At last! Straw is being taken seriously once more as a construction material

What if we could rapidly grow large quantities of a high-performance, carbon-negative building material? As it happens, we already do.

With the accelerating need to move to a post-carbon economy, we’ve seen a resurgence of interest in bio-based building materials. Straw buildings first emerged in Nebraska in the late 1800s in parallel with the advent of the first baling machines. Some very early straw buildings from the turn of the last century still exist, which is a testament to the durability of the material.

Plants absorb carbon from the atmosphere via photosynthesis as they grow. This carbon then remains locked away within the fibrous cellulose of the material for the duration of its life. Unlike some bio-based materials such as timber, straw performs this carbon-capture and storage process rapidly over an annual crop cycle. Each tonne (or ~10 cubic meters) of straw construction will lock up approximately a tonne and a half of atmospheric carbon (CO2e) – similar to the carbon footprint of a London to New York return flight. A typical three-bed straw home may use around seven tonnes of straw.

At Studio Bark we’re already exploring the exciting potential of straw, with two new homes securing planning permission this year; both via Paragraph 84 of the NPPF (National Planning Policy Framework). Thatch House is a modest and sensitive contemporary thatched home in rural Dorset, built using thatched cassette construction. Meanwhile, Burford House comprises a new family home with several holiday lets in Lincolnshire.

Besides its climate mitigation benefits, straw construction offers several other advantages. As a natural material, it is safe and healthy to work with and does not give off VOCs and other hazardous pollutants. At the end of its useful life, straw can be composted leaving no toxic waste for future generations. From a building performance perspective, it has great thermal properties, with a typical bale wall achieving a U-value of 0.1 W/m2K. Moreover, straw can achieve good airtightness levels and vapour permeability without relying on plastic membranes and tapes.

Straw is largely a byproduct of arable agriculture (wheat, barley and oats) but a vanishingly small quantity is currently used for building. In the UK, straw is abundant and affordable, with over five million tonnes of straw harvested annually from wheat alone. Sustainability consultant John Bulter has shown that redirecting a nominal single-digit percentage of the available straw, to construction uses could free up close to 300,000 tonnes for building. This is enough to build approximately 40,000 homes per year, more than 10% of the government’s annual housing-delivery target (or around 20% of current delivery rates).

Straw construction comes in many forms, such as load-bearing bale construction, or lightweight timber frame with infill. More recently we have seen the emergence of modular straw panel and cassette systems, such as ModCell, Ecofab and Ecococoon, as well as a range of board and panel products including Copano and Durrapanel. These modular approaches offer all of the usual benefits attributed to off-site delivery, in terms of quality and timescales, in addition to the natural advantages of straw.

Straw has been used to construct a range of building types from self-built homes to large institutional buildings. Some pioneering examples include the Lilac co-housing scheme in Leeds by White Design and the Enterprise Centre by Archetype.

For those interested to learn more about straw construction, there is an expanding range of resources available. The School of Natural Building have produced some excellent technical guidance and training, while the YouTube channel of ACAN – the Architects Climate Action Network – is a treasure trove.

As the built environment faces an escalating imperative to transition, straw buildings present a compelling option for natural, bio-based building. Further work is needed to develop capacity and supply-chain structures to enable this material to achieve wider adoption. However, with its carbon-capturing properties, affordability, and versatility, straw is well-positioned to play a significant and expanding role in efforts to address the global housing and climate crises.