Bamboos are a group of both woody and herbaceous plants in the grass family that are classified as non-wood or non-timber forest products. They are grouped into over seventy five genera with more than one thousand two hundred species growing worldwide. They belong to the family poacea, subfamily bambusoidae, and the tribe bambusae. Bamboos are multi-purpose crops having more than 1,500 documented uses the world over. There are over thirty eight priority species in the world with ten being used predominantly in construction related applications. The bamboo trunk is called a culm and is the one that is mostly utilized in construction, although the leaves can also be utilized as thatch.
Bamboo is common in the tropical climates of the world. Most of the bamboos are found in Asia which has a total of 992 species; Africa is at the lower end with only 50 native species. The most predominant species in East Africa is Yushania alpina which is also the only native species found in Kenya. The other species common in Kenya is Bambusa vulgaris (variegated) which was brought in from Asia and is used around the country for ornamental purposes in landscaping. Europe has no record of native bamboo growing; the first bamboo to be introduced to Europe was in 552 AD and was taken there by monks from Asia who used it to smuggle silk worms to Europe.
Historical use of bamboo in construction
Traditional bamboo construction can be referred to as one that existed before intervention by architectural or engineering professionalism, whose skills were passed down from generation to generation; it incorporated bamboo in its raw form albeit with little transformation like splitting that needed no specialized techniques or tools. Bamboo has been used in many parts of the world in construction; In Indonesia by 1956, 35% of the houses were exclusively made out of bamboo while 35% were a mixture of bamboo and wood (UN 1956). 60% of houses in Bangladesh and Burma were made out of bamboo (McClure, 1945) and in the Philippines 90% of the houses were made out of bamboo. In China bamboo has been used as scaffolding for thousands of years. Traditional uses of bamboo in construction can be classified as follows:
- Form of use: Bamboo can be used in many different ways, the traditional builders used it in four distinct ways: whole culm, woven bamboo, split bamboo and flattened bamboo that was used as floor matting or walling.
- Place of use: Bamboo was used in every building component as fencing, walling, flooring, and as structural support in the form of stilts, beams and columns. It was also used for roofing as thatch and bamboo tiles where the culms were cut at the nodes and then split into halves similar to half round ceramic ridge caps; they were then laid on the roof in an alternating upward and downward facing pattern.
- Climatic response: Different technologies evolved in the use of bamboo regarding the climatic conditions of a given place. In Ecuador for example, bamboo matting was used on the walls to allow for cross ventilation due to the hot climate.
- Joinery techniques: The three basic joinery systems were the fish mouth (fig 1), the through joint and the lashing technique using ropes (fig 2). The main tool used was a knife.
5.Material combination: Many communities used bamboo in combination with other materials like thatch on the roof, mud plaster, rammed earth and wood mainly as reinforcement.
6.Preservation techniques: Bamboo is prone to fungal attack when in contact with moisture and also attack by the powder post beetle, traditional bamboo architecture responded to these by: avoiding contact of bamboo structures with soil by building them on platforms, harvesting of bamboo was also done during the dry season, when starch and moisture content was very low. Some communities believed that bamboo should be harvested very early in the morning during full moon as they thought that bamboo would not be attacked by beetles then. Science proves that moisture content in bamboo increases from full to new moon thus validating this theory.
The Dorze community of Ethiopia built a tall (about twelve meters in diameter and height) beehive shaped woven bamboo house, when the part of the house that was buried in the ground rot, the hut was lifted and shifted to a different place. This was repeated several times until the house was too small for habitation.
By comparison, the Adi Gallong, a community found in Siang District of Arunachal Pradesh state in India and a hill dwelling, used smoke and heat in preservation of the house. They had a permanent fire within the house that was constantly lit; the smoke served as a preservative to the bamboo. The other aspect of preservation was the roof which was very low and had a big overhang that covered the verandas hence keeping off water that is a major agent of decay in bamboo. The houses were also raised on stilts for the same reason. In the planning of the house, a washing area was provided; this was protected from rot by leaving large gaps in between the split bamboos at the washing area for proper drainage. Woven bamboo matting was used on the floor, giving different texture finishes for different areas, depending on use. For example, where the firewood was kept was course textured.
In Japan, bamboo was preserved by smoking; however bamboo smoke was obtained by burning pieces of bamboo in a kiln. Bamboo smoke contains pyrolitic acid that is believed to be very effective in preserving bamboo. During the construction of the ZERI pavilion in Hannover Germany to showcase sustainable architecture, the architect Simon Velez used this technique of preservation.
Contemporary uses of bamboo in construction
Bamboo can be used in any part of the building, be it the structure or the normal architectural elements like the walls. In 2009, Andry, W and Martin Trautz classified modern bamboo construction into two: substitutive and conventional, the former referring to use of bamboo to replace other materials and the latter to the use of bamboo without varying much from its use traditionally e.g. by using bamboo whole culms for column construction albeit with few improvements like bolting for joinery instead of the traditional lashing. These two classifications are further subdivided into the individual building components that can be used when constructing with bamboo. Traditional conventional bamboo construction has been evolving resulting into engineered bamboo construction. Bamboo can be used in the following ways:
- Structural uses: these include columns, beams, roof trusses and scaffolding.
- Walling: this can range from split bamboo culms, flattened bamboo and even whole culms
- Roofing: found as engineered bamboo, as well as thatch bamboo and split bamboo tiles
- Flooring and ceiling finishes
- Windows and doors
Bamboo construction in Kenya
In Kenya, bamboo construction has not really taken off yet; however there are efforts to integrate its use in the built industry. Two demo houses exist at Maseno University. These were put up in collaboration with the International Network for Bamboo and Rattan (INBAR) in 2009 to be used as showcase houses for the local people on how to utilize the bamboo harvested from the neighboring farms. These houses are: 1) the engineered bamboo house, and 2) the non-engineered bamboo house. These houses employed different construction techniques. Engineered bamboo is a product designed to function as conventional timber. The engineered bamboo house comprised of an engineered bamboo frame that was plastered. The non-engineered house was built using bamboo harvested from Kakamega Forest. Mature bamboo culms (3-5 years old) were harvested and treated using a Boron-borax solution, after which they were seasoned and used in the build. The roof structure and columns for this particular house were made using whole bamboo culms (fig 3), while the ceiling utilized flattened bamboo (fig 4)
Advantages of bamboo use in construction
- Growth rate is three times faster than eucalyptus and it conserves water
- High annual yields of about 17 tons per acre in a well managed plantation
- Bamboo matures in 4-7 years compared to other trees that take over 15 years
- Due to its lightweight, high elasticity and great resistance to rapture, bamboo is ideal for numerous construction uses, and is suitable for construction in earthquake regions.
- It is cheaper than steel and concrete, and yet equally strong
- When well treated, it is durable.
Challenges in the use of bamboo as a construction material
- Bamboo is prone to invasion from the powder post beetle due to its naturally occurring sugar, thereby necessitating treatment before utilization in construction. This treatment can be by natural preservation like soaking bamboo in water after harvesting to wash away the sugar or by chemical preservation such as the use of boron-borax to alter the taste of the culms.
- Bamboo is combustible, and should therefore be protected from fire as much as possible.
- The cost of bamboo is still high when compared to other materials available in the market.
- Minimal technical know how of the proper handling of bamboo during construction.
Possible applications of bamboo in landscape design
One of the most critical design points to consider is to protect bamboo from moisture, since just like timber extensive exposure to moisture causes degeneration and rotting. This can be done by preventing direct contact of bamboo structures with the ground and designing large roof overhangs to protect the walls from rain. Bamboo can be utilized in landscape design as soft landscaping in planters. Other uses include gazebos, shades and pergolas, outdoor furniture, hammocks, fences, screens, gates, and footbridges among others.
The use of bamboo as a construction material in Kenya is an area that needs to be explored. Integration of bamboo in the construction industry has the capacity to better utilize the existing resources thereby lowering the cost of procuring bamboo for construction.