Also known as poured adobe or cob, earthen floors embody almost all of the best attributes of ecological building. They are made of widely available, cheap, local materials--clay, gravel, and straw. They work perfectly with passive solar designs, adding thermal mass to the inside of a building where it can store heat accumulated from the sun. They are solid underfoot, but softer than concrete or stone. They are also warmer to the touch than concrete and stone, and are ideal to use with radiant floor heating. But best of all, they are beautiful and comfortable to walk on. Sealed with multiple coats of natural oils their finish color is the same as the wet clay soil they're made from. Chopped straw can be added to the final layer to add depth and texture to the final appearance. Similarly, different colored clays or tints can be used for the final coat to allow a wide range of finish colors.
For buildings without a
basement, standard conventional building practice is to pour a
concrete slab on grade. But as a building material, concrete has
several critical disadvantages. First of all, its manufacture is
extremely energy intensive, requiring massive amounts of fossil
fuels. Because so much of it is produced globally, concrete's
production accounts for 7-10% of all greenhouse gases released into
the atmosphere each year. As a flooring material, concrete is
extremely hard, and therefore very hard on knee and hip joints,
which evolved to handle the stresses of walking and running on soft
earth. A more ecologically sound foundation is a rubble trench
topped by a grade beam. This ancient method was introduced to
modern building practice in the United States by Frank Lloyd
Wright. Inside the beam, layers of drainage rock, gravel, and clay
are built up to create an earthen floor. The same foundation can
also be used with floors of wood, stone, tile, or
brick.
