Straw Bale House Building.
Building a Green Home.
Here we share our straw bale house building experiences so you can learn about straw bale home construction.
Interested in building a green home? Straw homes are a great option!
Advantages of Straw Bail Homes
Straw homes offer many advantages when building a green home.
1. Straw bale home construction doesn’t require a lot of skill.
2. Straw bail construction is relatively quick and simple.
3. Straw bail houses are naturally well insulated from noise and temperature.
4. Straw bales, once rendered, have a very high fire safety rating.5. If you DIY, straw homes are an inexpensive method of building a green home.
Straw Bale House Building Options
There are two main methods of straw bale home construction – in fill, and load bearing.
Load Bearing Straw Bail Houses
Load bearing means that you create a strip footing for your straw bale walls, build them and then construct a roof directly resting on the bale walls.
The main advantages of this method are:
• It uses a minimal quantity of building materials
• The weight of the roof compresses the bales so there that settling of the structure is quicker. Render applied to the walls is thus less likely to crack over time.
• Building is more straightforward as there are less structural elements to bale around.
The main disadvantages are:
• The bales are open to the weather until the roof is on.
• The need for adequate support sets major constraints to the design – less than 30% of any wall can be open to windows or doors. This makes it harder when building a green home to incorporate solar passive design.
In Fill Straw Bale House Building
With the in-fill method, you first build the main structure/framework and roof for the home, then fill in the wall spaces afterwards using straw bail construction.
Though it uses more materials than the load-bearing approach to straw bail construction, we elected this method because:
• It gave us a sheltered area to store our bales before building.
• It provided a shelter to live in while we built.
• The walls were protected by the roof from rain.
• More costly in materials, and greater ecological footprint.
• More mucking around fitting bales around framing.
• Having to compress down the bale walls manually before rendering.
Our Straw Bale House Building Process
1. Straw Bale House Building the Strip Footings
Once we had put up our shed frame and roof, we started our straw bale home construction by pouring concrete and broken scrap paving into timber formwork.
The footings were built slightly less wide than the bale width to allow trimming the bales back to the footing width.
They were also studded with scrap iron rods to provide a purchase for to secure the first row of bales to the foundation.
To keep the dampness of rain back-splash from the ground away from the straw, we built a brick plinth from recycled fast wall bricks - some people use timber.
We chose bricks to avoid termite problems, save costs, and because it gave us a good height.
The cavity this created was filled with blue metal to provide good drainage should any water find its way into our strawbale walls.
You can lay your electrical cables into the footing before you put the blue metal in if you want.
2. Straw Bale House Building the Straw Walls
It is important not to build the walls too tight, because forcing a bale into one spot just makes somewhere else bulge!
Note that bales have "sides" - one is of the cut edge of the straw sheaf, and the other is the folded edge. The folded edge size is a wee bit thicker than the other.
So one way to ensure a more even wall is to build a row of bales so that the same edge is facing out, then on the next row you alternate so that the other edge is facing out, and so on.
Filling holes and gaps:
With infill straw bale home construction, there are a lot of gaps to deal with!
For small full thickness holes and gaps, simply take a sheaf of straw, fold it in half, then stuff it into the hole from each side, folded edge first.
If you can't stuff them securely, then you can fasten some plaster's mesh to the area using staples for framing, and bits of wire folded into a u-shape for bales. Then you simply stuff the straw behind it.
3. Straw Bale House Building - Preparing to Render
Research has now proven that there is no need to add a layer of wire netting to your straw bail construction. It adds nothing to the strength of your rendering! The straw itself will hold the render for you. Knowing that saved us heaps of money!
Before rendering, we trimmed the straw walls to remove the shaggy bits. At first we tried this hedge trimmer, but found that an angle grinder worked better (it was damp weather at the time - beware of the risk of fire!)
To get a neat finish around windows and doors, we used plaster's mesh before rendering.
4. Straw Bale House Building - Rendering in Lime
Some people render in concrete but we didn't like that idea...
Because it is environmentally costly, financially costly and not very good! No matter what render you use, the first coating will crack due to settling of the bales. Concrete seals so well that any water that undoubtedly will find its way through such cracks into your wall, cannot get out again!
Better options are earth or lime. The earth on our property wasn't highly suited to use as a render, so we opted for lime.
Lime "breathes" allowing a healthier home environment, plus also allowing dampness to escape from the walls. If it cracks, it also apparently "self heals", with a propensity to fill in the gaps itself!
The lime we're using on the first and second coats is a waste product from lime plaster production that we got for free.
We mixed this lime screening waste in the concrete mixer - 1 part (2 shovels) of lime waste to 2 (4 shovels) of coarse sharp beach sand of mixed grain sizes, then added a dollop (about a liter) of proper lime putty to each mix.
You must wet the straw well before putting on the first coat of render, and really push it into the straw. It goes on grey then dries to a beautiful "old-worlde" white lime finish.
We'll let this set for a month or so before rendering with the next "scratch coat" using waste lime again. After this one is applied you hatch it over with scratches to provide a grip for the final coat.
If the weather is hot and dry you need to dampen the render every day for a week or so so that it dries slowly.
After another month or so we'll apply the thin finish coat for which we'll use proper lime putty.
If you don't want to go to all this slow work, you can have the render sprayed on by a contractor.
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