Bamboo is an excellent building material for several reasons:
· it has a very high strength-to-weight ratio -- very sturdy for such a light-weight material;
· it is easily handled, with little waste and no bark to remove;
· it adapts to a variety of uses; a few bamboo plants in the backyard will provide enough bamboo for a fence, a pigpen, extra rooms, or a house;
· after construction, bamboo can be used for other income-generating crafts such as baskets, mats, and so on.
About the only parts of a building that cannot be made from bamboo are fireplaces and chimneys. However, bamboo is rarely used as the only construction material for a whole building. Usually it is combined with other materials: wood, clay, lime, cement, iron, palm leaves, thatch, and so on.
There are many bamboo species. They differ in thickness, strength, flexibility, and resistance to insects and decay. Each is useful in only a few parts of a building. For example, a species that makes good supporting columns cannot be used to make screen matting for a window. The general characteristics of different species are discussed below. But when in doubt about a specific bamboo supply, the best thing to do is check local practice and/or seek advice from a local contractor.
To balance its advantages, bamboo has many drawbacks as a construction material:
· Uneven Dimensions. It is usually necessary to have a large supply in order to weed out pieces that are too thin, too crooked, broken, or otherwise useless.
· Uneven surfaces. Variations in the diameter of the shaft (called a culm), in the prominence of the nodes, and in the rate of tapering at the end of the culm all make certain applications difficult. On the other hand, long culms can often be cut up and the tips used for one purpose while the shafts are used for another.
· Brittleness. In almost all cases bamboo cannot be nailed. Most bonds are made with wire or hemp lashings. A few thick-walled species can be bored to insert pegs.
· Low durability. Bamboo is susceptible to insects (especially beetles and termites) and to rot. Both insect decay and rot can be chemically retarded, and some species are more resistant than others. But even in the best cases, bamboo cannot last much more than 5 years in weight-bearing parts of a building.
Bamboo is basically an above-ground material. Unless it is treated with a preservative, it will last only 2-3 years underground.
However, bamboo will serve as a supporting post: for a house on stilts, for example. Use the largest diameter culms (at least 1220cm) with closely spaced nodes for stiffness. If only smaller shafts are available, they can be bound into columns.
Bamboo for foundations
In earthquake areas, bamboo's flexibility makes it a good choice for construction of a frame for floors, walls, and roofs. Such a frame may then be finished by weaving bamboo to form the solid parts of the building, or by using other materials such as clay, mud, or thatch.
Use only whole culms. Cut off and discard the upper, tapered ends of each culm so that all shafts used will have uniform thickness and strength.
The design of a bamboo frame is simple:
Begin with corner posts firmly planted in the corners set out at the site. Next, attach joists (horizontal culms that will support the floor and roof). Then attach studs (vertical culms that will form the wall frame).
Since bamboo cannot be cut to make perfectly measured joints, the shafts must be lashed with vines, bark' or wire. The only cut that can be made is a notch or cradle-like cut that can be used at the upper end of posts to support a horizontal piece.
The culm of certain species can be split open and flattened out, making a "board". Among other uses, these boards can be laid directly on a hard earth surface to make a floor. Clay is the best soil for this purpose. It should be evenly graded (for proper drainage) before the boards are pounded into place.
Bamboo boards made by splitting large culm as shown
Another type of bamboo floor is raised 1.5-2 meters so that the space underneath may be used for storage of equipment or animals. Thick culms are used as column supports; thinner culms are flattened for the floor; and woven mats are used as floor covering.
Another type of bamboo floor
Here are two common ways to use bamboo for walls:
· Wide bamboo shafts are lashed horizontally to both sides of vertical hardwood posts. Occasionally thick bamboo posts are used instead of hardwood posts. The spaces between the bamboo shafts may be filled with mud, mud and stones, thatch, or more bamboo.
The spaces between the bamboo
· Sprung Strip Construction. Vertical bamboo shafts are woven around three horizontal poles. The frame is then covered with plaster on one or both sides.
The frame is covered with plaster
Partitions may be made exactly as walls are but with lighter, portable frames. Use the lightest species available. Crack and flatten the shafts; then weave them into mats that can be suspended.
For practical reasons, doors and windows are kept to a minimum in bamboo housing. Doors tend to be made of:
· wood; or,
· bamboo matting woven on a bamboo frame; or,
· bamboo "bars" put up in a gate-like fashion.
Bamboo for doors
Windows are usually unscreened and covered with bamboo matting or a palm leaf. They can also be made out of a row of shafts tightly pressed and bound together by pieces of wood: this kind of window, when raised, acts as a shade.
Bamboo for windows
Bamboo is used for the frame of the roof. The roof covering can be of several materials:
· grass thatch;
· corrugated metal or asbestos;
· bamboo tiles made from halved culms.
Bamboo can be used to increase the strength of concrete by 2 to 3 times. To be effective, the shafts must be "seasoned" - dried out and shrunk for a month or more and then split in half.
The placement of the shafts is the same as the placement of iron reinforcement rods (see the section on reinforcing concrete, page 137).
The following simple steps will lengthen the useful life of bamboo:
· Cut the shafts at the base and store them upright in clumps in a dry, sheltered place. Never store bamboo out in the open or expose it to rain or dampness: it may rot or be eaten by insects.
· Dust the ends of each shaft with a mixture of 1:20 DDT to talc (or other, safer insecticides where available and effective).
· Use pegs to keep the ends off the ground.
· After 4-8 weeks of drying, trim all twigs and leaves off the shafts and dust the newly cut surfaces.