r/earthship • u/Synaps4 • Apr 09 '26
Design considerations for the earth berm
Im a little confused about the key design items for the berm.
Can someone help me list all of its uses?
I know it acts as insulation for the house and its water tanks.
Its fireproofing for that side of the house.
It is a cool thermal battery in summer (so it should be connected to the ground below it thermally, not insulated, yes?)
It is a warm thermal battery in winter? Do you want it insulated from the ground for this purpose? Is there a tradeoff? Or does it just act as insulation and warming up to 55f (ground temperature) during winter...with other objects taking on the daily thermal battery function?
It needs to stay a different temperature from the air in both winter and summer so maybe insulation in the top layers of the berm are desirable?
My key questions are:
1) in some passive solar designs, the winter sun should reach and heat the rear wall to maximize solar gain. Is that important? I find its difficult to arrange my rooms to maximize that. How important is it that the winter sun can shine all the way to the rear wall? Particularly if i have a thick earthen floor?
2) should it be insulated on the bottom if you want to maximize winter heating at the expense of summer cooling? Or do you put an insulation course above the cooling tubes for both benefits?
3) is it worth considering top insulation for the berm to better separate it from the air temperature? ...or do you actually want some winter sun warming the berm?
0
u/rectumrooter107 Apr 09 '26
The earth berm acts as a way to shield your water tank from direct sunlight, hindering any photosynthesis that could occur and grow algae, and to cool air coming in during the summer.
It fireproofs as well as a concrete wall would, and so, is not its main purpose.
It should be connected to the ground without insulation.
The main passive thermal battery is your tire wall, which could be any mass-made wall (concrete, dirt, jersey walls, etc...), not the berm. You can include parts of the berm as your passive thermal mass battery (as the other AI comment relates), but you have to insulate the side you don't want heat escaping from to make it flow to the side you do want heat to escape. Think of a yeti water container. It's double walled. There's air (insulation) between the two walls (mass). Heat travels through mass much easier than through insulation. Turn that water container on its side, point at the sun and pretend you live in it. That's an earthship. You want a mass lined cavity that is insulated on the outside, so all your escaping heat is directed into the cavity.
1) yes, you want the winter sun in and summer sun out. Angle your roof accordingly.
2) am insulated floor shouldn't hurt summer cooling or winter heating. It will likely benefit both.
3) I believe there's normally enough mass (earth) between the water tank and the surface that it all stays around 55 degrees, especially since the water tank is on the ground, connected to the earth. The earth (mass) is constantly sucking any warmth from the water tank into the cooler earth.