Building Sustainable Walls.
Previously I wrote about green’ walls. We can now have a closer look at some options. For those of us following the green house-building path, the particular choice of what to use to build external walls can require some thought on how costs balance with thermal efficiency. Natural materials from renewable or recycled sources are the obvious first choice for an eco-building. A possible design solution for a home that sits lightly on the planet would maybe include a slate or timber shingle roof on lime or clay rendered straw bale walls, all sitting on shallow stone foundations.
Material Properties … An external wall need not be a cavity wall. We only need cavities where the materials are not very good at keeping out water or keeping in heat. The material must be structurally stable, should insulate thermally, be reasonably fire resistant and prevent moisture ingress. There are not many suitable natural materials for our climate which spring immediately to mind except perhaps logs however other materials can also be used if they are built and protected efficiently.
Straw Bale Walls … These have gained much support in recent years, even in our own damp climate. They have been built in Ireland since 1996 and in the UK since 1994 and it is feasible to build two-storey load-bearing walls. Straw bale homes can potentially last for over 100 years, the bales lock up around 12 tonnes of CO2 in an average 3-bedroom house, they provide a low ‘U’ value of about 0.13 and are sourced from cheap excess agricultural produce. Not much wrong there then.
The key to success with the technique of course is good design and workmanship. There are a number of ways to build these walls but most nowadays will use some sort of framework (usually timber), make use of roof overhangs to protect the external face of the walls and will sit above ground level to avoid soaking up moisture. Natural renders will create warm, softly curved walls and will also provide an element of fire protection and deter the little critturs which might like to burrow in and create nests. (Compressed bales will minimise both of the above risks.)
Eco-Extensions … External and internal straw bale walls can be built to extend your home too. Some factors need to be considered, such as differential settlement between the different structures and the thickness of the walls but these can be easily sorted out at the design stage. In the US, there are straw bale houses which are reckoned to have been standing for about 130 years. Have a look at these websites:
http://www.strawbale.com (Excellent website with good information)
http://www.amazonails.org.uk (Experienced straw bale builders)
http://www.strawbale-building.co.uk (Good image gallery – UK and Ireland)
Related posts:
- Green walls
- Surface Finishes Part 4 – Wall coverings
- Health and eco homes
- Eco Friendly Plaster
- Compost Trouble Shooting
