Friday, November 11, 2005

Earthbag Foundations

Earthbag foundations offer many advantages over reinforced concrete foundations and work well with many types of sustainable buildings. In particular, they are low-cost, fast and easy to build, require no cement (a major cause of global warming), and require no forms or expensive equipment.

Earthbags are simply polypropylene sandbags (or rice bags) filled with soil, sand or aggregate obtained from or near the building site. Unlike adobe or rammed earth, which require a rather specific mix, almost any type of soil or aggregate will work (expansive clay soils are not recommended for foundations). Aggregates are preferred for foundations because they will readily drain away any moisture and prevent wicking into the wall system.

Designed to control flooding and resist explosives, earthbags are amazingly strong, durable and versatile as long as they are protected from direct sunlight. Keep earthbags tarped until they are plastered.

Some typical uses include:
1. earthbags on a rubble trench foundation in mild climates (to raise wall system above grade)
2. aggregate-filled earthbags starting below grade and extending well above grade in flood-prone areas (reduces risk of the structure being undermined – example: a rubble trench could get scoured away and soil-filled bags on lower courses could dissolve)
3. earthbags filled with scoria (lightweight volcanic aggregate) in cold climates (example: scoria-filled bags are equivalent to a frost-protected foundation, and therefore eliminate the need for rigid foam insulation and extensive excavation)
4. scoria-filled bags in desert regions or tropical climates as a cooling strategy

For more information:
Earthbag building information at