A bermed building has above-grade walls with earth banked against three sides and the south face left exposed for windows. The banked walls become retaining walls that carry soil pressure, so place the backfill in even lifts on both sides of a corner, keep it away from wall tops until the roof is on, and drain it so the soil stays dry.
Berming is the mildest form of earth sheltering, banking soil against ordinary walls to gain insulation and wind protection.
Berming Turns A Wall Into A Retaining Wall
A wall built to stand in free air has no reason to resist sideways pressure. Piled earth pushes on it. How much it pushes depends on the soil, the height of the bank and above all on water, as the calculations in Earth Load Calculations show. Bermed walls therefore need the same attention as retaining walls: see Retaining Wall Design.
The classic arrangement from the parent article exposes the south face to the sun and berms the other three, giving light and passive solar heating; see South-Facing Glazing and Passive Solar Building Design.
What You Need
- Walls designed for soil pressure, not just self-weight.
- A waterproof layer on the buried face and a drain at the foot; see Waterproofing and Drainage.
- Free-draining backfill next to the wall.
- Clean, sloped berm surfaces so rain runs off and away.
Method: Build The Wall, Then Backfill Carefully
Step 1: Build the wall and waterproof its outer face before any earth touches it.
Step 2: Lay the foot drain at footing level and cover it with gravel.
Step 3: Wait until the roof is on, or the wall is braced, before backfilling. A freestanding wall pushed on from one side can fall inward.
Step 4: Backfill in even lifts, compacting each, and raise both sides of a corner together so the load stays balanced.
Step 5: Shape the surface so water runs away from the building.
Common Mistakes
- Backfilling against fresh masonry. Mortar or earthbag walls need time and bracing.
- Heavy equipment close to the wall. The machine adds a surcharge on top of the soil.
- Puddles on the berm. Water in the backfill can more than double the push on the wall.
Safety
Walls can fall inward during backfill
Never stand between a backfilling machine and the wall. Brace walls before backfilling, keep machinery back from the wall, and dig any foundation trench deeper than about 1.2 m with sloped or shored sides.
What’s Next
- Learn next: Retaining Wall Design — checking the wall
- Combine with: French Drains and Perimeter Drainage — keeping the berm dry