Looking for an affordable, sustainable construction method you can use to easily build your own home or guest accommodation on your farm? Look no further than the straw-bale construction technique. Abré Steyn explains how to do it.
“A man’s home is his castle.” I’ve lived in many houses in my life, some beautiful, some downright awful, but none perfect. The worst were government houses unsuited to the climate.
READ MORE: Advantages of building with straw
In Waterval Boven, where a shady lawn could still be iced over by 11am, I lived in a freezing asbestos prefab. The same material was also used for the low roof of our official oven-house in the steamy heat of Zululand.
I suffered from chronic bronchitis in the first house, and teetered on the brink of heat exhaustion in the second.
Everyone has their own idea of what a dream home would be. Mine is cosy and warm in winter and cool in summer, without artificial air-conditioning or climate control. It must be affordable, environmentally friendly and easy to owner-build.
If I ever have the chance to build mine, it will be a straw-bale house. Main house aside, straw bales are also ideal for guest accommodation on game farms, angling lodges or holiday resorts, as well as worker and other cost-effective housing.
This system of construction is ideal for the do-it-yourself builder. Straw is easy to work with as it’s very forgiving, flexible, quick and economical, and it makes a comfortable home for all seasons.
Straw bale homes can be beautiful, with graceful curves, delightfully wide window seats and exciting sculpture and mosaic patterns integrated into the plaster.
If you’re artistic, it’s easy to incorporate these aesthetic elements when building by hand, using what Mother Nature provides.
Rough edges on bales can be trimmed with a chainsaw.
Straw bales are becoming a viable alternative construction material in South Africa. Cape Town architect Etienne Bruwer was a straw-building pioneer, using it to build his office in Constantia, Cape Town. Since then, many straw bale houses have been built in this country.
Security isn’t a problem in a straw bale building. The bales are “nailed” together with reinforcing-rods, and compacted straw takes far more time and effort to break through than any brick wall does.
Tips on building with straw bales
Many people have preconceived ideas about building with straw bales, but here are a few pointers to set your mind at ease.
1. The first factor is the quality of the bales.
- Baled wheat straw is commonly used in the US, with its vast agricultural sector. Source material locally if you can, to reduce transport costs.
- Our vast areas of thatching grass, if cut after the first frost and thoroughly dried, will work if baled tightly in rectangular block-bales.
- The ideal bale consists of clean, dry and densely packed straw with a high stalk and cellulose content. It must be firm and heavy, and resistant to deformation.
- To bale wheat straw for building, combine the grain just below the seed head, then mow the stalks close to ground level for the longest stalk-fibre material.
- Bale it as tightly as possible without bursting. Ideally, use polypropylene baler twine, as wire could rust.
2. Precompression is key
- Precompression, using a car jack, a section of plywood and a piece of plastic to help slide the bale, is the way to go for load-bearing buildings where the bales directly carry the roof’s weight.
- Even in non-load bearing applications, precompression can size the wall to 3cm to 5cm less than the expected height of the bales.
- Compressing bales adds strength to the wall and keeps them from slipping against one another.
READ MORE: A fire-proof house made of straw
3. Get strong walls and a protective roof
- The inevitable spaces between bales need filling, especially at the corners. Stuff deep cavities with dry straw and then start adding clay to the straw so that the final filling has a high clay content.
- Worked into all spaces between bales, it will dry to a strong, firm surface that can be plastered for great durability.
- Use earth, clay or cement to plaster the walls.
- A wide roof overhang will further protect the wall. With an earth or clay exterior plaster, an 80cm overhang for a 3m-high wall is the minimum for frequent driving rainstorms. A gabled roof with its overhang 5m to 7m high will provide almost no wall protection. A porch, veranda or trellis blocks rain and breaks up wind.
A load-bearing style straw bale house in Australia under construction. The roof rests directly on the straw walls. It was built by a family and some of their friends.
- Water running off the window can damage the plaster below it, but an ample window sill that sheds water away from the building will protect the plaster and prevent leaks.
- To protect the straw wall from rising damp, place the bottom bales on heavy-duty polyethylene damp-course. The contact with the concrete foundation and floor helps the straw bale home keep cool in summer and warm in winter.
READ MORE: Straw bale homes Q&A
4. Problem areas to watch out for
A problem area is the interface between the straw and other materials, such as wood. Air will infiltrate the house at the edges of doors, windows, ceilings, foundations and wall sections, lowering the effectiveness of insulation. Here’s what to do about this:
- Careful plastering at these points can help, but drying and temperature changes can cause shrinkage and cracks. To plaster over wood or other material, first cover it with hessian.
- Some straw bale building manuals suggest wire netting or chicken wire, but unless using machine-applied plaster, avoid these as they are a pain to plaster around.
- Rather staple the hessian to the wood using a staple gun, overlapping it 10cm over the straw, and stitch it onto and through the straw with a long home-made bale needle.
- Then coat it in clay and embed it in the infill coat of plaster. The hessian forms a strong fibre framework, preventing the plaster from cracking.
This article was originally published in the 08 October 2010 issue of Farmer’s Weekly.