Straw has been used as a building material for centuries. Many people worry a house made of straw may be flimsy or weak structurally. In fact the opposite is true, straw walls look and feel incredibly strong and comforting. Structurally it is able to support a two storey building, however used as infill on a
Straw has been used as a building material for centuries. Many people worry a house made of straw may be flimsy or weak structurally. In fact the opposite is true, straw walls look and feel incredibly strong and comforting. Structurally it is able to support a two storey building, however used as infill on a timber frame this can easily be increased if necessary.
Another huge concern is fire. Straw itself is burns easily and quickly, so you may not think of it as an ideal material to use in your home. However the straw bales when tightly compressed provide a good level of fire resistance. The walls will also be plastered, which will provide an extra level of resistance.
Advantages of Straw Bale Construction
The UK produces approximately 2 million tonnes of surplus straw each year, which only adds to its eco credentials as a building material. It is very low in embodied energy and has a negative carbon footprint. It also achieves insulation values far lower than those required by the Building Regulations. Currently walls a required to have a maximum U (insulation) value of 0.27wm²K. A 450mm straw bale wall will achieve 0.13wm²K. So not only does the material take little energy to produce you also need less energy to heat/cool the building in use.
Perhaps the most compelling argument for using straw as a building material is the cost. Labour costs are reduced as skilled tradesmen are not required. In fact anybody could learn to build with straw in just a few hours (provided you are able to lift the heavy bales. The cost of the wall construction can be less than half that of traditional construction.
Disadvantages of Straw Bale Construction
The big drawback with straw is water. This isn’t a problem once built as the straw will be protected by plaster and the roof. However during construction the straw will need to be protected from the elements. This can involve large dry storage areas on site and tarpaulins on stand-by ready for the inevitable British rain.
Designing the house so the roof can be built first can help alleviate these problems. The roof should have a substantial overhang to prevent water running down the walls. This overhang can also provide protection for the walls during construction. Another issue can be the thickness of the walls. Bales vary in size between 450mm and 600mm deep. Compare this will a typical cavity wall of around 300mm. While the thickness may not seem a lot it will take up additional space which could cause problems on smaller sites.
Would I Get Permission To Build?
The construction materials and techniques are not considered at the planning stage. Planning Permission largely deals with the appearance, location and scale of the building. The building will need to meet the Building Regulations, however if detailed correctly this shouldn’t cause too much difficulty.
The straw bales can be the main structural element of the walls, or the walls could be built using a frame with the straw as an infill material.
Structural Straw Bale Wall
This is the simplest method of straw bale construction, suitable for buildings up to two storeys. The straw bales are simply stacked on top of the ground floor slab. They can either be “staked” together using timber or stainless steel pegs, or fixed using eye bolts and strapping.
Timber Frame with Straw Bale Infill
This method has several advantages. Firstly you can build as higher as the timber adds strength to the construction. All structural components are built first including the frame, floors and roof. This means you can have a dry area to store bales and they will also be protected from the weather during construction. Once the structure is complete the bales can be installed between the frame members.