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A workshop provides a focal point at the farmstead for the repair and maintenance of machines, implements and structures. It also provides a place where tools can be stored in an orderly manner, a store for supplies and spare parts, and a shelter where work can be carried out during inclement weather. A facility of this type should be available on every farm. The size and design of a workshop, however, should be commensurate with the size of the farm and the work to be done in the shop.
The small holder may be adequately served with a tool storage cupboard that can be locked for security and a workbench with a simple homemade vice for holding tools while they are being sharpened or fitted with new handles. From this simple beginning a more complete facility may gradually evolve as the farm operation grows and more equipment is required. Since repair tools and supplies represent a considerable investment, most farmers will want to store them in a secure place. Many small scale farmers will not require a separate store for this purpose, but if stored together with hand tools and small implements, the number of items may motivate the farmer to build a storeroom by enclosing part of the workshop with solid walls. Figure 11.1 shows a simple work shelter and store suitable for repair work and the storage of small implements. Note that the doors to the store may be designed with racks and hooks to hold supplies and tools. Fuels and other combustible materials should not be stored with the tools. A simple work bench and vice can also be housed under the shelter.
At the other extreme, a large ranch or commercial farm may need a separate building with extensive equipment for maintaining the farm machinery, tractors and vehicles. A farmer may also use his workshop to do routine repairs and preventive maintenance during the off season, to build or modify some of the equipment used on the farm and to prefabricate building elements to be used in construction projects.
The workshop facilities should be cost effective. That is, enough savings should be realized from timely maintenance, repairs and construction projects to pay for the cost of the building and the necessary tools and equipment. Although it is difficult to put a monetary value on timeliness, there is no question that being able to make emergency repairs is important. Some farm operations (planting, spraying, milking) are more sensitive than others to prolonged interruptions, and having facilities to complete repairs on the farm can reduce delays to a minimum.
Other factors, apart from the farm size, which will influence the extent of the workshop facilities are the number and diversity of machines, the availability of service from dealers, and the interest and mechanical skill exhibited by the farmer and farm labourers. If necessary, a skilled mechanic may be employed. Without qualified personnel to use the shop it becomes questionable in value and may even contribute to more frequent breakdowns and additional expense due to careless work.
The workshop should be located close to the work centre of the farm and convenient to the farm home on ground that is well drained and sufficiently level to allow easy maneuvering of equipment. Where electric power is available, proximity to the power source should be considered.
In tropical climates the workshop may be a simple pole structure with a non-flammable roof. Unless dust is a problem, it may be feasible to leave the sides open to provide good light and ventilation. Heavy-gauge wire netting can be used to make the area more secure without reducing light or ventilation. A pole structure of this sort can be enclosed with offcuts or corrugated steel at a later time, but if this is done, there must be provision for several good-sized windows. While a simple earth floor is often satisfactory, concrete offers the advantages of an easily cleaned, level surface. To do a clean repair job, a clean work area is essential and this is particularly important when lubricated mechanisms are reassembled. The level surface is helpful in some assembly or alignment operations.
Figure 11.1 Small farm workshop with a secure storeroom.
The following additional features are important for a safe and efficient shop:
Equipment needed in the workshop will depend on the type and extent of work to be done. Generally this means those tools required to perform day-to-day maintenance on machines and to carry out general repair work and small construction jobs required on farm buildings and equipment. However, any shop, regardless of size, will need some simple woodworking tools, some means of sharpening field tools, and wrenches (spanners) of various types and sizes. If the shop equipment includes a welder, it should be located, in the interest of safety, away from the woodworking area and preferably near the main door where it can conveniently be used inside or outside the building.
Flammable materials such as sawdust, shavings and oily rags must never be allowed to accumulate in the workshop since they represent a fire hazard, and fuels should be stored in a separate area. Generally good order and cleanliness in the shop makes for efficient work, convenience and safety.
On many small-scale farms in Africa all cultivation and transport operations on the term are done manually. The few small-sized hand tools and implements used in such farming can normally be stored in any multipurpose store at the farmstead. The store needs only to be secure for protection of the equipment from theft and vandalism, and dry so as to avoid deterioration of the metal and wooden parts. The tools will last longer if they are cleaned and working surfaces are greased prior to storage. The tools may be hung on rails or hooks on the wall or from the ceiling for order and convenience and to protect them from dampness penetrating an earth floor in the store.
Implements such as ploughs, harrows and cultivators are damaged little by rust when left outdoors. If they are properly cleaned prior to storage and metal surfaces, particularly all threaded parts used for adjustments, are greased, then a little rust is not likely to harm performance enough to justify the cost of a storage structure. A fenced compound can offer adequate protection against theft during storage. Although implements containing wooden parts are more susceptible to decay, those parts can usually be replaced at low cost.
Tractors and other complex machines will function better when needed if they have been stored under cover and given a complete off-season check-up. An adequate storage structure for these machines is likely to be economically feasible.
For most purposes a narrow open-side shed with a welldrained, raised earth or gravel floor will be adequate for machinery storage. The sides of the building can be partly or wholly enclosed with netting or solid walls when security conditions make it necessary. The building must be high enough to accommodate the highest machine. A smooth, level floor makes it easier to attach and detach tractor-mounted equipment or to move other machines. The space required can be determined by obtaining the dimensions of all the machines and implements to be stored. Then, using graph paper, the outline of the machines can be sketched onto a plan view, allowing additional space for maneuvering. Any roof-supporting posts inside the building or in the open sides must be marked on the drawing, since they will restrict the way the floor space can be utilized. Since many machines can not be easily moved, it is desirable to arrange the stored machines so that shifting is unnecessary.
Figure 11.2 Narrow open-side implement shed.
Fire resistant construction is desirable where tractors, cars and other powered machines are stored. A pole structure with an earth floor, sheet metal walls, timber trusses and metal, asbestos-cement or sisal-cement roofing will offer adequate fire resistance.
Machinery stores and farm workshops are constructed in much the same way and are usually placed close together for convenience. In fact, they may be housed in one building with a workshop section at one end and machinery and implement storage in the balance of the building.
Many materials that are used on farms fall into the category of "hazardous materials", since they are either highly flammable or poisonous. The type and quantities of these materials requiring storage will vary from one farm or one cooperative store to the next and only a few basic requirements for safe storage will be considered here. Other materials frequently used on farms such as fertilizers and cement also have special storage requirements mainly because they are hydroscopic, i.e., they tend to pick up moisture from the atmosphere.
Storage of Hazardous Products
Hazardous materials should always be stored in a separate location containing only those materials. If the quantities are larger, flammable and poisonous materials should be stored in separate rooms. Ideally each type of material should have its own storage space, that is, its own shelf in a cupboard or a storage room, or its own room in a cooperative or merchant store.
Quantities of flammable products greater than about 3 litres of cellulose thinner, 10 litres of petrol, 20 litres of kerosene, 50 litres of diesel fuel should be stored in a separate building at least 15m from any other building. For this purpose a pole building with steel netting walls offers shade and security.
Any store for hazardous products must be well ventilated so that explosive or toxic fumes can not accumulate. Ventilation openings should be provided at both low and high levels or alternatively the door can be covered with netting. The store, including the ventilation openings, should be vermin proof to prevent rodents from breaking open packages. It must be possible to lock the store to prevent the theft of expensive materials and keep unauthorized persons, in particular children, from accidentally coming into contact with the hazardous materials.
Some chemicals are harmful to the skin. Therefore washing facilities should be available nearby for immediate use. Stores for hazardous materials should never have a drain in the floor as any spillage or washdown water containing the materials must be prevented from entering any watercourse or drinking water source. It is frequently recommended that the floor and lower part of the walls including the door sill be constructed of concrete to form a reservoir to contain any accidental spills. This type of store must be clearly marked with an appropriate warning notice.
Figure 11.3 Cabinet for the storage of chemicals.
Storage of Fertilizers and Other Non-hazardous Materials
Some fertilizers are hydroscopic and easily pick up moisture from humid air or from the ground. This causes them to become lumpy and to deteriorate. Cement, although not very hydroscopic, will deteriorate if exposed to damp conditions. Other materials may be adversely affected by prolonged exposure to high storage temperatures and therefore must be shaded. Fertilizers and cement are normally sold in plastic lined bags offering some degree of protection. They should be handled and stored so that the bags are not punctured or otherwise damaged. In addition the storage conditions should be as dry as possible. Bags should be placed on a raised platform in the store. This will allow ventilation and prevent ground moisture from penebating from below. The pile should be protected from rain by a roof or some other type of watertight cover. Fertilizer can be very corrosive to metals and should not be stored close to machinery or tools.
A greenhouse is a structure using natural light within which optimum conditions may be achieved for the propagation and growing of horticultural crops, for plant research, or for isolating plants from disease or insects. While in the tropical areas of Africa there are only limited applications, there are a few situations in which a greenhouse can be justified because of the optimum growing conditions required for a high value crop or a research project.
There is a wide range in the cost of various greenhouse designs and a careful assessment to relate the requirements for a given enterprise to the cost of the house is important. For example, a greenhouse used for year long flower production can justify the cost of glass, while a house used for a month or two for starting vegetable plants can only justify a polythene covering.
Site and Support Facilities
Greenhouses should be located in open areas with no shading from trees or buildings and with access to roads. The land should be nearly level and well drained with a fall of 1 in 100 to l in 200 being ideal. If possible, the site should be sheltered from excessive winds. However, normal air movement is essential for natural ventilation systems and to prevent locally stagnant conditions.
Good soil is essential, deep, medium-textured loam being ideal. Soils which are less than ideal should be worth improving. Very heavy soils are not usually satisfactory.
A good, clean water supply is of paramount importance. A full crop system may require up to 8,400m³ per hectare (840// m²) in a single year and the source of water must be able to supply all that will be required.
Electricity will be required if ventilation is to be mechanized and if stationary machinery is to be used in the greenhouse.
Design Parameters
Light
It is important that the crops being grown in a greenhouse receive the optimum amount of light, not only when the skies are clear (direct light), but also when it is cloudy (diffuse light).
The shape and construction of the house should be such that it will allow the best possible entry of light. The two shapes coming closest to the ideal are: a the single-span semicircular section covered with clear polythene film, Figure 11.4. b the mansard profile, a framed structure in which the sides and two roof sections are sloped in such a way that a semicircular cross section is approximated, Figure 11.5.
The size and cross section of all the load bearing members have a pronounced effect on light transmission.
The gutters of multi-span roofs produce considerable shade, and likewise, in wide-span houses, the heavier roof trusses tend to cause more shading. Thus open trusses with narrow-section members are desirable.
Light colors and reflective surfaces improve light transmission. In spite of a good design for natural light, artificial lighting may be needed for the production of photo-period sensitive plants.
Orientation
Within the latitudes found in the tropics it is desirable to orient the ridge of greenhouses north and south to reduce the overall shading by the framing members. This is true for all types of frames including multi-span houses.
Size
While multi-span blocks of 3.2m each are least expensive to build, wider spans will allow somewhat better light transmission. Furthermore, the general management in wider houses (movement of machines, optimum cropping layouts, etc.) may justify the extra cost. As a general rule the cost is lowest when the length is four to five times the span width. This is particularly true with wide-span houses.
Height
The height of a greenhouse should be sufficient for the operation of machinery and the comfort of the workers. An increase in height improves natural ventilation during still conditions and the desired plant climate is more easily obtained. However, with very high roofs, maintenance becomes more difficult. Gutter heights of 2.8 to 3.0m are recommended for multi-span houses to allow machines to move freely. In single-span houses, eave height should be at least 2m to allow for unrestricted work space.
Materials
Greenhouses are generally built of steel, aluminium or wood and are glazed with good quality glass, clear polythene sheet, or fibreglass-reinforced polyester panels.
Steel must be galvanized after fabrication as any welding or drilling breaks the galvanized layer. Steel is cheaper than aluminium and is ideal for the main roof frame.
Aluminium is very resistant to corrosion and is easily formed into complex sections. While it is expensive, it is most suitable for glazing bars. It cannot be economically welded and bolted construction is used.
Wood is less suitable for the lightweight construction and the high moisture conditions found in greenhouses, therefore only top grade timber of the most decayresistant species which has been treated with a waterbourne type of wood preservative should be used.
Figure 11.4 Semicircular greenhouse frame.
Figure 11.5 Mansard and gable greenhouse frames.
Glass is expensive, but it is the most durable covering and transmits the most light (90%). However, the gradual build-up of dirt and algae along with surface etching eventually causes a reduction in light transmission. The minimum width of glass ordinarily used is 610mm. Also common is the 730mm width. Both of these are 4mm thick and weigh 2.8 kg/m².
Polythene sheet is increasingly being used to cover relatively low cost structures. It has light transmitting qualities similar to glass but the material has to be replaced periodically as it deteriorates under the influence of ultraviolet light. However, the cost is much lower than glass and the roof framing can be much lighter, resulting in good economy.
Fibreglass reinforced polyester panels are more impact resistant than glass and more durable than polythene sheet. Light transmission is about 85% but drops off appreciably unless the surface is cleaned and resurfaced with acrylic sealer every 4 to 5 years. It is intermediate in cost between glass and polythene.
Ventilation
In tropical regions ventilation is likely to be the most important environmental control feature of the greenhouse. The exchange of air inside the building with air from the outside is used to lower temperature, reduce humidity, and to maintain a supply of carbon dioxide for photosynthesis. This is accomplished by natural means with vents and doors or by mechanical means with fans. A comprehensive discussion of ventilation is found in Chapter 7.
The ventilation rate is usually expressed as the cubic metres per second of airflow per square metre of floor area. To obtain a reasonable heat rise of less than 4°C in a glass-clad house, the airflow rate in the tropics should be 0.04 to 0.05m³/s and m² of floor area.
Polythene-clad houses do not become as hot due to the transparency of the plastic to longwave radiation which is transmitted back out of the house. Thus the ventilation rate for a polythene-clad house can be reduced to 0.03 to 0.04m³/ s and m². This further reduces the cost of a polythene-covered house.
Adequate natural ventilation is often provided by large doors at each end even though this may amount to only 3 to 7% of the floor area. These large doors not only aid in ventilation but also allow easy access to the greenhouse.
Cooling
Evaporative cooling can be used in greenhouses where ventilation alone is insufficient to maintain the required temperatures. Figure 11.6 shows the temperature reductions possible with evaporative cooling. Evaporative cooling is discussed in detail in Chapter 7.
Figure 11.6 Limits of evaporative cooling.
Shading
Shading is used to reduce light transmission and heat gain when necessary. In glass houses shading may be done simply by applying water-based whitewash to the inside of the roof to cut down light transmission. When the weather conditions are steady and reliable, whitewash is cheap and effective and easily washed off when the need is past. Whitewash as a shade seems particularly appropriate for shading in tropical areas.
Iowa State University, Planning and Equipping a Service Center for Your Farm, Ames, Iowa, Cooperative Extension Service Iowa State University, 1980.
Noton N.H., Farm Buildings, Reading, U.K., College of Estate Management, 1982.
Virhammar K., Plastic Greenhouses for Warm Climates, FAO Agricultural Services Bulletin 48, Rome, Food and Agriculture Organization of the United Nations, 1982.
Whitaker J.H., Agricultural Buildings and Structures, Reston, Va., Reston Publishing Co., 1979.
Food and Agriculture Organization, Agricultural Machinery Workshops: Design, Equipment and Management, FAO Agricultural Development Paper No.66, Rome, Food and Agriculture Organization of the United Nations, 1960.
