Why we build with agricultural residues

The construction sector is responsible for 39% of global greenhouse gas emissions (King and Magwood, 2022). A growing number of practices respond to this by specifying timber. The logic is straightforward: trees absorb carbon, wood stores it in the building, and the forest regrows. We think the logic has a timing problem.

Softwood forests take 45 to 180 years to regrow after harvest (Pittau et al., 2018), and plantation softwoods 20-30 years. Rice and wheat straw regrows in a single season. When Pittau modelled five wall systems using dynamic life cycle assessment, the timber frame option took 79 to 101 years to reach negative net radiative forcing - that is, to actually reduce the energy imbalance in the atmosphere that's causing global warming. The straw wall made an impact almost immediately. The straw wall got there almost immediately. A 2025 Munich case study on a school retrofit measured the difference directly: over a 50-year building life, straw insulation delivered 13.5 times the climate relief of wood-fibre insulation from an 80-year rotation forest (Santamaría-Herrera, Otaegi and Rodríguez-Vidal, 2025). Even cutting the rotation to 60 years, straw was still nearly fivefold ahead.

Standard LCA methods hide this. The static approaches used in most EPDs weight all emissions equally regardless of when they occur. Hoxha et al. (2020) found errors of 35 to 200 percent at component level between static and dynamic methods. Every static comparison of straw against timber is structurally biased toward timber, because it erases the one variable that matters on a 2050 timeline: how fast the feedstock recaptures its carbon.

The supply question compounds the problem. Mishra et al. (2022) modelled housing 90% of new urban population in engineered timber and found plantation forests would need to expand by up to 149 million hectares by 2100, with increased harvest pressure on unprotected natural forest. The world has already lost a third of its forests, half of that in the last century alone (Ritchie and Roser, 2021). FAO's 2025 assessment still records net forest loss of 4.12 million hectares per year (FAO, 2025). Scaling demand against a shrinking stock is a strange climate strategy.

Agricultural residues need no land at all. They are a co-product of food we already grow. Pittau et al. (2021) compared timber, straw, hemp and cork across Europe and found straw ahead on both resource availability and carbon storage potential. Hansen et al. (2024) showed that substituting fast-growing biobased materials into Danish timber buildings cut wooded-land requirements by 50 to 61 percent.

In Indonesia, where we do much of our work, the residue stream is large and most of it is on fire. Andini et al. (2018) put Indonesian open burning at 45 million tonnes of crop residue per year, about 21% of national residue production. Rice straw accounts for 19.3 million tonnes. That burning releases roughly 49,671 Gg of CO₂ annually, plus black carbon and fine particulate pollution that the WHO (2024) links to 4.2 million premature deaths worldwide from ambient air pollution, with the heaviest burden in South-East Asia. Indonesia alone accounts for 12 to 14% of global warming potential from crop residue burning (FAO, 2024).

This changes the carbon accounting in kind. Timber gives you one effect: substitution of concrete and steel. Residue gives you three. You avoid an emission that is definitely happening. You store the carbon. And you displace conventional materials. The counterfactual for timber is a standing tree. The counterfactual for rice straw is a fire.

The performance is there. Straw-based EPDs report global warming potential of -101.2 to -146.5 kg CO₂-eq/m³ cradle-to-gate, with thermal conductivity of 0.043 to 0.068 W/mK (Santamaría-Herrera, Otaegi and Rodríguez-Vidal, 2025). Each kilogram of straw holds about 1.35 kg CO₂. Straw is an envelope and insulation material, not a long-span structural one. We are not arguing against timber where fibre length and tension capacity are irreducible. We are arguing that for every square metre of wall, ceiling and insulation (the bulk of material volume in any building) residues do more climate work, faster, with fewer ecological costs.

Two honest concessions. You cannot take all the straw. Soil needs some returned. But the numbers favour building: straw incorporated into soil retains about 50 kg of carbon per tonne, while straw in the building stock retains 240 kg per tonne (Pittau et al., 2019). And EN 15804, the standard governing EPDs, forces biogenic carbon to be re-emitted in end-of-life modules C3-C4, which means every compliant straw EPD understates its own storage (Ortech Industries, 2020).

We use compressed strawboard, bamboo and lime. The rice straw we specify in Bali and Lombok would otherwise be burned in a field. Every panel we install is a small piece of pollution that did not happen, locked into a wall for decades, displacing concrete block. That is what regenerative architecture looks like when you follow the carbon rather than the convention.

References

Andini, A., Bonnet, S., Rousset, P. and Hasanudin, U. (2018) 'Impact of open burning of crop residues on air pollution and climate change in Indonesia', Current Science, 115(12), pp. 2259-2266.

Food and Agriculture Organization of the United Nations (2024) FAOSTAT: Burning - Crop Residues. Available at: https://www.fao.org/faostat/en/#data/GB (Accessed: 30 August 2026).

Food and Agriculture Organization of the United Nations (2025) Global Forest Resources Assessment 2025. Rome: FAO.

Hansen, R.N., Hoxha, E., Birgisdóttir, H. and Pittau, F. (2024) 'Reducing the land-use impact of wooden buildings with fast-growing biobased materials: A Danish case study', Resources, Conservation and Recycling, 209, 107776.

Hoxha, E., Passer, A., Saade, M.R.M., Trigaux, D., Shuttleworth, A., Pittau, F., Allacker, K. and Habert, G. (2020) 'Biogenic carbon in buildings: a critical overview of LCA methods', Buildings and Cities, 1(1), pp. 504-524.

King, B. and Magwood, C. (2022) Build Beyond Zero: New Ideas for Carbon-Smart Architecture. Washington, DC: Island Press.

Mishra, A., Humpenöder, F., Churkina, G., Reyer, C.P.O., Beier, F., Bodirsky, B.L., Schellnhuber, H.J., Lotze-Campen, H. and Popp, A. (2022) 'Land use change and carbon emissions of a transformation to timber cities', Nature Communications, 13, 4889.

Ortech Industries (2020) Environmental Product Declaration: Durra Panel. EPD Australasia, S-P-10940.

Pittau, F., Krause, F., Lumia, G. and Habert, G. (2018) 'Fast-growing bio-based materials as an opportunity for storing carbon in exterior walls', Building and Environment, 129, pp. 117-129.

Pittau, F., Lumia, G., Heeren, N., Iannaccone, G. and Habert, G. (2019) 'Retrofit as a carbon sink: the carbon storage potentials of the EU housing stock', Journal of Cleaner Production, 214, pp. 365-376.

Göswein, V., Reichmann, J., Habert, G. and Pittau, F. (2021) 'Land availability in Europe for a radical shift toward bio-based construction', Sustainable Cities and Society, 70, 102929.

Ritchie, H. and Roser, M. (2021) 'The world has lost one-third of its forests, but an end to deforestation is possible', Our World in Data. Available at: https://ourworldindata.org/world-lost-one-third-forests (Accessed: 30 August 2026).

Santamaría-Herrera, N.M., Otaegi, J. and Rodríguez-Vidal, I. (2025) 'A review of recent advances in the application of cereal straw for decarbonization of construction materials and applications', Sustainability, 18(1), 65.

World Health Organization (2024) Ambient (outdoor) air pollution, Fact sheets. Available at: https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health (Accessed: 30 August 2026).