One of the principles that we attempt to keep to at Red Kite is to try to utilise natural materials where possible. What makes a material a natural material? The definition is that it is a "material that comes from plants, animals or rocks".
There are various reasons that we construct using natural materials.
If a product is natural, then it generally means that it hasnt had to go through the same amount of energy intensive processing as something that is a manmade. It also often means that it is locally available rather than having to come from a specialist factory. A good example of this is the sheeps wool insulation that we are using in our project at the rear of 212 Gloucester Road, that is created locally in south Wales using wool from welsh sheep.
Nico installing sheepswool between stud
Natural materials that we use often have the chareteristic of being able to 'breathe'. A strange phenomena! A breathable material is one that is hygroscopic, it allows moisture to travel through it. This has a few associated advantages, it means that any moisture that builds up in the structure is able to get out. This is can be a problem when using un-hydroscopic cement renders if they crack and let moisture in that then gets trapped.
It means that humidity build up caused by occupants of a building (showers, cooking pasta etc), is buffered and absorbed by the walls and does not form on the wall surface. This helps stop problems like build up of mould and bubbling wall paper, which means that it creates a healthy and long last space. On our project we have used breathable materials in our whole wall build up (see cross section below), lime render internally and externally, wood fibre board, sheeps wool insulation, panelvent racking board and wood wool boards. And using light earth for our internal walls (this is discussed more later)
The image below shows the breathable racking board (panelvent) being fitted to the timber studs, the sheeps wool insulation is still visible packed between some of the studs.
Externally the lime render is applied straight onto the wood fibre board (a breathable natural insulation board) with a wet on wet 2 coat render. A mesh is worked into the base coat to enhance the strength of the final render. Lime in its pure form is a natural material as it originates from lime stone (calcium carbonate) an abundant natural mineral.
The natural products that we use in our buildings help to sequester (lock away) carbon from the atmosphere, this means that the carbon is held in the buildings fabric for its lifetime. The construction industry is a hugely polluting industry, particularly with the lavish use of cement in concrete (see previous blog post on the concrete free foundations), so it is really important that alot of awareness is put into trying to be as low carbon dioxide as possible, There is an interesting paper (available at https://www.academia.edu/5439665/A_COMPARATIVE_STUDY_OF_BRICK_AND_STRAW_BALE_WALL_SYSTEMS_FROM_ENVIRONMENTAL_ECONOMICAL_AND_ENERGY_PERSPECTIVES) that compares the two walls (one brick and one straw bale) for a building from a economical, environmental and energy perspective. The global warming potential (essentially how much carbon dioxide is emitted into the atmosphere) of the two wall build ups is very interesting. The figure for the brick wall is 61.5 (kgCO2eq) and the figure for the straw wall is -50 (kgCO2eq), so the building is actually helping to reduce the affects of climate change rather than adding to it.
On the 212 Gloucester Road project we are using light earth to from our internal walls, this is a mixture of clay taken from the digging of the foundations and straw, so it is a carbon sequestering building technique. You can see a photo of the light earth in it formwork below.
Check out the facebook video of Nico showing the technique at: https://www.facebook.com/212strawhouse/videos/515928388581916/?pnref=story
Keep an eye on our blog for the next stage, putting the green roof on and the internal lime putty plaster.