window installations.
The angle, as determined by height and the horizontal distance available, will determine the most suitable means of getting from one level to another. For a slope up to 1:8 (7°). A ramp is suitable for both walking and pushing a wheelbarrow. For walking alone, a 1:4 ( 14° ) slope is satisfactory if it remains permanently dry. For slopes between 1:3 and 1:0.8 (18 to 50°), stairways are possible, although 30 to 35° is preferred. Angles steeper than 50° require a ladder or ladder-stairway. Temporary ladders should be set up at 60 to 75°, while a fixed ladder may be vertical if necessary.
Ramps: Ramps may be made of tramped earth or concrete. An earth ramp should be made of a mixture of fine gravel and clay, the gravel to give texture for a nonslip surface and the clay to serve as a binder. The surface of a ramp constructed of concrete should tee 'broomed' across its slope after having been poured and struck off.
Stairs: Stairs can be designed as one straight flight, with a landing and a 90° turn or with a landing and a 180° turn. The straight flight is the simplest, the least expensive and the easiest on which to move large objects up or down. However, stairs with a landing are considered safer because a person cannot fall as far.
Definitions and descriptions of terms relating to stairways: (see Figure 5.80).
Angle block: Glued angle block in the junction between tread and riser to reduce movements and creaking.
Balusters: The vertical members between the stringer and the handrail.
Going: The horizontal distance between the nosings or risers of two consecutive steps. This is sometimes called the run or the tread.
Handrail: A safety rail, parallel to the stringers and spanning between newels at either end. This can be attached to the wall above and parallel to a wall stringer. The vertical distance between the stringer and handrail should be 850 to 900mm.
Headroom: The vertical distance between the treads and any obstruction over the stairway, usually the lower edge of a floor. The headroom should be at least 2 metres.
Housing: The treads and risers can be housed in grooves in the stringers or supported on beads that are nailed and glued to the stringers. In both cases they should be secured with wedges and glue.
Newel post: The post supporting the hand-rail at the bottom, turn and top of a staircase.
Pitch: Usually 30-35°
Rise: The vertical distance between two consecutive treads.
Risers: The vertical members between consecutive treads. Sometime the riser is omitted (open riser) for simplicity and economy. In that case the treads should overlap by 25 to 35mm.
Steps: The combined treads and risers.
Stringers: The inclined beams supporting the steps. The strength required for the stringers will depend on the load and method of support. They may be supported only at the ends or continuously along the wall.
Treads: The members stepped on as a person climbs the stairs. The treads must be strong enough to carry and transfer the imposed load to the stringers without excessive deflection. They should have a non-slippery surface. The treads can be housed in grooves in the stringers or supported on beads that are nailed and glued to the stringers. In both cases they are secured with wedges nailed and glued to the stringer.
Width: Sufficient width for two persons to pass requires a width of 1.1 metre. A minimum width of 600mm can be used for traffic of persons not carrying anything.
Figure 5.80 Stairway construction.
The pitch for most stairs should not exceed 42° nor be less than 30°, and for stairs in regular use a maximum of 35° is recommended. For most stairs a minimum going of 250mm and a maximum of 300mm should be adopted, although in domestic stairs a minimum of 200mm is acceptable for stairs that are used infrequently. A rise from 150 to 220mm is usually satisfactory. Comfort in the use of stairs depends largely upon the relative dimensions of the rise and going of the steps. Rules for determining the proportion are based on the assumptions that about twice as much effort is required to ascend as to walk horizontally and that the pace of an average person measures about 585mm. Thus, the fact that a 300mm going with a rise of 140mm or 150mm is generally accepted as comfortable, results in the rule that the going plus twice the rise should equal 580 to 600mm.
It is essential to keep the dimensions of the treads and risers constant throughout any flight of steps to reduce the risk of accidents caused by changing the rhythm of movement up or down the stairway.
Stairs are constructed by gluing and wedging the treads and risers into the housing grooves in the stringers to form a rigid unit as shown in Figure 5.80.
Stairs are designed to be either fixed to a wall with one outer stringer, fixed between walls, or freestanding, the majority of stairways having one wall and one outer stringer. The wall stringer is fixed directly to the wall along its entire length or is fixed to timber battens plugged to the wall. The outer stringer is supported at both ends by the posts. The posts also serve as the termination point for handrails which span between them.
The space between the handrail and the tread may be filled with balusters, balustrade or a solid pannel to improve both the safety and appearance of the stairway.
Reinforced concrete is better suited for outdoor stairs than is timber. The number, diametre and spacing of the main and distribution reinforcement must always be calculated for each stairway by an experienced designer.
Figure 5.81 Typical formwork for casting concrete stairs.
Ladder-stairway The recommended pitch for this type of steep, narrow stairway is 60°. The width is usually about the minimum of 600mm. The size of the going (tread) is. dependent on the pitch. The values in table 5.17 are recommended:
Table 5.17 Measurements of Tread and Rise at different pitch of the stairway
Timber ladders are basically of two types:
Figure 5.82 Ladder-stairway.
Figure 5.83 Two basic types of ladders.
Figure 5.84 Ladder guard.
The width of the ladder should be 350 to 500mm and the rise should be 230 to 400mm, with 300mm as the recommended value.
Ladders which are moved from place to place should have hooks and dowels so that they can be thoroughly stabilized at the bottom and top. Ladders mounted permanently should be firmly secured in their position, and if necessary, provided with handrails. If the total length is more than 5 metres and the pitch steeper than 70°, the ladder should be provided with a guard preventing the climber from falling backward. If the ladder is taller than 2.5 metres and starts from a small platform, it too should have a guard.
Electrical energy can be put to many uses and an increasing number of farms will benefit from electrification as the electrical supply network is expanded in the rural areas or generators are installed at farms. Although few farms, in particular small farms, are connected to an electrical supply at present, everyone concerned with design and construction of farm buildings will need to have an appreciation of the general layout and function of electrical installations.
Figure 5.85 Typical electrical distribution system.
For most types of farm buildings the electrical layout can be drawn on a copy of the plan view by use of the symbols shown in Figure 1.8. The layout should indicate where outlets, lighting points, switches, motors, heaters and other appliances are to be fitted and the accompanying specifications should describe the chooser wiring system, fixing heights and detail each appliance. Detailed wiring plans and installation designs prepared by a specialist will only be necessary for large and complex buildings, such as plants for processing of agricultural produce.
Electricity supply to a farm will normally reach it overhead from a local transformer substation where the voltage has been redued to a three-phase, 415/ 240V supply. Four wires are required for a three-phase supply, one for each of the lines and one common return or neutral. The neutral is connected to earth at the substation. The voltage between any phase wire and the neutral is 240V, while it is 415V between any two phase wires. If nearly equal loads are connected to each of the phases, the current in the neutral will be kept to a minimum. To achieve this most appliances that consume large amounts of electricity, notably electrical motors and larger heater and air-conditioning units are designed for connection to a three-phase supply. Lighting circuits, socket outlet circuits and appliances of low power rating are served with single-phase supply, but the various circuits are connected to different phases to balance the overall loading. However, sometimes small farms or domestic houses are served with a single-phase, 240V supply. In this case only two wires are required in the supply cable, one live and one neutral. The balancing of loading is effected at the substation, where the lines from several houses are brought together.
The intake point for the main supply to a farm should be at a convenient place that allow for the possible distribution circuits. The intake point must provide for an easily accessable area that is protected from moisture and dust and where the main fuse, the main switch and the meter can be fitted. Circuit fuses and distribution gear may be fitted at this place or in each buildings at the farmstead that is to be served with electricity.
Electricity tariffs are the charges that are passed on to the consumer. The charges commonly consist of two elements, a fixed cost that often depend on the size of the main fuse, and a running cost that depend on the amount of electric energy consumed. The required amp rating for the main fuse will depend on the maximum sum of power required for appliances that are to be connected at any one time and is also influenced by the type of starter used for electrical motors. Usually the motor having the highest power rating will be the determining factor at a farmstead.
Earthing and Bonding
Should a base live wire touch or otherwise become connected to the metalframe work of an appliance, a person touching this would receive an electric shock. A precaution against this is to connect any exposed metal work to an earth wire, that is lead as an extra conductor in the supply cable and connected to an earthing connector, which consist of a number of copper rods driven well into the ground. An earthing wire will thus be carried as a third conductor in single phase supply cable and as a fourth or fifth conductor in a 3-phase supply cable, depending on whether the cable include a neutral wire. The neutral should not be used for earthing. Some appliances are, instead of being earthed, protected by being enclosed in an insulating cover.
Bonding is a low resistance connection between any two point of an earthed system as to prevent any difference of potential that could produce a current and is an additional protection. If, for example, the metal furnishing in a milking parlour is electrically connected to the reinforcement bars of the concrete floor, the cows will be protected from electrical shocks, should for some reason the furnishing become charged by an earth-leaking current, that is not large enough to blow a fuse, since the floor will get the same electrical potential.
Electricity is distributed within buildings in cables, which consist of one or several conductors made of copper or aluminium each separately surrounded by an insulative material, such as plastic, and then enclosed in an outer sheet of plastic or rubber. The size of a cable is given by the cross-section area of its conductors. All cables are assigned a rating in amperes, which is the maximum load the cable can carry without becoming overheated. Large conductors are usually divided into strands to make the cable more flexible.
Surface wiring is normally used in farm buildings. This implies sheeted cables laid on the surface of walls, ceilings, etc. and fixed with clips. Care must be taken that cables are not sharply bent, are protected when passing through a wall and are laid well away from water pipes. Conduit wiring, where the cables are drawn in concealed tubing, is to expensive and complex to be employed in farm buildings.
Lighting circuits are normally carried out in 5A fusing and wiring ( 1.0mm² cables). While a suitable arrangement of one-way and two-way switches will allow lamps to be switched on and off individually or in groups, each such circuit can serve for example ten 100W lamps without danger of overloading. If all ten lamps are on together they have a power requirement of 1000W. Following the relation:
W=V x A where:
W = power
V = voltage
A = current
The lamps would produce a 4.2A current in a 240V circuit, i.e. it leaves a suitable factor of safety to overloading the fuse and wiring.
Socket circuits are normally carried out in 2.5mm² wiring and arranged as ring circuits that are supplied from the mains at both ends through 10 to l5A fuses. In domestic installations a socket circuit can carry any number of outlets provided it does not serve a floor area greater than 100m². However, when designing socket circuits for farm buildings, such as the workshop, it will be wise to estimate the current produced by all appliances that are expected to be connected at any one time to avoid overloading. Lamp fittings, switches and outlets are available in a range, offering varying degree of protection against dust and moisture penetration. Although more expensive those offering a high level of protection will normally be required in farm buildings as will fittings positioned outdoors.
No socket outlets are permitted in bathrooms and showers and should be avoided in rooms such as clairies and wash rooms, because of the presence of water.
Fixed electrical apparatus that are single phase supplied, such as water heaters, airconditioners and cookers, should have their own circuits with individual fuses.
Three phase electrical motors and apparatus required power supply cables with four or five conductors, including the earthing wire. Each appliance should have its own power supply and the phase lines must be fused individually. Movable 3-phase motors are supplied from special 3-phase power outlets via a rubber sheeted flexible cord that is fixed to the motor at one end and fitted with a 3-phase plug at the other. All flex cords must be protected from damage by for example wheels and should where possible be hung off the ground. Flex cords must under no circumstances be connected by twisting the conductors together.
In tropical countries with strong natural light even relatively small windows may provide' sufficient indoor lighting. Hence artificial lighting will mainly be required to extend the hours of light.
The two most commonly used artificial light sources, where electrical energy is available, are in candescent bulbs and flourescent tube. Tubes and fittings for tubes are more expensive than bulbs and bulb fittings, but tubes produce three to five times as much light per unit of electric energy, have up to ten times as long life and have a lower heat production. Hence flourescent light normally is the cheapest despite the higher initial cost. However, in small rooms where the light is switched on and off frequently bulb fittings are usually preferred as the installation cost in this case is more important than the energy cost. Merary vapour and sodium lamps are often used for outdoor lighting. They have higher efficiency in terms of light produced than flourescent tubes, but their light covers only a limited spectrum and this tend to distort colours.
Various types of fittings are normally available for both bulbs and tubes. While a naked bulb or tube may be sufficient in some circumstances, fittings that protect the lamp from physical damage and moisture penetration will often be required in farm buildings. From an optical point of view the fitting should obscure the lamp and present a larger surface area of lower brightness to reduce the glare caused by excessive luminance contrast. This is particularly important if the lamp is positioned where it will be directly viewed. A lighting point must also be positioned so that reflected glare and trouble some shading of a work area is avoided. While light colours on interior surfaces will create a bright room, shades of blue or green produce a feeling of coolness. The dusty conditions in many farm buildings implies the use of fittings that allow for easy cleaning. Accumulated dust can reduce the flow of light by more than 50%.
Most agricultural production operations carried out in buildings can be performed quite satisfactory using natural light, but where artificial light is to be installed the standard of illumination should be related to the activities carried out. While the installation of 2.0 to 3.0W flourescent light per square metre floor area will be sufficient for general illumination, work areas need more light, say 5 to 8 W/ m², and a desk or work bench where concentrated or exacting tasks are performed may need 10 to 15 W/m² or more. Where bulbs are to be installed instead of tubes the above values will have to be at least trippled.
Figure 5.88 Examples of light fittings for farm buildings.
Single phase motors in sizes up to about 1kW have a wide range of applications, particularly for use in domestic appliances. The most common type, the single phase series motor or universal motor, produce a good starting torque and can be run on both alternating current (AC) and direct current (DC). While it has the advantage of being able to be connected to an ordinary socket outlet, generally, it can not compete with the performance and efficiency of a 3phase motor.
The 3-phase induction motor is the most common electrical motor at farms, where it is used to power fans, transport devises, mills, etc. Modern electrical motors are manufactured in a wide range of power ratings and types. Their enclosures range from screen protection to totally enclosed. Motors used in farm buildings normally should have an enclosure that is dust-tight and sprinkle-proof, i.e. it should not be damaged by being exposed to sprinkling of water from any direction. However, sometimes even better protection, such as dust-proof and flush-proof, is required and submersible motors must be totally enclosed and completely water proof.
Inherent features of the induction motor are its poor starting torque and heavy starting current - up to six times the full load current. To prevent excessive voltage chop in the supply network and Electricity Company usually allow only small induction motors to be started direct on line. A star/ delta starter is commonly fitted to motor above 2 to 3kW, and will reduce the starting current to about twice the full load current. Unfortunately it also reduces the already poor starting torque even further so that the motor can not start against heavy load. Other types of motors and starters are available for situations where starting against load can not be avoided, however.
The starter for any motor rated above about 0.5kW must incorporate an overloadction that switches off should the current exceed a safe value for longer time than what is required to start the motor. In many installations it would, in addition, be desirable to include a release mechanism that prevent unexpected restarting after a power failure. A wide range of sensors, timers and other devises are available for automatic supervision and control of electric motor operation.
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