How we built/compressed our external staw bale walls
Over the years a few different methods of building straw bale walls have developed. Some use steel rods, some use wire netting/chicken wire over all the walls, and there are some other tried and true methods as well. We went with Brian Hodge's method (he was also our building consultant throughout the build) which is to use polyester strapping and 'boxing'.
Our photos will help explain......first of all, we laid bottom boxing on the floor, putting the polyester strapping underneath the boxing as shown right.
Then we filled the boxing with insulation, and put a lid on it, hence the term 'box'.
This bottom boxing is what the bales were laid straight onto, just like bricks, in running bond. Straw has a fluffy side and a spikey side, and we alternated with each row ie fluffy one row, spikey the next. Then once the bales were at a specific height, (not all the way to the top), we put an intermediate boxing on top of it.
Many houses may not need intermediate boxing, they just have a bottom and top boxing. But, because the tops of our walls are all on different angles ie not horizontal (a clerestory house will do that) and we had gable ends, we needed a way to compress the walls with equal pressure across it. This was achieved using intermediate and top boxing to compress the walls.
You can see from the photos, the orange strapping going over the intermediate boxing (horizonatal) and the additional strapping going over the top boxing.
In terms of the compression of the walls, once the intermediate boxing was in place, we strapped the walls down and compressed them. This is done using some fabulous clips, and some compression clamps.
The intermediate straps were compressed over 3 days, and this compression is extremely effective in providing strength and stability to the walls. Our walls are not load bearing, but are termed 'structural infill' and they help to keep the house together laterally, rather than holding the roof up.
Once the intermediate boxing/walls had been compressed, we added more straw bales on top if the intermediate boxing, put the top boxing on and and compressed that section over the top of the other strapping. The photo above shows this really well.
Having the two sets of boxing and compression may not seem like much more work, but it was significant. Intermediate boxing added significant time (and costs) to the walls, something we did not know when we designed the house. Having said that, we love our walls, and it was all worth it!