A fully underground building has earth on every side, so every surface needs drainage and waterproofing, the roof must carry the full soil load, and the air must be changed by ventilation shafts because carbon dioxide pools in low spaces. Do not build one where the water table comes within 1 m of the floor in any season, or in expansive clay.
A fully underground structure is buried on all sides and usually reached by an entry ramp, steps or a tunnel, with light and air brought in from the surface.
Burial Collects Every Problem Of Earth Sheltering In One Room
A fully buried building has the steadiest temperatures, and the least visible profile, and also faces every hazard of earth sheltering at once. Water presses on the roof and every wall. The roof carries earth, rain-soaked earth and anything above. The air has no natural supply, so ventilation is mandatory; carbon dioxide is heavier than air and pools at floor level, and in some geological areas radon accumulates as well.
The tests for a suitable site come from the parent article: the water table must stay below 1 m under the floor in any season, and expansive clay soils, which swell when wet and can crush walls, are a poor choice. Sandy or gravelly soils are better.
What You Need
- A site that passes the water table and soil tests.
- A structural shell sized for the soil load; see Earth Load Calculations and Roof Structures for Earth Loading.
- Waterproofing and drainage; see Waterproofing and Drainage.
- An intake and an exhaust shaft; see Ventilation Shafts and Chimneys.
- At least one exit route that does not depend on the main entrance.
Method: Plan Around The Hazards
Step 1: Check the water table through the wettest season, not just when you dig.
Step 2: Design the shell for soil, saturated soil and any live load on top.
Step 3: Provide two ventilation points, one low for intake and one high for exhaust.
Step 4: Plan a second way out in case the first is blocked by a collapse or flood. This is a general safety principle, not a figure from the parent article.
Step 5: Check the air with the way you sleep and cook in mind: no combustion without a flue and fresh air supply.
Common Mistakes
- Treating ventilation as optional. Moisture, carbon dioxide and radon all build up in a closed space.
- Building below the wet-season water table.
- A single exit.
Safety
The air underground can be unfit to breathe
Carbon dioxide is heavier than air and pools in low spaces; burning stoves and lamps add carbon monoxide; see Carbon Monoxide Risks. Never test the air with a flame. If anyone feels headache, drowsiness or confusion, get everyone into fresh air at once. Excavation deeper than about 1.2 m needs sloped or shored walls; see Cut-and-Cover Method.
What’s Next
- Learn next: Cut-and-Cover Method — how to build it
- Combine with: Storm and Fallout Shelters — a common use