Earth Berm

An earth berm is a bank of soil piled against the outside of a building wall. Air temperature swings hard between day and night and season to season, while the ground a little way down barely moves. Burying a wall in soil swaps one for the other: instead of losing heat to a cold night or gaining it on a hot afternoon, the wall trades slowly with a mass near the yearly average. The effect works both ways, so it is as much a summer measure as a winter one.

What makes it demanding is that it reverses the usual rule for ground beside a wall. Normal practice slopes soil away from the wall and leaves its foot bare, so damp and insects can be seen coming. A berm suspends both, and those protections have to be rebuilt by hand: a drainage layer and a waterproof membrane between soil and wall, roof water carried past the far toe of the bank, and the bank dying out against masonry, with no wood or siding where soil can reach it, since buried wood lets termites in unseen. The wall was never built to hold earth back either, which is why this is engineered work.

The failure that catches people is caused by the benefit. A wall held near ground temperature is a cold surface, so warm damp air touching it condenses and the inside face can run wet all summer - and opening a window to dry it makes things worse, because that air is the source of the water. A bank that settles reverses its own slope and ponds water against the wall it protects, and a bare face erodes unless kept under a mulch of wood chips. The membrane behind the bank, not the earthwork, decides how long it lasts, and replacing it means digging the berm off again; the standing work is keeping the buried drainage clear and the foot of the bank visible enough to inspect. A bermed wall admits no sun, so it belongs with glazing on another aspect, mass inside to take up that gain, and a roof overhang to make it seasonal.