Bristol Green House Straw


Tyre walls
Straw bale walls
I-beam roof
Living roof
Clay/Lime render


Strawbale wall construction.

Straw is perhaps the ultimate eco-building material with incredible insulation properties and great load-bearing capacity. It’s also like building with giant lego. Let’s play.

Our bales came from Chris Wyatt's farm, 10 miles away, near Nailsea. The bales all come out a slightly different length and this is actually useful whern contructinmg the wall. He set the machine to 'tightest' to make the bales as dense as possible.
Each bale needs to be squared up at the ends in a process called dressing. For some reason on our build it became known as fluffing.
Hazel pegs protrude vertically from the wall plate, two per bale, to a height of less than a single bale height. The first row of bales are pushed down onto these. On the fourth course longer pegs, about 3 bales height in length, are hammered through, two per bale. The same was done again through holes in the bottom of the roof plate. The hazel pegs came from Lower Woods, Chipping Sodbury, care of the Gloucester Wildlife Trust, at a cost of 40p each.
In our build I added vertical oak beams with adjustable bases to be able to even out bale compression over the three walls (each a different number of bales high).
First we sprayed around a guide block, then we cut out the straw using a powered aligator saw. It is possible to do the cutting with a hand saw as well.

The adjustable bolts were made by local blacksmith Fred Brodnax. In a conventional straw bale build these oak beams wouldn't be necessary as straw has great load bearing qualities.
In our build, with only three walls, and each of those of different bale heights, these adjustable bolts will prevent some bales comressing more than others - especially those nearest where the fourth wall is missing.
The bales can be hit very hard to get them to line up. There is a special strawbale persuading hammer that looks like something out of Asterix meets the Vikings. We used a sledge hammer.
Finished back wall seen from inside and out
Side walls interior.
The build
We built all the walls over a four day 'course' run by Lesley Chenery of Amazon Nails. Once trained, putting up bales can be very quick. It's all about the fun of the process. Building with straw is a joyous experience.
The repair
While I was away working two of the walls became saturated with water to the point where the straw began to rot. Although this felt like the biggest disaster possible it was actually easy to remedy. We lifted the roof using acrows, removed the wet bales and replaced them. As we were experienced now, this was done very quickly and every thing was back to sweet smelling straw.
The tweeks
Before we could render or put the soil on the roof there were a number of tasks to be undertaken. First the straw was trimmed. We used an angle grinder with an arbortech blade. Others use strimmers with a metal blade or chainsaws.
Then Barbara Jones came down to do some final straw engineering. Firstly, on the seven bale wall near the front of the building we cut a groove in the straw on the outside to take a scaff plank which we tied, through the bales to an oak beam on the interior. This was done to reinforce the wall and prevent the straw separating from the oak beam, which in this location is sharing the weight of the roof witht he bales. The whole front of the building is a huge window, and this has no structural function, so the seven bale wall at this location is the most vulnerable.
In addition we fitted wooden restraints for the bales on the front walls. In conventional straw bale construction the building has four walls. This one only has three, so the bales here need restraining as they are under such great pressure from the soil on the roof. The top of these restains were notched and held in place so that as the weight was added the roof could descend to it's natural settling point, compressing the bales. It was important that our front braces didn't prevent this compression from occuring.
What I'd do differently...
I would completely recommend self-building with straw and you can be sure that an industrialised version of straw building will become common soon.

The main change I'd make is to build the roof on the ground and hoist that into place first so that the straw walls could be built under the cover of the roof. The roof could then be loaded to compress the bales. This would save all the hassles of trying to protect the bale walls from the elements whilst the roof is being made and make the construction of the roof way easier as it is done on the ground. This method is now becoming common practice.