Carbon Impact of Bamboo
Bamboo is a rapidly renewable, versatile building material. Bamboo can be used in both pole construction (as scaffolding, roofing, framing elements, and even reinforcement for concrete) and in manufactured products. Manufactured products include engineered structural components, finishes, and acoustic and structural panels. There are many advantages to using bamboo as a building material, including its superior mechanical properties (the properties that involve a reaction to an applied load1), tensile strength, elasticity, and cost effectiveness. Bamboo has a greater compressive strength than concrete and approximately the same strength-to-weight ratio as steel in tension.
While bamboo is technically a woody grass and not a tree, it is considered a Non-Timber Forest Product yet is often classified as forest or timber2. Bamboo forests perform similarly to other types of timber forests regarding carbon sequestration, though there are over 1,600 species of bamboo and the amounts of carbon sequestration vary greatly across species. One study found that one hectare of Moso bamboo, the species predominantly used in building materials, can sequester about 102-289 tons of carbon annually based on various factors which is equal to or slightly lower than other non-bamboo forest types3. 67-81% of this carbon is stored within the soil layers however.
Unlike timber forests, only 20-25% of the stalks or culms (the stalk and part of the plant that is used for building products) in sustainable bamboo forests are harvested each year (compared to 80-90% of trees harvested in sustainably managed timber forests4), and the bamboo plants do not die after harvesting, ensuring no deforestation5. Bamboo is also much faster growing than timber – some species of bamboo (i.e. the Moso species) will grow as fast as two feet in a day. Some species of bamboo may be harvested after three to eight years when the water and sugar will be displaced by stronger cellulose. Bamboo culms should be harvested within ten years; after ten years the culms will die and return carbon back into the air6.
Carbon Smart Attributes
Only specify bamboo from sustainably managed bamboo forests
Sustainable management of bamboo forests is critical in protecting the carbon stored in soil layers and increasing the carbon storage capacity in the above ground bamboo stalks. Specify bamboo products that come from sustainably managed bamboo forests and preference bamboo from forests that are natural or reforested, not created through land use change (i.e. clearing natural timber forests to be plantation bamboo farms).
Source locally when possible
Moso is the most common species of bamboo used to manufacture flooring, furniture and construction products and is grown in temperate climates around the world (i.e. China, Vietnam, and India, and now being grown commercially in the Southeast US). However, there are approximately 1,600 species of bamboo grown across much of the world in a variety of climate zones, though different bamboo species are appropriate for different building applications. Source the bamboo product as locally as possible to reduce transportation emissions.
Specify steam kiln- or air-dried bamboo to avoid fossil fuel emissions
For pole construction, bamboo poles are typically air-dried, which often takes 6-12 weeks7. Natural gas is sometimes used to dry bamboo faster, which releases carbon emissions and can increase the incidence of cracking. For the manufacturing of engineered components (both structural and non-structural), the harvested bamboo is typically kiln-dried (powered by steam fueled by waste or sawdust from the processed bamboo, others by fossil fuels) to a consistent moisture content to ensure the product does not cup, warp or delaminate. If possible, specify air-dried bamboo for pole construction. For engineered components, specify steam kiln-dried bamboo that utilizes waste or sawdust from the processed bamboo.
Material Attributes
Bamboo has a high tensile strength
Some studies have found that bamboo has a higher tensile strength than steel because its fibers run axially (along the length of the pole)8, making it a carbon smart alternative to steel rebar9 or steel structural members.
Bamboo is elastic
Bamboo is similar to wood in that its tissue structure provides its strength. However, bamboo fibers are several times longer than wood fibers and almost all bamboo fibers run the length of the culm, allowing it to bend without deforming or breaking in situations such as earthquakes or in extreme wind. Because of this, when manufactured correctly, engineered bamboo structural components, such as bamboo nail laminated timber systems, are suitable for use in earthquake prone regions as a carbon smart alternative to concrete and steel10.
Bamboo is fast-growing
Bamboo is one of the fastest growing plants in the world – three times faster than most other tree species and produces 20 times more fiber than trees. Moso, a ‘timber’ bamboo species, can grow two feet per day, reaching heights up to 80 feet in just two months11. Due to this, crop rotation cycles can shorten and more product can be harvested sustainably with no re-planting necessary.
Bamboo is fire resistant
Due to its naturally high percentage of silica content, and insect treatment with boric acid (often used as a fire retardant), bamboo poles can resist fire and temperatures up to 400 degrees Celsius8, making it slightly more fire resistant. Engineered bamboo products are typically laminated with a resin making it very fire-resistant as well.
Design & Construction Guidance
Design for durability
Similar to wood products, bamboo is vulnerable to natural elements when used in pole construction. Ensure that bamboo is properly treated prior to use and then protected during the construction process and life of the building to protect it from insects, fungus, rot, and fire.
Ensure bamboo was properly dried
Bamboo must be properly dried for long-term use with a moisture content under 20%. Ensure that the bamboo has been dried properly and without using fossil-fuels.
Acknowledged Challenges, Questions & Unknowns
Non-uniformity makes bamboo pole construction much more difficult in application than working with other structural materials, such as timber and steel.
Resources
1 | NDT Resource Center: Mechanical Properties
2| Buckingham, Kathleen Carmel et al. “Can’t see the (bamboo) forest for the trees: examining bamboo’s fit within international forestry institutions.” Ambio vol. 43,6 (2014): 770-8. doi:10.1007/s13280-013-0466-7, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4165839/
3 | Yiping, Lou, et al. Bamboo and Climate Change Mitigation. International Network for Bamboo and Rattan (INBAR), 2010, Bamboo and Climate Change Mitigation. https://pdfs.semanticscholar.org/ade7/35f8da69384db2a6d21723621c1dbdd4a665.pdf.
4 | FactSheet, Forest Stewardship Council-US, “Family Forest Overview of the FSC-US Forest Management Standard.” January, 2011
5 | MOSO Sustainability from cradle to cradle
6 | Liese W (2009) Bamboo as carbon sink – fact or fiction? In: VIII world bamboo congress proceedings, Bangkok, Spet 2009. https://www.cabdirect.org/cabdirect/abstract/20103203149
7 | Stéphane Schröder, 2012 – Bamboo Preservation, Drying Bamboo Poles
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.678.7429&rep=rep1&type=pdf
8 | Raj, Ar. Dhenesh, and Ar. Bindu Agarwal. “Bamboo as a Building Material.” Journal of Civil Engineering and Environmental Technology, vol. 1, no. 3, 3 Aug. 2014, pp. 56–61., https://www.krishisanskriti.org/vol_image/03Jul201502074415.pdf
9 | Janssen, Jules J.A. Designing and Building with Bamboo. International Network for Bamboo and Rattan (INBAR), 2000, Designing and Building with Bamboo. https://www.humanitarianlibrary.org/sites/default/files/2014/02/INBAR_technical_report_no20.pdf
10 | Ann Knight, Resource Fiber – Why Bamboo?
11 | Syeda, Ayesha, and Barvaliya Shrujal Jayesh Kumar. “A Case Study on Bamboo as Green Building Material .” International Journal of Engineering and Advanced Technology, vol. 4, no. 2, Dec. 2014, pp. 78–82.
Additional Resources:
Building with Bamboo: Design and Technology of a Sustainable Architecture, Gernot Minke
Bamboo Architecture & Design (Architecture & Materials), 2014, Chris van Uffelen
Where Bamboo Grows: https://www.bamboogrove.com/where-bamboo-grows.html
Ogunbiyi, Moses A, et al. “Comparative Analysis Of The Tensile Strength Of Bamboo And Reinforcement Steel Bars As Structural Members in Building Construction.” International Journal of Scientific & Technology Research, vol. 4, no. 11, Nov. 2015, pp. 47–52., https://pdfs.semanticscholar.org/8ebc/a8a700fcde963fe96218e75265283234ee61.pdf.