Excavating the Foundation to the Frost Line:
Depending on where you live you will have a choice of building above ground and berming your home (in say rocky terrain where you can’t dig down unless you blast it) or below the surface. Excavating your foundation just below the frost line is preferable by far in order to tap into those stable earth temperatures that the whole principle of the Earthship is based on.
If you are unfamiliar with frost lines because you live somewhere warm and tropical, to you I say, bite me. The rest of us have to contend with the earth under our feet actually freezing to a certain depth which varies from place to place so you must learn what depth to dig to for YOUR area. I live 4000 feet above sea level therefore it’s a done deal that I will have to dig down further than say the ‘Vancouverites living at sea level as the winters here are more severe. Excavate your site just below the depth where the ground would freeze as the earth tends to stay a constant temperature year round above zero unlike the wildly fluctuating temperatures of the air above ground.
Consider this for a moment. When you are hiking in the mountains (have you ever been hiking? If not, you should go-it’s wonderful) and the weather changes every 5 minutes as it does here in beautiful B.C. you can stand out in the open air and freeze your petunias off or you can find a little nook in the depressions of rock in the earth (preferably one bathed in sunlight), nestle into the earth and allow the sun to hit the thermal mass to warm you. If you have an extra layer to put on, that would be like berming your house or as I like to call it, wrapping a blanket around it. Perhaps this analogy is a little silly but you get the point.
Dig down into the earth just below the frost line combined with thermal mass and passive solar heating and you have the makings of a house that regulates itself to approximately 58 degrees year round, even if you don’t spark the fireplace up. How well would your house perform if you couldn’t turn the furnace on? With the rising costs of oil and the uncertainty of global warming, having a home that heats and cools itself based on its design principles is a reassuring and practical way of building and that is an Earthship ‘tip’.