This article describes a low cost method of building insulated basement walls without concrete, using geotextiles. Typical basement walls are expensive and use large amounts of concrete, a major contributor to global climate change. Concrete basement walls are typically built by contractors, because they require expensive forms and specialized knowledge. Plus, in cold climates they require insulation to reduce heat loss. Rigid foam board insulation is most commonly used to insulate basements, but this unfortunately has an environmental toll. All these things lead to expensive, energy intensive basement walls that strain the environment. Obviously there’s a need for low-cost, more sustainable alternatives.
The earthbag/geotextile basement wall system described here has excellent potential to save on initial construction costs and long-term energy costs. And again, no concrete is used. However, this system is experimental — none have been built yet. Even though it is untested, the basic concept utilizes well-proven geotextile retaining wall technology. The same principles have been used to build retaining walls along roads, highways and elsewhere for decades. But no one, to my knowledge, has used this technology for basement walls.
The main components of this basement wall system include:
- vertically stacked, woven polypropylene bags or tubes filled with crushed and cleaned half-inch lava rock (scoria) for insulation
- two strands of four-point barbed wire between each course of bags to prevent bag slippage and add tensile strength
- horizontal layers of mineral subsoil in 5-inch lifts compacted with a vibratory plate compactor
- geotextile fabric (silt fence, etc.) every 10 inches in height: place fabric under the bags and extend 3 feet horizontally
- 6 mil polyethylene moisture barrier placed as shown in drawing
Features include underfloor scoria or perlite insulation, French drain, and simplicity of construction suitable for most DIYers. Non-concrete floor options include lime-mortared stone or recycled brick set on a bed of sand.
No building system is perfect. This basement wall system requires additional excavation, about 3 feet extra width on each side. And, because it hasn’t been built before, there is some risk. More experimentation and research is called for. Hire an engineer with experience in geotextile retaining walls.
Another possible low-tech earthbag basement wall design uses lime, cement or alker stabilized earthbags stepped at an angle.
Drawing by Owen Geiger
Silt fence synthetic fabric
Perlite floor insulation: The Last Straw Journal, issue #60