Saturday 22 October 2011

Materials Choice

In February 2011 I saw an article in Owner Builder Magazine about hemp construction, but dismissed it as too new and untested. At that time I wanted an exposed post and beam timber frame and was looking at natural infill materials. I researched Light Straw Clay, but had concerns about the straw rotting before the walls dried and the time required for the walls to dry. Hemp lime masonry and light stray clay use different materials but in a similar way, combining a fibre together with a binding substance.

I began to research hemp lime masonry construction and found that while it is relatively new in Australia it has been used in the UK for over 10 years and in France for 20 years. First stop I read “Build a House of Hemp”. I found UK book “Hemp Lime Construction” by Rachel Bevan and Tom Woolley a great resource, scientifically looking at the pros and cons and data in relation to hemp lime building. Also useful was an early study in the UK on the Haverhill Project done by the Suffolk building society, comparing the construction and performance of a hemp masonry building as compared to standard UK masonry construction.  "The Green Self Build Book" a UK book by Jon Broome also has a section on the hemp masonry renovation and extension carried out by architect Ralph Carpenter.

If I was going to build with hemp masonry the exposed timber frame had to go, and this was probably good from a maintenance point of view. One of the benefits of hemp lime construction is that it completely covers the timber frame protecting it from termites and rot, the hemp lime being termite proof and the lime and breathability of the walls assisting in the rot resistance.

Weighing up all the factors hemp lime masonry came up as my first choice for walling, it combines insulating and thermal mass properties, it reduces gaps by being poured monolithically in place, reduces the double handling of mud bricks, it is lighter and would be easier to work with than mudbrick or rammed earth, the lime sets as it mineralises avoiding the problems of clay rewetting, it has a comparatively low embodied energy and primarily uses natural materials.

No comments:

Post a Comment