FUTURE of STRAW-BALE HOUSING in India.

Nayan Das highlights the potential of straw-bale as an energy-efficient construction material and how it can improve the current scenario of the housing market in India.

India's population is growing at an average rate of 1.02% annually.¹On the surface, it may seem like a small increase. However, considering our current situation, we should be aiming to reduce it. The population explosion has caused two serious problems (amongst others) in the Indian socio-economic system. Firstly, it has put a huge pressure on the housing market to constantly meet the demands of producing livable dwellings for the Indian citizens. The second problem is not tangible. But it influences the social dynamics of our communities. The ongoing increase in population has drastically affected the well-being of Indian families who do not have a sufficient individualized space to live a dignified life. Available statistics from the Census of India indicate that more than 20% of Indian married couples have to share their room with another couple/family.² Although the problem of sharing the same room between two couples cannot be quantified in terms of noticeable profit and loss, it has an enormous impact on the mental health of Indian families. While there has been inspiring initiatives from organizations such as Griha Council and Bamboo House India to promote affordable housing and use of sustainable materials in residential homes, there is a completely unrecognized market for straw-bale which can certainly be utilized in building low-cost houses in India.

Straw-bale: Material and its properties

Straw-bale is a residue of crops such as rice and wheat which are left standing in the agricultural fields after a harvesting season. As a general practice, Indian farmers burn-off the residual crops to clear the field for the next season. In doing so, we are not only suffering the loss of prospective building material but also witnessing emission of carbon dioxide and methane into the environment as a result of the burning.³On the contrary, a green approach would be to utilize the hidden properties of straw-bale and produce it commercially for the construction industry. India is the second-largest producer of rice in the world. In order to take advantage of producing more than the average rice crops as compared to other countries, we should be starting to promote straw-bale as a sustainable building material.

Straw-bale is a renewable material with low embodied energy, high tensile strength and excellent insulation properties. It has been used as a wall material for more than a century in countries like the USA, France, UK and Australia.^4,5 However, when it comes to India, it is not even recognized as one of the predominant wall materials. Figure 2 provides the percentage distribution of the top five-wall materials in India taking into consideration rural and urban households respectively.

For a building material or wall material to be affordable and energy-efficient, it should be able to fulfil certain essential criteria. One of the requirements is the local availability of the material. Another critical condition is the low-labour cost for handling and storing the material. However, the most important prerequisite is the sustainability of the material. This involves durability, human comfort and environmental impacts of the material. Straw-bale has the promising ability to meet all these requirements and become the future green material for our low-cost houses.

Rice straw contains a high amount of silica making it dense and resistant to decomposition. A well-engineered straw-bale wall can last for about 100 years. Following are some of its properties that will inspire construction practitioners to support its application in building affordable houses:⁶

• Thermal Insulation: It provides superior thermal insulation during cold nights and hot days. An R-value of greater than 10 can easily be achieved by an average straw-bale wall. As a result, it reduces the overall heating/cooling costs and makes the house energy efficient.
• Sound Insulation: It enhances the acoustic performance of the building. The dense straw-bale wall improves the wellbeing of the habitants inside the house by maintaining a quiet environment for calm living.
• Fire Resistance: Fire needs air to thrive. A densely packed straw-bale wall mimics an airless setting and consequently, its fire resistance is exceptionally good.

How to build a straw-bale wall?

Any woman and man can master the art of building a straw-bale wall with little instruction on site. As a minimum requirement, the construction will need straw-bale, clay-based plaster and lime plaster. Traditionally, local men and women gather around the site and perform 'bale-raising'. This is similar to a fund-raising event where people gather together to accumulate and compact straw-bales instead of raising money for a cause. In general, bales are compacted to form a cuboidal unit of approximately 900mm x 450mm x 350mm.

Once the dried bales are compacted, one can begin the construction of the wall in the same fashion as one would do for any brick wall. The bale units are laid next to each other in a 'running bond' and aligned vertically using a tensioning wire at 450mm centre to centre. Tensioning wires can be a conventional fencing wire of about 2.5mm thickness. Figure 4 provides a reference to a typical straw-bale wall. Unlike cement and lime which are aggressive to our skin, clay-based plaster of about 40mm can be used to render the inside part of the wall. The idea is to fill the gap between the bales with clay to provide a seamless aesthetic appearance. Unfortunately, clay-plaster is not suitable for exteriors. It cannot withstand rain and snow. So, it is recommended to coat the external face of the wall with a tough lime-based plaster.⁹

It is important to highlight that new construction methodologies are available in the market which provides guidance for building both load bearing and non-load bearing structures using straw-bale. Bamboo and wood can also be used as a reinforcing material to withstand greater loads when building two or more storey houses. It is generally advised to have a minimum wall thickness of around 350 mm and to limit the maximum height of a straw-bale wall to 2.5 metres.⁶Qualified professionals, architects and designers should be consulted for appropriate structural design and drawings prior to starting the construction at the site.

Conclusion

Nature binds all aspects of life. Straw-bale promises to become the new sustainable material in the Indian market alongside bamboo, engineered wood and rammed earthen materials. It is energy-efficient, durable, fire resistant and can be easily repaired in the event of damage. Like any material, it also has few limitations. It is susceptible to wet environment and moisture attacks and hence, bales are required to be kept away from rain and in an environment with moisture content less than15% by weight. It is also bulky and hence, it takes up more space than ordinary brick or aerated concrete blocks. In addition, there can be often no cellular network inside a straw-bale house due to the dense compaction of the bales. We may perceive this as a negative feature, however, occasionally it is good for personal as well as family well-being to switch-off the digital world in order to rejuvenate ourselves. In a nutshell, the benefits of straw-bale far outweigh the risks making it the future material for resilient habitats in India.

References:

1. The World Bank Group, 2020. Population growth (annual %) – India. Details available at: https://data.worldbank.org/indicator/SP.POP.GROW?end=2019&locations=IN&start=2019&view=bar; last accessed on October3, 2020.
2. Office of the Registrar General & Census Commissioner, India, 2011. Houselisting and Housing Census Data – 2011. Details available at: https://censusindia.gov.in/2011census/Hlo-series/hlo.html; last accessed on October5, 2020.
3. Ravindra Kumar et al., 2016. “Life cycle assessment of rice straw utilization practices in India.” Journal details available at: https://www.sciencedirect.com/science/article/abs/pii/S0960852416317606; last accessed on October5, 2020.
4. European Straw Building Association (ESBA), 2016.ESBA – European Straw Bale Gatherings. Details available at: http://www.strawbuilding.eu/category/parent/research/; last accessed on October6, 2020.
5. Australasian Straw Bale Building Association, 2020. Straw Bale Building in Australia, New Zealand and the rest of the World. Details available at https://ausbale.org/resources/a-brief-history; last accessed on October6, 2020.
6. (PaulDownton)Department of the Environment and Energy, 2017. Your Home: Australia's guide to environmentally sustainable homes, 5th edition. Details available at: https://www.yourhome.gov.au/materials/straw-bale; last accessed on October6, 2020.
7. Strine Environments, 2013. Concrete and Embodied Energy – Can using concrete be carbon neutral. Details available at: https://strineenvironments.com.au/factsheet-concrete-for-carbon-neutral-housing/; last accessed on October7, 2020.
8. Paul Downton, 2012. Straw bale: An enduring building technique. Details available at: https://renew.org.au/sanctuary-magazine/building-materials/straw-bale-an-enduring-building-technique/#:~:text=When%20building%20with%20straw%20bale,of%20just%20over%20500%20millimetres; last accessed on October7, 2020.
9. Dw TV – Eco India, 2019. House made of straw bales. Details available at: https://www.dw.com/en/house-made-of-straw-bales/av-47612050; last accessed on October8, 2020.
10. Melanie Pearce, 2016. Latest technology in straw bale home construction comes to Canowindra organic farming community. Details available at: https://www.abc.net.au/news/2016-01-11/new-straw-bale-home-latest-for-unique-organic-farming-community/7080612; last accessed on October8, 2020.

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