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| Left, The roof plate stuffed with straw after the side panel has been removed. As this is in a 18mm wooden box, this straw doesn't need to be dipped in clay slip. | ||
Straw loose-fill insulation
JOIN THE INSULATION REVOLUTION (MUD BATH)
We will be insulating the roof of the building using straw (tentative date is 24th and 25th February 2007). This event will be open for volunteers and anyone who wants to learn these unusual building techniques by experience.
Why is insulation so expensive when everybody needs it? It should be incredibly cheap. It isn't, especially if you want something that isn't a petrochemical product or horrible to handle. Wool, for example is £8 per square metre. I have 65 of those in my roof. If I used no insulation at all it would still take me years to burn £520's worth of energy. So, what can I use as an alternative that is really cheap and a really good insulator.
Um, straw?
been soaked in a clay slip.
Used as a loose fill, straw apparently has a similar U value to Warmcel, which would cost £460 for 8 inches of insulation. I paid £3 a bale and I doubt it will take 153 bales. I have bought a load of second hand ply to create a layer above and below so that the loose fill is boxed in. It is important that there is an air gap above the insualtion to prevent condensation, so the top layer of ply is perforated with holes. |
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Because commercial loose-fil insulation is fire-proofed we will be dipping the straw in a clay slip before stuffing it. This really does work as fire proofing and it also means the straw solidifies when it dries. I'm using clay from the site, of which I have an infinite supply. The process is quite messy, but in a mud-pies fun kind of way. Besides, clay is very good for the skin. |
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Peter Beresford, the structural engineer, suggested I find out how much the clay slip will add to the weight of the straw, which, of course, is a light material. Here are the results of a simple test. I think I will repeat this test again, just to be scientific, but for the moment it is a reasonable guide to the relative weights of the materials.
Weight of straw = 145g
Weight of straw when soaked in slip = 690g
Weight of slip-dipped straw when dry = 320g
The weight is approximately 5 times the original weight of the straw when wet, i.e. during installation.
Once dried the final weight is approximately double the original weight of the straw.
Volunteering details:
Cost: Free
Date: Saturday 3rd March 2007
What you need to bring:
I will supply rubber gloves and those fashionable all in one overall things. You'll need stout boots, because it is a building site. As usual we will provide lunch.