Strawbales uniquely combine very high insulation values with very light weight, low cost, environmental footprint to produce and transport (if locally sourced), structural stability and durability, resilience and fireworthiness. Efficient use of resources (economically and environmentally) requires building materials to serve several functions at once, and strawbale construction shows excellent multi-functional qualities in this way. Conductivity values (a measure of how much heat escapes every second) are typically 0.05 W/m.K, while common insulation materials like polyurethane foam or glass wool are around 0.03 or 0.04. Brick or cement is 20 times worse, at around 1.00 W/m.K. A strawbale wall with lime or clay plaster would typically cost 1/5 of a masonry wall with foam insulation (as typically built today), and pass about half the amount of heat energy.
Natural building methods typically use natural materials (like earth, wood, straw) which are readily available locally, with minimum industrial processing and transportation, and a minimum of expensive and energy-consuming machinery and plant for constructing the buildings. All processes are carried out with sensitive consideration of their impacts on local environments and communities. So because they involve very low use of energy (whose generation emits greenhouse gases and other pollutants), and low disruption or adverse effects on local surroundings, and because they use renewable and locally abundant resources, and are also readily re-used or recycled (again with little adverse impacts), their overall ‘environmental footprint’ is very favourable. Making high use of local manpower and craft skills (rather than mechanical automation and technical specialists sourced from far afield) also reduces travel and social disruption impacts.
Constructing and using buildings is responsible for around one third of UK’s current carbon emissions, so if we are serious about keeping global warming within 1.5 or 2°C then buildings must be designed to much higher energy standards – such as UK’s Code for Sustainable Homes level 6 or Germany’s Passivhaus rating. However in 2015 the government abolished the statutory requirement to build to these energy standards.
Current new builds tend to involve a higher amount of factory prefabrication, largely aiming to reduce costs and construction times – although the higher precision of construction and optimised material use can also improve heat loss performance. Designs often do pay greater attention to heat loss, minimising this by adding more foam or fibre insulation to masonry walls or else using prefabricated timber frameworks and (in principle) minimising draughts and air leaks. Masonry and industrial insulation products both use large amounts of energy to produce, so this ’embodied energy’ in construction is still not well addressed – but wood frame construction can have a better environmental footprint if the timber is responsibly sourced. So the general UK picture is of more optimised industrial technology giving some improvements in sustainability for new builds – but very little is being done to address the much greater issue of energy performance in UK’s ‘legacy stock’ of buildings already constructed. A small minority of construction, however uses ‘natural building’ methods, which take a very different approach to provide good sustainability in both construction and long-term use.