What kind of house insulation is free? Dry earth!
- available to everyone for almost nothing.
Free house insulation: It amazes me that, in some cases the solution to a problem lies literally right under our feet.
In this case, I mean earth as insulation. I know folks have built underground houses and earth sheltered houses, but really, they do not necessarily exploit the potential that plain earth has for insulating our houses.
What am I talking about? I mean earth if properly used has high and very useful value as insulation. I suspect chipmunks, ants, groundhogs, rabbits, any animals that burrow into the earth have known this for years (or a few millions of years) while we, the smart ones (ha!) until now have not realized the potential, and pay money, and build factories for something anybody with access to a pile of dirt can get for nothing.
Now let me clarify. To work well as insulation the earth must be properly used. A pile of earth, or the earth on top of an underground house will not work. To provide real insulating value the earth must be loose and dry. Animals know this. The shelters they dig to stay warm in cold weather are always into dry and well drained soil, with a topping of roots leaves, preferably sloped so water drains off and does not penetrate into their sleeping (and living in the case of ants) chambers.
How good is earth as an insulator? In David Wright's book 'Natural Solar Architecture' page 94 the insulating values of various materials are listed. Earth (dry) is listed as R 2.22 per inch. this compares to wood at R 1.25 per inch (as in log cabins) and fiberglass batts (that itch and may cause cancer) at R 3.17 R per inch. Higher R number means higher insulation value. Considering that it is free, R 2.22 for earth is good, plenty good enough for many applications.
One foot of dry loose earth provide an insulation value of R 27 - better than 8 inches of irritating fiberglass in a conventional wall. The fiberglass insulated wall must be built thick enough to accommodate 8 inches of fiberglass. The earth insulated wall will have to be a little thicker, but the insulation inside will cost nothing. The extra weight of a dry earth insulated wall may cost a little more in the form of ties between inner and outer walls, and an inner wall of more than drywall - an osb board underlayment could be used.
The key is that the earth must be kept dry. A house using earth as insulation must be designed so the earth stays dry. A berm against a house wall, or a house with earth overhead as in an 'underground' may not be good enough. Earth - saturated with rainwater or snowmelt or water from the ground moving up by osmosis, or from inside the building as warm moisture laden air moves out (through cracks, pores, joints in walls - has almost no insulation value.
Earth used to insulate walls must have vapor barriers all around - and drainage openings in the base to let any moisture that works into the wall a way to escape.
To achieve this is not difficult or expensive. Plastic sheeting buried and not exposed to sunlight can last indefinitely. Even plastic shopping bags obtained for free will work, Above, a roof overhang should extend far enough to cover the wall top and keep dripping water off the roof away from the base of the wall. I suggest that the outer surface of this earth wall have stones / rocks set into it for protection with a plastic barrier behind them.
Earth can be used as ceiling insulation. The ceiling will have to be built with more reinforcement than conventional construction to hold the extra weight. But if the earth is kept loose and dry it will not be excessively heavy. An underground house, where the earth overhead can get wet, or even saturated must have a massively reinforced roof to hold the weight of water.
Earth used as ceiling insulation can be kept light by mixing in leaves, sawdust, twigs, grass, weeds, all manner of organic material - resembling, perhaps the soil of a forest floor. (The soil of a forest floor, protected by a layer of leaves and thus keep dry may barely freeze in winter, providing shelter for all manner of creatures living under the forest floor).
To prevent fire danger organic matter should be, I believe, well mixed into the earth. Also, I would not use topsoil for ceiling insulation. Topsoil belongs in your garden or greenhouse. Sand, clay and subsoil would be better.
In a fire, if the walls and ceiling burn and collapse, all of the soil above and to the sides could fall and smother the fire - serving as a natural means of fire control.
Hobbit house anyone?
A roof growing grass, and with earth used as ceiling insulation for the house below, must have that insulation properly protected from water. Therefore, under the grass and topsoil layer must be placed plastic sheets or vinyl sheets, or both, or perhaps metal sloped to drain water falling on the grass layer away from the dry earth below - just like the leaves on a forest floor. So perhaps we see how a hobbit house might be properly designed to be warm dry and snug - and maybe J.R.R. Tolkien imagined more than he knew.
The body heated space diagrammed on the first page of this blog could be modified to make use of free earth insulation - with full earth berms on three sides and a roof overhang to protect it. Thus no insulation need be purchased or installed. Insulation could come from earth dug on the building site!
