New build:straw bale
From Sustainable Building Resource
[edit] Straw Bale Building
Top Tips:
Experiences
Home Grown Home [1] in Yorkshire have a great website that details their build and the issues around it.
Amazon Nails[2] have provided some FAQs for strawbale building. They are as follows:
What sizes do straw bales come in and what size walls do they make?
Standard size of straw bales (S/B):
450mm wide x 360mm high x 1-1.5m long (but occasionally different due to machines)
Average thickness of S/B walls: approx 500mm wide. Straw can be used as a party wall and is ideal for internal walls were sound insulation is necessary.
Smallest square S/B possible: about 3m x 3m Largest S/B possible: no limit – depends on design.
Rough cost of bales:
Direct from field – 1.50 each (collect yourself) Or £2.50-4.50 + dep on where and how far. (cost = diesel to move it)
Where can you get bales?
Straw wholesalers, agricultural merchants
Any questions about Lime:
Building Limes Forum: info@buildinglimesforum.org.uk
Glasite Meeting House,
33 Barony Street,
Edinburgh,
EH3 6NX
www.buildinglimesforum.org.uk
What is Cob Building?
Indigenous to the UK, building entirely from clayey earth, sand aggregate and straw. Usually made from sub-soil on which the house has been built.
Types of Strawbale building:
Loadbearing: Straw walls take weight without the need for a frame.
Infill: Framework of timber, steel or concrete, straw is used an insulation block by filling the gaps.
Compressive: Similar to loadbearing, but has a framework, and roof is lowered onto straw to compress and stabilise it.
What are the healthy alternatives to concrete?
Limecrete – hydraulic lime plus aggregate such as sand, gravel, blown glass or leca (blown clay). Glass & leca are also insulants.
How much will it cost to build my house/shed/animal sanctuary?
Regarding costings for your build-we recommend a price of approximately £1000/m2, which would include pricing for contract building the structure.
This estimate obviously varies greatly depending on the materials used, the design, and the method used to build: savings can be made by not paying for labour-either through building yourselves, or by us running courses with paying participants-and by using recycled materials.
Where are S/B buildings that people can go and look at?
National Trust Footprint Project Strawbale classroom – Cumbria
015394 88409
footprint@nationaltrust.org.uk
[3] (search for ‘footprint’)
Hackney City Farm Educational Resource Centre-Hackney, London
Shelf Library & Village Hall
Near Halifax, West Yorkshire
Westport Lakes Visitor Centre, Stoke
Ecology Building Society, Silsden, Nr Keighley, West Yorkshire
Clow Beck – Darlington, North Yorkshire
01325 721778 or info@clowbeckecocentre.co.uk
Agbrigg Community Allotment building – Wakefield
[7]
St Dogmaels – 2 storey loadbearing quietearth@ukonline.co.uk
Yarner trust – Devon
[8]
What about mice and rats?
There is no greater risk of encouraging mice and rats into your straw bale house than there is for any other type of building. Straw is the empty stem of a baled grain crop and unlike hay, it doesn't contain food to attract furry creatures. Any home where food is left out in the open is a potential lure for vermin. Once your strawbale house is plastered, the walls seem no different to a mouse than other plastered walls. Mice and rats like to live in spaces between things, as they are very sociable animals. In barns, they live in the gaps between bales and in houses they live in cavities and under floors. If you build straw walls and then clad them in timber, with an air gap between, this might attract mice: but it's the gap they like, not particularly the straw. If you build straw walls, plaster them with clay/lime and maintain them, then there are no gaps to invite them in, and no cavities in which they can live.
How long will it last?
No one can completely answer this question because the first straw bale house was built only about 130 years ago. In the USA there are about a dozen houses nearing 100 years old that are still inhabited and showing no problems. They have an increasing stock of houses built since 1980 that are also surviving with no problems. Here in the UK, we started building in 1994, and in 1996 in Ireland. As with any other technique of house building, if your straw bale house is built with a good design, with quality work and is properly maintained throughout its life, there is no reason why it should not last at least 100 years.
Isn't it a fire risk?
No, it may seem strange, but when you stack bales up in a wall and plaster them either side, the density of the bales is such that there isn't enough air inside the bales for them to burn. It's like trying to burn a telephone directory - loose pages will burn easily, but the whole book won't catch fire. Straw bale walls have passed all the fire tests they have been subjected to in the USA and Canada. See http://www.thelaststraw.org/resources/rg06/code.html for research, data and testing. Despite the bales themselves not being a risk, if you plaster any wall with a half inch of plaster, it gives sufficient fire protection to satisfy building regulations.
Is it really cheap to build?
It depends entirely on your approach to building. If you can put lots of time into collection recycled materials, or doing the drawings yourself and keep the design simple, or organise training workshops to build the walls and plaster them, or get your friends and family to help, then yes, it can be cheap to build. For most people, it is more sensible to think of doing the simple bits yourself (design, foundation, straw and plaster), and employing others to do the rest (carpentry, roofing, plumbing and electrics).
Can I do it myself?
Yes, parts of it are quite easy to build. Other parts like roofing and carpentry are more difficult. It depends on how much time, determination and dedication you have. But the straw building technique is simple, straightforward and accessible to almost everyone.
What about temporary buildings?
Design of straw bale buildings is very versatile, and can be adapted for a more or less durable function. If a building is only required for a few years, then there may be no need to build elaborate foundations, or plaster it inside or even outside.
What else can be built with straw?
Straw has been put to many uses. Apart from houses, studios, offices and community spaces, straw is also used for schools, warehouses, barns and stables, sounds studios, meditation centres, acoustic barriers for airports and motorways, food storage and farm buildings. (See www.sworder.co.uk for the largest strawbale building in the UK)
What if some of my bales get wet?
It depends on where, and how badly. Generally, if a bale gets wet through the top or bottom into the centre, then it will not dry out before it starts rotting. Any bales that are rained on, or stand in water whilst in storage, should be discarded. This also applies to any bales already in the walls that are not covered against the rain. But if you have covered the tops of the bales, and the sides get wet from the rain, this usually presents no problem, as they will quickly dry out once the rain stops. The only time this may not be the case is if the walls are exposed to severe wind and rain at the same time for prolonged periods, as the wind may drive the rain into the bale, where it cannot dry until the rain stops.
Is it possible to repair straw walls?
It is not only possible, it's very easy! The hardest part is making a hole through the straw. This can be done with a claw on a hammer or crowbar, and by just pulling at the straw. It can be quite difficult to make the first hole due to the density of the bale. However, once this is done, wedges of the bales can be pulled out quite easily. Hazel pins can be cut through if necessary, and fresh straw wedges can be packed tightly back to fill the gap. Experience has shown that if a section of the wall does get wet, damp remains remarkably localised. It tends not to spread further through the straw, and so wedges or flakes of the bale can be removed and replaced.
What if I want an extra window?
Again, it's fairly easy to cut through the walls to create a window-sized hole. Usually, there is no need to support the rest of the wall as the wall plate carries most of the load, and the straw bales act together as an integral material because of the way they are pinned. Either follow the method above, or you can use a hayknife, even a chainsaw, although power tools like this tend to clog up very quickly. Once you've cut the hole, a structural boxframe can be fixed into the gap, with the window inside this.
Can I use straw to add an extension to my house?
Yes, both loadbearing and framed systems work well here. You may need to think carefully about settlement, and not make the final attachments from the straw to the house wall until after the walls are compressed. You can also easily add an extension to your straw bale house by cutting a doorway through, in the same way as described above for making a window. Families have sometimes encouraged their children to build their own spaces once they've reached a suitable age!
Hackney City Farm – a strawbale extension to an existing building
