Monthly Archives: August 2017
Reluctance to use bamboo is rooted in the absence of design standards and unpredictable performances.
Where do we source design ideas from? Today it is common to check the internet, books and may be a few buildings around us, generally creating buildings with a modern appearance.
Countering these trends, though occasionally, we get to see newly built traditional structures. They are contemporary, yet are traditional as a cultural expression. In many ways they perform better, functionally and climatically. The Nagaland style tourist facility under construction at Puri beach is a proof for both.
Naga bamboo is straighter than the local, besides being stronger thanks to its thicker outer shell and smaller central hole. It has nodes at shorter intervals with strong diaphragms. These average 5-inch diameter culms are being used for all structural purposes, while the rest of non-load bearing members are from Orissa itself.
Selection of bamboo is the most important, with every culm treated to reduce sap content. Lengths with signs of cracks are used for slicing and splitting, Split bamboo is commonly used as walling material, weaving it between the vertical bamboo frame to gain strength and reduce porosity.
Subsequently, mud mixed with hay or grass, stabilised soil cement mix or regular mortar can be applied on the surface. This kind of walling is also called as wattle and daub method.
The floor base has to take live and dead loads, so it is made of thin bamboos laid in close proximity with floor joist members, at 2 feet spacing. The final floor finish could be with mud grass mix topped with cow dung, wooden planks, cement oxides or even layer of local thin stones. The ceiling too may have the interwoven split bamboo appearance, but factory finished bamboo matts are now available as a ceiling finish.
Roofing is among the more critical decisions in bamboo architecture. While the support system could be same as for floor, the final roof has to be appropriate.
Due to the possible unevenness of bamboo, direct placement of interlocking Mangalore tile is difficult.
So, thatch, metal sheets, ferro-cement and such others can be tried. It’s better to keep the roof angle steep, for both structural stability and faster rain runoff. In Puri, they are using local paddy straw which has shorter life, but it’s economical and easily replaceable.
Being wider at the base and thin at the top, round bamboo can be tricky in achieving uniform sizes and well secured joints. It is vulnerable to cracking and splitting, which of course, can be managed by experts. They would also know how to avoid getting harmed by split edges, sharp tips, peeling of skin and such others.
However, professional reluctance in using bamboo does not come from issues like the above. It is rooted in the absence of design standards and unpredictable performances, dependent upon species and location. But if we see how bamboo has lived with us for generations, it’s our duty to give it due regard.
The overall design of a bamboo structure is not complex, we only need to shed ourpre-conceived notion.
When we see a great work of architecture, it is worthwhile to wonder how such unique construction, style and the building method itself evolved. Typically, we attribute it all to the new generation of qualified engineers, builders and architects. In contrast to these, we also see how the traditional knowledge transmits from generation to generation, possibly improvising the idea each time.
The new visitor facility along the sea beach of Puri town in Orissa is a case in point. A Nagaland-style structure is being built there by Naga craftsmen, with Naga bamboo. The super-structure recently got completed, showcasing how it is built, an ideal time to understand building with bamboo.
Critical thought has been given to the foundation, made in concrete to withstand beach conditions with the bamboo culms embedded into the well ring mass concrete. This also gives the necessary rigidity at the foundation level to reduce the swaying of the structure in wind.
Bamboo is used for all columns, beams, floor joints, diagonal ties, bracket supports and lintels. If single units suffice for a support or beam its fine, but the hall being large single bamboos lack the required strength and load carrying capacity. So, all structural elements are in composites, i.e. multiple bamboos tied together without touching each other, but with one bamboo space in between. Small bamboo pieces are used as spacers.
Cross members are inserted into the gap between bamboos such that column and beam start to act like a single load bearing entity. Diagonal ties are very important in bamboo buildings, which help in creating equilibrium between the horizontal and vertical members, also avoiding sideward swing. Wooden members can be joined at the same alignment, but bamboos cannot. They need to overlap each other and tied together.
Multiple bamboos in one joint is a visual delight, but care should be taken to maintain the alignments, besides proper load carrying junction between any two. Since the location of members shift, so too can the centre lines of plan grid itself. To avoid it, columns are maintained in the same position, with beam members slightly to the left or right of the column bamboos.
Traditionally, thinly split bamboo peels, reeds, jute and such others were used to tie the members, but nowadays long nuts and bolts are becoming common. These bolts need to be cut and threaded to the required length, with rust proof coatings. While drilling the hole for the bolt, bamboo should not get split. It is observed that nut and bolt system may go loose in case of vibration due to heavy footfall, widened hole size or bamboo with more sap content than prescribed. Incidentally, Naga bamboo with thicker outer shell is less vulnerable to this problem.
The overall design of a bamboo structure is not as difficult as people talk about, but are very basic in nature. We only need to shed our pre-conceived notions about bamboo.
It was ideal housing material for long but had lost favour in recent times. However, bamboo is slowly making its mark again.
When an ecologically appropriate material finds less users, it is time to think. What makes the modern, energy guzzling material ride over the ecologically sensitive one? Equally well, if that material regains its popularity, it is also time to think. What brings about the green sense again?
Bamboo could be an apt example to this trend. Actually a grass, it consumes less primary energy than wood; assimilates more carbon dioxide for photosynthesis than trees, ensuring faster sequestering of carbon; reduces soil erosion due to its thick root formation; and produces more bio-mass per hectare than many other plants with its rapid growth.
An easy to transport material with surface tensile strength higher than steel, bamboo is best among the light weight construction options, where speed of execution is required. It sways with flexibility, hence does not break against fast wind; it is not a rigid construction, hence does not collapse during earthquakes; it grows very fast, hence becomes a rapidly renewable resource; and the culm can be used all through its thicker lower parts, thinner upper parts and the sliced surface.
Majority of construction techniques require externally erected scaffolding systems for holding the materials and workers, with larger buildings demanding cranes.
Building with bamboo needs all these minimally, with expert workers using the built part itself as the support. Even though construction happens part by part, once completed the building appears singular and interconnected.
Yet, the execution does not lead to a monolithic construction, which is in favour today. The concrete, ferro-cement and modern organic forms appear monolithic in their final version.
Even the simple brick wall houses we do have a dozen RCC columns with walls plastered and painted to hide the individual masonry units, though they drain the money and strain nature. Bamboo architecture is neither monolithic nor hidden, which is actually its strength, not a weakness.
Bamboo has been best suited for thatch roof, country pan tiles, slates and stones, which can be comfortably fixed despite the slight unevenness of the canes. As roofing materials gave way for interlocking and overlapping tiles like Mangalore tile which demand perfect levels, bamboo lost favour. Coupled with the increasing popularity of RCC roof, bamboo slowly got relegated to the back benches.
In the past, housekeeping and maintenance was part of living in the house. Today people expect that the building be maintenance free, a pre-condition which rules out too many eco-friendly materials and construction types. Bamboo too is a victim to this trend, which cannot be cleaned all around, polished frequently or left exposed to sun and rain once built. As skilled labourers dwindled, popularity of bamboo also waned.
Promoting the cause
But slowly but steadily, bamboo is again in the reckoning. Internationally, books on bamboo are increasing and the one by Gernot Minke proves the value of the material so simply and directly. Vaibhav Kale, Sanjay Prakash, Neelam Manjunath, Uravu group, Sanjeev Karpe, Saajan and many more have been promoting it in their own ways. Bamboo has a future again.