What’s the most efficient, cost-effective way to build with earthbags? How can you enclose the most space with the least time, effort and money? Well, it depends in part on climate, individual skills and preferences as far as styles/building types. (Other factors will be covered in a future post.)
In general, round shapes are the most efficient. They create the most amount of floor space for a given wall length. This is easily demonstrated by drawing a circle and a square using the same lineal distance of walls. For example, draw an 18’ diameter circle, which will have an area of 254 square feet and circumference of about 56.5’. Divide 56.5 by 4 (= 14.1’) to obtain a square with the same total wall length. A square with 14.1’ per side has an area of about 200 square feet. So in this example there’s a gain of 54 square feet of floor space. (Draw this with your kids. It’s a great learning experience.)
So why do builders churn out square/rectilinear structures? Because modern building materials are rectilinear – plywood, OSB, sheetrock, etc. But we know these materials are energy intensive, costly, lead to monotonous designs and have negative impacts on the environment. Earthbag building frees us from these constraints and enables the use of more efficient round shapes. In addition, round shapes are inherently more stable. “Round is sound” as they say.
Size is also important. Large houses require much more time, labor, skill and materials and can easily wear you down, even more so for owner-builders. It’s far better to build only what you need. You can always add on later. Build with cash one stage at a time.
Another factor to consider is fill material – what goes in the bags. Lightweight materials such as scoria are much faster and easier to use than soil. This one factor alone can cut the labor by severalfold, because scoria is lightweight, easy to work with and requires less tamping. Scoria is insulating and so it’s ideal for extreme climates. Plus, scoria doesn’t rot, burn, attract pests, etc. One limiting factor is it’s less stable in certain applications such as straight walls and tops of domes that curve in too quickly.
And the winner is? I’ll give it a tie between roundhouses and domes, depending on the variables listed above. Small to medium sized roundhouses with simple roof designs have an edge in many cases, especially rainy climates and for those with carpentry skills. In dry climates, domes may be more efficient. Organic shapes that approximate circles are a close runner-up, although this often complicates roof construction.