There are four ways to shelter a building with earth: pile earth against the walls (bermed), put earth on the roof, excavate a pit and bury the structure (cut-and-cover), or build into a hillside and use the slope as the rear and side walls. Each trades more thermal stability and weather protection against more water, structural and ventilation difficulty.
Earth-sheltered design is a spectrum from earth banked against a wall to a fully buried room.
The More Earth Around The Building, The More It Helps And The More It Costs
Below about 2 m the ground stays near the annual average temperature, so the more of a building sits in the ground, the steadier its temperature. The cost of that steadiness is that earth is heavy and wet. The more earth around the building, the more water it must keep out and the more load its walls and roof must carry. The four approaches are:
| Approach | What it is | Main trade-off |
|---|---|---|
| Bermed | Above-grade walls with earth banked on three sides, south face open | Walls must resist soil pressure; see Bermed Walls |
| Earth-covered roof | Ordinary walls, earth-topped roof | Moderate benefit; roof must carry the load; see Earth-Covered Roof Living Spaces |
| Cut-and-cover | Excavate a pit, build inside, cover with earth | True underground; deep excavation and full waterproofing; see Cut-and-Cover Method |
| Hillside | Build into a slope, using the slope as walls | Very effective; water drains toward the building; see Hillside Integration |
Fully underground structures combine the hardest cases of all three problems; see Fully Underground Structures.
What You Need
- A site with well-drained ground and a water table well below the floor.
- A source of structural material strong enough for the soil loads.
- A drainage and waterproofing plan before any wall is built.
Method: Choose By Climate, Site And Skill
Step 1: Check the water table. If it is within 1 m of the planned floor level in any season, do not build underground at that site.
Step 2: Check the soil. Expansive clay swells when wet and can crush walls. Sandy or gravelly soils are better.
Step 3: Pick the approach by how much risk you can manage: berming and earth roofs are gentler than full burial.
Step 4: Plan drainage first. See Waterproofing and Drainage.
Common Mistakes
- Choosing full burial for its looks. It is the hardest option to waterproof.
- Ignoring ventilation. See Ventilation and Light.
- Under-building the roof. See Structural Considerations.
Safety
Excavation and roof loads kill
Digging below about 1.2 m needs sloped or shored walls, and earth-loaded roofs fail with no warning. Both are covered in the articles linked above; read them before breaking ground.
What’s Next
- Learn next: Waterproofing and Drainage — the make-or-break issue
- Combine with: Permanent Settlement Site Selection — picking the ground