Building homes out of straw bales doesn’t sound like the best idea, but these houses are environmentally friendly, warm and built to last. We’re looking at how to build a small straw bale house and what that involves.
We’ll examine the different designs of straw houses and what the process of construction is.
What Is A Straw Bale House?
A straw bale house is one that uses bales of straw as either insulation or as building blocks.
There are other materials used in the construction of a straw bale house such as concrete foundations and a timber built roof. But the straw bales constitute the largest percentage of the building materials used in one of these houses.
This kind of construction is gaining popularity due to its environmentally friendly methods, materials and financial savings.
There is a decreasing availability of lumber which causes the price of timber to rise. Meanwhile, straw is readily available as a byproduct of harvesting grains such as wheat, oats, rye and barley.
At this point it is worth clarifying that straw and hay are two different things. Straw is the stalk that is left after wheat, oats, barley or rye is harvested while hay is grass that has been cut and allowed to dry.
Types Of Straw Bale Construction
There are two types of straw bale construction, load bearing and post and beam infill.
In a load bearing straw bale house the weight of the roof (see also: What Is A Pergola?)is supported by the density of the stacked bales. However the size of these houses are limited by building code which only allows 25 feet of unsupported wall.
Also these homes can typically be only one story high.
Post & Beam Infill
A post and beam infill house is one where the load bearing is taken on by the posts and beams which make up the frame. The straw bales are the infill and provide the screening, insulation and shape of the house rather than taking the weight of the roof.
How To Build A Straw Bale House
To build a straw bale house you will need to decide which type of construction you are going to choose.
Foundation & Toe-up
With either type of design there will be a need for a foundation, but also something called a toe-up which is a raised timber channel that keeps the straw bales off of the ground.
Toe-ups are attached to the concrete foundations. The channel is also filled with gravel or stones.
By keeping the bales raised several inches above the ground they won’t soak up moisture. Pins or rebar are inserted into the toe-up and the first course of straw bales is pushed onto them.
This holds the first row of straw bales in place and provides stability for them.
Building The Walls
Subsequent courses of bales are stacked on top of the first row in a staggered brickwork manner for strength. To notch the bales around the posts of the house frame many people use an electric chainsaw.
Alternatively a reciprocating saw or hand saw can be used.
This method is also used to create features such as window seats or cabinet voids within the straw bale walls. For heavier cabinets pieces of lumber with spikes are inserted into the bales and used to support the cabinets.
Some methods of construction incorporate metal lath strips which attach the corners of the bales to the posts of the house frame.
Windows & Doors
To fit windows into the straw bale walls, wooden frames are built with holes drilled into the sides. Then a long bolt is screwed through the hole and into the bales to secure it in place.
Doors are fitted in much the same way as they would be in a conventional house, fixed to a frame. In this case a wooden frame that has been secured to the floor and to the straw bales at the sides and top.
For a small straw bale house you will probably only have a front door for access and maybe three or four windows, depending on your design.
Once all the straw bales are in place they can be pinned down with long bamboo poles or steel rods. These are driven through the bales to hold them together.
To protect the walls from moisture they are plastered inside and out but with different types of plaster. The first coat of plaster is worked into the straw and is followed by two more coats.
On the outside a lime plaster is used to protect the house from the elements. Inside a gypsum or earthen plaster can be applied. The important thing to remember is that the walls of the straw bale house need to ventilate.
For this reason a waterproof barrier should never be used on straw bale walls. Neither should you use a plaster that is waterproof, and all paint should be breathable. Trapping moisture in the straw will cause mold and the straw will start to rot.
Problems To Avoid
Moisture in the straw must be allowed to ventilate, so it is important to keep all the materials that are going on top of the straw breathable. This includes the plaster and the subsequent paint coat.
Storing the bales under cover as you build is a wise precaution as putting damp bales into your walls is not a good idea.
Remember as well as the toe-up to keep the straw from getting wet from the ground to include an overhang in your roof design to protect the walls as much as possible. And remember to seal around windows and doors after installation.
Keep an eye on the plaster so that you can address any cracks immediately should they appear. Cracks can let moisture in and allow it to accumulate.
We hope you have enjoyed this guide on how to build a small straw bale house and that it has inspired you to pursue your build using straw bales.