GCR caught up with the lead author, Dr. David Trujillo, assistant professor at the University of Warwick, to ask how.
What materials do you think bamboo could replace, and why?
DT: There are two parts to my answer. Engineered bamboo, which is a bamboo product obtained through processing it into timber-looking sections, can replace hardwoods very readily. However, engineered bamboo is outside of the scope of our manual.
In terms of bamboo in its natural shape, it cannot readily replace a given material, but by taking a different approach, it can replace them functionally.
For example, we can make a bamboo-based wall system, called “composite bamboo shear walls” (CBSW), that can replace masonry in one and two storey housing very effectively. CBSW is a technology originating from Latin America that is described in the manual. It’s an evolution from wattle-and-daub and is similar to what North Americans call stud-frame, or light timber frame and in the UK we call platform timber frame. The differences are that we replace some of the framing elements with bamboo and the board products with a matrix containing a range of materials including cement mortar render.
Composite bamboo shear walls (Image courtesy of Base Bahay Foundation, Inc)We can also make roof structures that can replace timber and steel and produce very beautiful structures in the process.
However, I reiterate, it would not be a direct substitute for these materials. We have to adopt bamboo-specific structural forms.
How can bamboo be used alongside other materials?
DT: No material can do everything. Like all materials, bamboo works best when complemented by other materials.
The systems contained in the manual require using metal in connections and we used cement-mortar and timber to compliment bamboo framing elements in CBSW systems.
You would need other materials in order to make roofs waterproof.
There are 1,600 known species of bamboo, are certain species useful in different methods of building?
DT: Out of the 1,600 species or so of bamboo, probably only 100 are of use for construction and, of those, maybe 20 or 30 have been studied in some depth. Obviously there’s a lot of scope to use more species and explore their qualities.
It is very interesting to see how people combine species to achieve the desired effect. In Bali, they like combining different species with different colours and sizes, resulting in very beautiful structures.
We believe that you need the larger bamboos, 50mm or even 100mm in diameter, for structural applications, but smaller bamboos can fulfil other construction purposes, even if only decorative. However, at present, people tend to be limited by availability, meaning species that are locally abundant.
Are there other less widely used materials that you think can be adapted for construction?
DT: There are many interesting natural materials that are not deemed mainstream despite having been used for millennia. Our manual focuses on bamboo, but undoubtedly there are more to explore.
One of them is earth. It makes a lot of sense to use it because we always have it below the building and we return it at the end of the building’s life.
There are other bio-based materials that are very worthwhile like straw and hemp, as well as numerous species of trees that have been ignored but that have potential due to their fast growth. Bamboo is just another material from the palette of super-low-carbon materials.
How can contractors and clients be encouraged to use alternate materials like bamboo?
DT: I think a great deal about how to make materials like bamboo more mainstream. We all have a role to play. A lot more funding for research and development of seemingly “vernacular” materials is needed.
Unfortunately, many funding calls focus on the “latest”, “super-high-tech” technologies. The most low-carbon technologies are hiding in plain sight. Pre-industrial materials are by definition low-carbon. They simply need to be revisited, modernised and upscaled.
We need governments to help get these materials accepted in the building regulations and construction codes. We need universities to decarbonise the curriculum. We cannot continue teaching students of engineering and architecture solely how to use steel and concrete. We need to prepare future professionals for these low-carbon materials.
Insurance companies and banks must see that their risk aversion has a carbon footprint. Every time they reject a low-carbon material, they force the world to adopt high carbon-materials.
Finally, we need the supply chains to flourish, but people are not going to invest in companies that can’t sell their products.
What about fire risk?
DT: Bamboo is combustible but not highly flammable like some regularly-used foams and plastics. Combustible materials require precautions during construction and in design. In the manual, we have limited the scope for bamboo in its natural form to two storeys in order to control the fire risk.
The manual also provides guidance for fire considerations in design.
Overall, known techniques for working with combustible materials are transferrable to bamboo, for example encapsulating bamboo behind another material like plasterboard. It should be noted that engineered bamboo performs better in fire because it’s not hollow.
This is why we need future engineers and architects to understand the material so that they know how to use it to make it a safe structural system.
How durable is it?
DT: As a bio-based material, bamboo is biodegradable, which means nature has a way to dispose of it. To make buildings durable, we need to stop these natural processes. If we keep bamboo dry and ventilated to prevent fungal attacks and incorporate chemicals to prevent insect attacks, it has been proven to last for decades.
If we expose bamboo to moisture and the sun, durability is significantly compromised.
How likely is widespread bamboo adoption in Europe?
DT: I think bamboo will be used differently in Europe than in Asia, Latin America and Africa. This is in part because bamboo used in the tropics is much larger, but also because using it in its natural shape involves more labour during construction.
In the near future, Europe is more likely to use engineered bamboo, transformed into timber-looking products, which is easier to use and can act as a timber substitute. For a while, these products will need to be imported into Europe until the economies of scale justify a European domestic industry. Some organisations are already investing in this.
It should be noted, that the carbon footprint of importing engineered bamboo products is relatively small and the upside is that we would help foster these industries in the tropics, creating job opportunities where they are desperately needed.
What’s bamboo’s role in more tropical regions?
DT: It has been estimated that most construction in the next decades will take place in Asia, Africa and Latin America. If those regions go down the high-carbon path, it will be disastrous for carbon mitigation. Bamboo should play a role in decoupling urbanisation from carbon emissions. We can use bamboo in its natural shape for housing, schools, community centres and other single storey commercial or industrial applications.
Engineered bamboo could be used for larger constructions such as multi-storey buildings and possibly footbridges.
We can then reserve concrete and steel for those things that really need it: skyscrapers, vehicular bridges, infrastructure, foundations and retaining walls.
How does building with bamboo impact the size and shape of structures?
All materials have optimal applications and shapes. In its natural form it performs best in compression and moderately well in bending. It theoretically could work very well in tension, but current connection technology limits this.
Therefore it works well making arches and what I call “fan-shaped” trusses, which are displayed in the manual in more detail. With this in mind, you can see it working very well in halls and gymnasia.
It also works well for applications with moderate spans, such as residential applications. It is challenging, albeit not impossible, to use in footbridges.
The manual, titled Manual for the design of bamboo structures to ISO 22156:2021 is available to download for free.Further Reading:
Bamboo firm wins €250,000 bio-material prize Bamboo housing for the elderly would be cheaper, faster and greener Floating bamboo house can halve its size to cope with any disaster Ramboll & Friends to create high-tech, disaster-proof bamboo housing for IndonesiaHow bamboo can help decouple urbanisation from carbon emissions Global Construction Review.
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