29 Sep 2015

Can a house really be made out of straw?

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Forget everything that The Three Little Pigs fairytale taught you; straw bale construction is a natural and affordable self-build construction method.

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Self-builders considering to build a home made out of straw need not worry about it being blown down by the big bad wolf, in fact many straw bale houses in the USA have been inhabited for over 100 years with no reason as to why they won’t last another century. Here in the UK, straw bale construction gained popularity in the 1990s, appealing to the eco-conscious. Growth in general awareness of this method of construction has led to an increasing number of buildings of this type in the UK.

Straw bale is a flexible and eco-friendly material for home-building that can be used in two ways: either load-bearing or infill. With the load-bearing technique, straw bale is stacked to directly support structural elements, such as the roof, intermediate floors and joists. The framed technique uses a timber frame to support the structure and straw bale to fill the gaps within the frame.

Keen self-builders wanting to take a hands on approach to building their own home will benefit from the simple and straight-forward advantages of straw bale construction. With good instruction and on-site supervision, even those with no previous building experience can pick up the basics of wall construction very easily.

Eco-benefits

Constructing your own walls will inevitably be a slower process than if you hired a contractor to do it for you, but it will save you money by reducing labour costs. However, straw bale construction may not be as cheap as you might imagine. This is because you will need to employ experts to complete certain aspects of your home-build – such as construction drawings, carpentry, roofing, plumbing and electrics.

Straw has fantastic thermal insulation values – typically a U-value of around 0.13. Well designed and built straw bale homes can easily achieve level 6 of the Code for Sustainable Homes. This means that a straw bale home will require very little energy input once built, saving future spend on bills and easing concerns surrounding environmental burden.

Flexibility is another advantage of straw bale building. It is a malleable material that is easy to bend and shape into curved walls or to carve out shelves within the structure. This is especially useful if you decide to add an extra window as there is usually no need to support the rest of the wall as the wall plate carries most of the load of the floor above and the straw bales act together as an integral material because of how they are pinned.

It’s also worth noting that this construction method is not just for rural living. Straw bale walls provide excellent natural acoustic insulation, perfect for blocking out the noise of the city. In fact, the acoustic values are so efficient that straw bale has been used in UK sawmills to reduce the noise pollution from loud machinery.

Concerns and misconceptions

When considering this construction method, many self-builders have concerns surrounding fire and vermin risks. However, when straw bales are stacks with plaster either side, the density of the bales is such that there isn’t enough air inside the bales for them to burn. Straw bale walls have successfully passed fire tests and satisfy Building Regulations. In fact, plastered straw bale walls are so fire resistant that they are often used as fire protection between semi-detached houses. With regards to mice and rats, straw doesn’t contain any food that will attract vermin and has no greater risk than any other type of building. Once plastered, straw bale walls will have no gaps to entice furry friends and no cavities for them to live in.

Another concern might be the temperamental British weather. If a straw bale wall gets damp before being plastered, it can be problematic. If the top and bottom of a bale is covered and it is just the sides that get wet from rain, this usually presents no problem, as they will quickly dry out. However, if a bale gets wet from above and below right through to the center, then it will start to rot. If a bale already in place becomes sodden it should be disregarded, but is simple to replace. Any bales that are rained on or stand in water whilst in storage should also be disposed of.

Expert guidance

Barbara Jones – Director of leading authority on straw bale building, Straw Works – has created a practical manual for anyone keen to learn how to build with straw bales. 'Building with Straw Bales' covers everything from design principles and how to protect walls from the weather through to detailed analysis of how straw performs with humidity and how straw bale buildings can easily meet Building Regulation requirements. Straw Works also offer a number of training courses to help anyone preparing to build with straw bales.

Further information....

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