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Your local material in construction

Reluctance to use bamboo is rooted in the absence of design standards and unpredictable performances.

19bgp-greensensGVG2AC0VV2jpgjpgWhere 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

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

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.

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There is beauty in bamboo

The overall design of a bamboo structure is not complex, we only need to shed ourpre-conceived notion.

12bgpgreensenseG58293FDE3jpgjpgWhen 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.

Visual delight

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.

The Bamboo Revival

It was ideal housing material for long but had lost favour in recent times. However, bamboo is slowly making its mark again. 

05bgp-greensensGMF27NT5P3jpgjpgWhen 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.

Core strength

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.

BAMBOO PAVILLIONS

Bamboo pavillionTravelling to far off places opens our eyes and options exponentially, and makes us apply the new learnings locally, back home. From this perspective seeing houses completely built with bamboo can be an exciting proposition and there are many of them in varied regions of India. However, suddenly jumping into the dream of doing a bamboo house in Bangalore or Chennai will not be easy. Local materiality and construction practice always holds fort and discourages new ideas from pouring in.

In such cases, introducing bamboo step by step, slowly expanding to more elements could be an easier way out. Since we have extensive bamboo constructions as a proof for their performance, even in heavy sun or rainy regions, having some certain building parts may not become a bothersome issue. Of course, proper treatment with Boric acid Borax solution or gentle burning or seasoning with flowing water and such other measures for reducing the sap content, to keep it well seasoned is a pre-requisite. Also, we need to follow basic code of practice like avoiding poles with visible splits and such others.

Pavilions are amongst the easiest to start with bamboo in any building. Like any other roof, it needs column support done with 6 inches or larger diameter poles, or if spans are longer, we may use structural steel as advised by the engineers. Such members can even be wrapped with bamboo peels skinned from its outer surface to give the looks of bamboo. Machine pressed bamboo mat, hand woven mats or local regular mats could be used as ceiling finish, supported on split bamboo. Thereupon, coated G.I. sheets, water proof thick plastic or any other metal roofing can be laid to ensure protection from rain. Incidentally, traditional homes achieved it without metal anywhere!

The top is finished with small bamboo poles or sometimes, with half split bamboo laid with the curved part upwards. When tin sheets became popular, they replaced the bamboo top, considering complete bamboo roof is more cumbersome and maintenance heavy when it comes to rain protection. However, they deny the bamboo looks – an aspect many people prefer to see, hence the idea of composite roof with both sheets and bamboo. Being lightweight roof, bamboo pavilions need lesser cost for support members.

Bamboo members should not run across the slope, obstructing the flow of rain water. Point of contact between metal inside and bamboo top can hold water dampness affecting both the materials, hence pre-treatments are mandatory. The mat between the rafter supports may sag as people work on it or by age, hence proper spacing should be maintained between the supports.

The pavilion idea can be easily extended into a room itself with bamboo pole flooring support, floor finish of one’s choice, better security and rain protection. If we have the desire to start with bamboo, it is not difficult to end with a bamboo house.

CLIMBING THE BAMBOO STEPS

Bamboo stairsWould we believe in the statement ‘some of the newest ideas are based on the oldest practices’? On the face of it we may not, but if we look at the way bamboo is making a grand return, most of us may agree. As we are searching for new ideas of design and solutions for ecofriendly living, we realize the past holds as many inspirations as the future can tempt us with.

The long lengths, jointed body, light weight, easy workability and such others made it an excellent material for high walls and roofs. With a surface skin that can be easily peeled, bamboo provided varied products like woven baskets and floor matts. With a tensile strength beyond that of steel, it found popularity as supports for buildings and pavilions. At the other extreme end, bamboo shoots provided unparalleled options in food too!

People have climbed on a bamboo ladder ever since they lived in settled societies, especially in areas where bamboo grows. In the basic form, one would cut off the small branches leaving only a small part of it, such that they work as steps at staggered levels. This way, people could climb on a single bamboo pole, if it stays stable against a support and carry it around with ease. Then came the design with two poles interconnected with the steps, so one could get better hand grips and stability for the ladder itself.

However, bamboo did not go beyond this stage in a big way, where wooden and later concrete staircases dominated. But let us imagine a bamboo stairs just the way steel framed stair works – we get two inclined members on both the sides, they support the horizontal base, bamboo board is fitted to the base and the sides secured. There could be a riser member or we may drop it to get an open riser design. If a sturdier tread is desirable, the bamboo board can be placed on a thicker ply base. The railing can rise from the inclined side supports.

The major disadvantage of doing a bamboo staircase lies in handling the material, demanding both practice and skill. While nails can be used, they tend to go loose after some time; hence nuts and bolts perform better. To that end, proper holes have to be drilled and nuts properly tightened. However, traditionally no metals were used; instead poles were secured into each other through cuts and ropes made from bamboo itself. Considering that Bamboo comes in varying sizes, this method appears to be more effective.

If regions like Assam can live on bamboo staircases, Bangalore too can live on them. They combine beauty with functionality; cost efficiency with longevity and provide visual tactile feel of a very different kind. Doing a complete building in Bamboo may be difficult in non-bamboo regions, but integrating it within the parts and elements of the structure is definitely doable.

Climbing the bamboo steps

If regions such as Assam can live on bamboo staircases, Bengaluru too can live on them. They combine beauty with functionality.

06PP--greensens_06_2429559g

Would we believe in the statement ‘Some of the newest ideas are based on the oldest practices’? On the face of it we may not, but if we look at the way bamboo is making a grand return, most of us may agree.

As we are searching for new ideas of design and solutions for eco-friendly living, we realise the past holds as many inspirations as the future can tempt us with. The long lengths, jointed body, light weight, easy workability and such others made it an excellent material for high walls and roofs. With a surface skin that can be easily peeled, bamboo provided varied products like woven baskets and floor mats. With a tensile strength beyond that of steel, it found popularity as supports for buildings and pavilions. At the other extreme end, bamboo shoots provided unparalleled options in food too!

People have climbed on a bamboo ladder ever since they lived in settled societies, especially in areas where bamboo grows. In the basic form, one would cut off the small branches leaving only a small part of it, such that they work as steps at staggered levels. This way, people could climb on a single bamboo pole, if it stays stable against a support and carry it around with ease. Then came the design with two poles interconnected with the steps, so one could get better hand grips and stability for the ladder itself.

Didn’t go further

However, bamboo did not go beyond this stage in a big way, where wooden and later concrete staircases dominated. But let us imagine a bamboo stairs just the way steel framed stair works – we get two inclined members on both the sides, they support the horizontal base, bamboo board is fitted to the base and the sides secured. There could be a riser member or we may drop it to get an open riser design. If a sturdier tread is desirable, the bamboo board can be placed on a thicker ply base. The railing can rise from the inclined side supports.

Disadvantage

The major disadvantage of doing a bamboo staircase lies in handling the material, demanding both practice and skill. While nails can be used, they tend to go loose after some time; hence nuts and bolts perform better.

To that end, proper holes have to be drilled and nuts properly tightened. However, traditionally no metals were used; instead poles were secured into each other through cuts and ropes made from bamboo itself. Considering that bamboo comes in varying sizes, this method appears to be more effective.

If regions like Assam can live on bamboo staircases, Bangalore too can live on them. They combine beauty with functionality; cost efficiency with longevity; and provide visual tactile feel of a very different kind.

Doing a complete building in bamboo may be difficult in non-bamboo regions, but integrating it within the parts and elements of the structure is definitely doable.

Bamboo needs our support

It is good news that there are now increased attempts to develop a widely acceptable Indian standard code for bamboo, which will help promoting its use.

14HAB-Bamboo_GP_14_1583868eWhere does India stand in world rankings in bamboo cultivation? It’s an answer we can be proud of – we are second, next only to China. The extensive tropical region in our country enables this production and is climatically suited for its usage also. As such increased production, easy availability and regular supply can be assured for bamboo, except in few regions.

Where does bamboo last longer, thanks to local climate? Again India – extreme temperature and humidity variation reduce the life of bamboo, but in most areas of India with moderate temperature variation, bamboo can last long. All this to confirm that India is ideally suited for bamboo buildings.

Bamboo needs three to five years to grow to maturity, by when it can be cut for construction though the basic height could be achieved in six to nine months. Even without any treatment, it can perform well beyond six years, but with minimum maintenance, many village bamboo structures have lasted beyond 20 years. Of course the best is to artificially treat it, to reduce termite attack, dry and wet rot, surface water penetration and such others, thereby ensuring durability and extended life.

Treatment

The most common bamboo treatment is dipping the culms in a solution of 2 kg boric acid and 3 kg borax dissolved in 45 litres of water for two to three days, tank especially made narrow and long to fit the bamboo poles. Copper Chrome Boron solution with pressure impregnation method is also possible, where necessary facilities are available.

Among the recurring questions on bamboo building is costing. It is difficult to arrive at a standard cost, but budgetary range for the proposed construction can be suggested by subject experts. However, this should not be directly compared with conventional methods to arrive at the lowest quotation and work awarded to a contractor.

The public sector uses standard schedule of rates for tendering projects, wherein bamboo will not find an easy place. It is good news that there are now increased attempts to develop a widely acceptable Indian standard code on bamboo, which will help promoting its use.

There are many individuals and organisations passionately working towards a better future for this material such as Wonder Grass, IGBMT, IPIRITI, Laurie Baker Building Center, INBAR, and Bamboo House India. Despite their dedicated efforts, the larger part of India’s production goes for paper making.

A notable quantity is used for non-construction items such as crafts, basketry, daily use items, and woven forms like screens and mats.

While such a wide use is laudable, it will be good to see an equally wider use in construction industry, for a greener and sustainable future.

The challenge in using bamboo has been our mindset than the material itself, though in certain areas it may not be feasible for varied reasons. If we can introspect why we are not using bamboo, we may realise our misconceptions and relook at this wonder grass.

  • Bamboo needs three to five years to grow to maturity, by when it can be cut for construction, though the basic height could be achieved in six to nine months.
  • Treat bamboo artificially to reduce termite attack, dry and wet rot, surface water penetration and such others, thereby ensuring durability and extended life.
  • Even without any treatment, it can perform well beyond six years, but with minimum maintenance, many village bamboo structures have lasted beyond 20 years.

From foundation to roof

There are many valid reasons to use bamboo in construction which need to be explored further. 

07bgp-bamboo_G7_07_1576423eBetween bamboo and structural steel, which one has more strength? Which one will perform better in case of deep soil pile foundation? If left open without any protective coat, which one will last longer without rusting or withering? Which one has more options of application and is versatile enough for wall, column, beam and floors?

The surprise answer for all the above is bamboo. At an average tensile strength of 12,500 kg/sq. in., it is 2,000 kg units more than that of steel. The stems of bamboo, popularly called poles and technically as culms, have been traditionally used for pile foundation in water-logged and loose top soil sites. Bamboo mats can be laid as foundation bed in case of soils with low load-bearing capacity. As a versatile material, it is good for both temporary and medium term usages, besides for long term, if designed and built properly.

While bamboo can be used as a single pole, it works equally well in groups and as a composite material. For transferring heavy loads, multiple numbers of culms, say 3 or 4, can be joined by nuts and bolts to act like a single column. Likewise, it is possible to form beam trusses in groups or in lattice formation. Of course, all the bamboo poles in such composite forms need to belong to the same species, of similar girth and be of comparable maturity of age.

In Kerala, lime concrete bamboo reinforced beams have been attempted since the late 1990s and in regular use since then at the Laurie Baker Centre. While stand alone use is feasible, bamboo gains more potential as part of a composite structure and reinforcement material.

Traditional walls

The traditional bamboo walls were made with woven bamboo mat with mortar coats on both sides, so that bamboo is not exposed to any adverse weather condition. While lime and mud mortar goes better with the natural material, cement mortar can also be used. Subsequently, protective painting coats can be applied. Being 2 to 3 inch thick, they are light weight, hence save on structures. If split bamboo culms are used, keep them to the outside with inside finished as desired. External silica-based skin of bamboo resists fire for a while, but can be improved by chemical coatings. Bamboo boards with split lengths and panel are very popular as visual barrier in semi-open spaces like verandahs and pavilions.

Roof supports by bamboo rafters are very commonly found even today. Thicker girth culms are used as ridge beams or wall beams, while the smaller diameter ones can go for principal rafters in sloping and cross beams in flat roofs. Their spacing may vary from 1 to 2 metres depending upon context. Floor finish can be achieved by 1:6 ratio lime mud or cement mortar with topping by floor tiles and any other item of choice. There are many valid reasons to use bamboo, which need to be explored further.

Handling bamboo

The criteria to assess bamboo structures cannot be the same as those for timber, masonry or modern buildings.

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Often we get to see a many-decades-old tiled house being replaced by a new RCC-roofed house. The chances that the old house roof was supported by bamboo rafters is very high. Repeatedly coated with cashewnut oil in coastal areas, hence surface protected, these rafters would have hidden their actual age. The north-eastern States virtually live with bamboo – pile foundation, support pillars, floor sections, wall mats, roof supports, window frames, objects to live with and such others. Despite all this, we feel bamboo is a mere local temporary material.

Possibly, the myths about bamboo have come to stay due to the wrong way of using them. Any bamboo, however mature it is, if left to the vagaries of rain and sun untreated, will not last beyond a few years due to the high starch content. Local methods like cashew oil coating cannot be replicated everywhere and not everyone keen on using bamboo is aware of other treatments. People tend to think bamboo is cheap, which is not a fact always; hence discard the idea without looking at the value for money. Bambusa Arundenesia and Dendrocalamus Strictus are better suited for construction, yet we tend to use whatever is locally available and then blame the idea of building with bamboo itself. No wonder, though India is the second largest producer of bamboo in the world, most of the production goes to the paper industry, daily use objects, screens or temporary supports for construction.

Simple method

The common comments against bamboo revolve around it being a fire hazard, which is partly true. However, the high silica contents of the surface wards off fire for longer time than timber and fire-proof chemical coatings can improve the performance comparable to any other material. The wall panels of bamboo are rather thin, just 2 to 3 inches only; hence do not assure sound-proof qualities.

Bamboo mats can be enmeshed within cement mortar, a simple method that improves both its fire retarding and sound-proofing qualities, but this has to be done carefully. Incidentally, all bamboo buildings require skilled workmanship and good working knowledge of the material. The joints can be very tricky, cut sections demand careful handling, while grooves, ropes and knots need to be complimenting the overall structure.

It is easy to justify why bamboo should be used. We can list reasons like economical in regions where it grows, lighter weight for the dead load calculations, faster in construction, faster re-growth of cut bamboos, hence regeneration of the material and such others.

However, the criteria to assess bamboo structures cannot be the same as those for timber, masonry or modern buildings. If we apply different yardsticks, case by case, then bamboo buildings will also get as accepted as are other mainstream buildings. To that end, we will have to follow the proper methods of building with bamboo.

Building with bamboo

This wonder grass has more tensile strength than mild steel, in given specific conditions, and can bear heavy construction loads too if used correctly.

24HAB-greensens_24_1561117eIn all fields there are great potentials, unfortunately lying hidden waiting for their day. There are solutions that go unnoticed and unsung. Leave alone mainstreaming them, even recognising them to ensure larger public acceptance becomes a challenge. In construction, such ideas could be region specific and not universal, material specific and not for every kind of material, and knowledge specific and not for casual application.

Bamboo fits into the above background note more than any other construction material around. Hailed as wonder grass by the experts, it is a plant material that matures for construction purposes approximately in six years, possibly the shortest time span of its kind. Though bamboo has proven its potential across many regions in the world, it does not grow everywhere; hence it is not known as an option outside its habitat. Even if known, majority of people believe that bamboo can be used only for structures of minor importance and temporary in nature, which actually is a myth. Widespread usage of all types of bamboo, especially in untreated conditions, has led to this judgment.

Across Indian regions, there are hundreds of varieties of bamboos; Kerala alone has more than 130 types. Not all of them are best suited for building construction, with less than 10 varieties satisfying the checklist of criteria. Choosing the right type of bamboo is of utmost importance in ensuring the right kind of building. This requires studied knowledge and skill, for in the market all of the stock may look alike. The best method of course is to check out bamboo grove supplying the material and ensure the particular grove has the shortlisted bamboo type. The cut bamboo should not have flowered and should not be aged, when it would have had reduced strength. What if we end up using some bamboo not knowing if it is the best or not? There would be no disaster, but the durability, maintenance, load-bearing capacity and such others may not be very satisfactory.

Standing tall

Bamboo has more tensile strength than mild steel, in given specific conditions!.While living and standing tall, bamboo may swing in the wind violently, but takes the wind load very well, suggesting its hidden load-bearing capacity. Its fibrous structure ensures a shear-proof material that can transfer vertical load efficiently and diagonal loads fairly well. Without cutting equipment, it does not get cut into parts by hands, rain and wind. The unique structure of bamboo ensures material integrity, minimum water penetration across the skin, longer life than timber even if left exposed to weather, light weight for its given volume, and ease of working with, thanks to the manageable sizes.