Straw Bale Buildings - Do They Represent an Increased Exposure?
Houses made of straw have been offered for sale on the open market in the UK for the first time.1 Using a timber framework with wooden board walls that are insulated with straw bales, the buildings are the result of an engineering research project led by the University of Bath (UK) and the specialist architectural firm ModCell.
The selling points for these buildings claim that they are CO2 neutral and have outstanding thermal insulation that will reduce energy consumption by up to 90% compared with conventional dwellings. Furthermore, straw is a low-cost material, widely available as a by-product of food production.2
On the downside, straw is combustible, easily ignitable and not water resistant, meaning that additional fire, water and general weather resistance measures need to be implemented.
Interestingly, straw bales are classified as a normal combustible material in Germany, according to the DIN 4102 standard, alongside building products made of wood. Research recently undertaken in Germany compared straw bale insulated constructions with ordinary wood-framed structures and produced some useful results.3
The research found that straw insulated buildings can attain a fire safety level equal to a fire resistance of 60 minutes, so long as the straw bale insulated walls are cladded with a fire retardant chalk/clay-plaster.
However, as a caveat, the researchers noted that the long-term durability and resilience of such plaster has not yet been established, stating that it is important that the plaster is regularly checked to ensure the cladding of the straw bales is undamaged and fire cannot spread through any cracks or openings.
Overall, the researchers concluded, straw insulation still represents a higher fire risk, which needs to be mitigated by installing a fire and smoke detection system throughout the entire construction.
Chalk/clay-plaster cladding might sound all very well and good, but it could pose problems for insurers as it makes it a challenge for surveyors and underwriters to identify straw bale constructions, potentially leading to misjudgments in underwriting.
Of course, the UK doesn’t have a monopoly on new, sustainable construction materials and it’s likely that green buildings will soon be a feature of insurers’ homeowners portfolios right across Europe and North America. In that sense, the sector represents a genuine growth opportunity for insurance companies that are prepared to offer the cover.
But, insurers of straw-built houses will also be exposing themselves to a potentially higher frequency and severity of losses from fires and “wet” perils. That’s why we believe that understanding the exposure posed by these buildings, and making sure the proper fire, water and weather-related protection measures are in place, will all be essential to underwriting the exposure in the future.
For more information about straw bale construction, get in touch with your local Gen Re property facultative underwriter.
1. "First straw homes go on sale", The Guardian UK, 9 Feb 2015.
2. "Green Building Constructions – Implications and thoughts on insurance issues", Gen Re, Insurance Issues, 19 May 2013.
3. "Neue Forschungsergebnisse zum Brandschutz für mehrgeschossige Strohballenbauten", vfdb Zeitschrift für Forschung, Technik und management im Brandschutz, Heft 1/2015, page 22 to 28.