The oldest straw bale houses are around 130 years old, the oldest European house in France dates back to 1921. When a brick dated to 3000 years old was broken apart the straw inside was as bright and golden as the day it went in. But is this a form of construction we can still use today – and in Orkney?
In this series of columns I will touch on the history of straw construction, Tools and Skills, Planning, Building Warrant, Site, costs, Environment, and at least obliquely other green building systems.
“No Straw Bale house has ever been refused Planning merely because it was Straw bale”
Our Orphir house went straight through with no problem. What is more Straw bale houses have come of age as the first Council House tenants are now in residence in their Straw bale houses and are reported to be delighted. With “fuel poverty” becoming more prevalent I can see more Councils building their stock this way.
Apart from needing a Structural Engineer’s report there are no unusual problems here. Even less so now as OIC Building Standards has a good handle on Straw bale construction.
As with all structures it needs to be well drained. Lack of adequate drainage was one of our problems. Ideally you will need to follow standard Orcadian practise and point the smallest side into the wind.
Because of the significantly lower weight the foundations do not need to be as deep nor do they need concrete. The Orphir house foundations are compacted crushed rock.
Rendering and Plastering
Clay, if you have, it is beautiful. I have never worked with such a forgiving material before or since. It is ideal for the beginner since if you decide that it’s a complete mess that you can’t live with,just scrape it off remix it and reapply.
Here in Orkney I would not recommend clay for an external render unless it was an unusually sheltered site. In sheltered locations there are clay structures known to be over a 1000 years old and there are Cob houses in the southern counties which are 700 years old. The old saying about Cob houses equally applies to Straw structures:
“They need a good pair of shoes, a good hat and overcoat”
Failing clay, then it MUST be Lime. NEVER EVER USE CEMENT.
Lime renders and plasters breathe – cement doesn’t. So when you get water coming in through leaks or micro cracks in a cement render the water stays there. Lime is also easier to use and much easier to repair. It’s more expensive than cement but not as much as you might think since wastage can be much lower. Lime mortars, renders and plasters can be kept in usable condition for 2 months or more.
The aggregate for these renders and plasters needs to be selected with care. Beach sand can only be used for internal finish plaster coat after it has been very well washed to get the salt out. Failure to wash it will encourage damp.
Damp is a vicious enemy of straw! I have had very good results using Orkney Aggregates “dust”. The clay content works well with lime, unlike cement.
In Part 3 I will consider the ecological advantages to Orkney and the planet with straw bale construction.
More information on Straw bale construction here Straw Works