A little bit about Breathability and Humdity Control...

Many times I imagine most of you have heard the word 'Breathability' mentioned when refering to Lime or Clay based stucco's and plasters. Generally it is explained that this is a materials ability to allow vapour to pass freely through it, improving indoor air qaulity and protecting against mold growth, rot etc. This in essence is true, however, there is a little bit more to it than that. Anyway, as an aid to explaination I came across a paper written in 2005 by a chap called Neil May of NBT in the UK. Breathability; The key to building performance which points it out nicely.

" Breathability in buildings is not really about air1. It is about water: water as a gas and water as a liquid; water inside the building, water outside the building, and water in the walls, floors and roofs themselves (though not about water in pipes!)  It is not only about how water moves through structures (water vapour permeability), but also about the ability of materials to absorb and release water as vapour (hygroscopicity) and about the ability of materials to absorb and release water as liquid (capillarity). Water affects everything in building from the health or decay of building fabric, through to the thermal performance of the building and to the health of occupants. Particularly as we try to increase the airtightness, thermal performance and indoor air quality of our buildings, breathability has become a critical issue, affecting all areas both of new build and of renovation " .

I have also, as a show and tell, provided a simple little video that one of the manufacturers of a product we use, American Clay created a while back.This further demonstrates a component part of the term 'Breathability' namely Humdity control, and shows how these Clay Plasters can effect your indoor space.