Construction guide

How deep to bury a bunker

There is no single right depth. The engineer sets it from the soil, the water table and what the bunker is for. Here is what goes into that number.

The short answer
  • Burial depth is set by the engineer from the site soil and water table, not picked from a chart.
  • A water table close to the surface pushes up on a buried structure as well as in.
  • OSHA requires a protective system in any excavation 5 feet deep or more, unless it is entirely in stable rock.

What sets the depth

  • Cover. Earth over the roof adds protection and holds the temperature steady, and it also adds weight the structure must carry.
  • Frost. Water lines and the structure itself are kept below the depth where the ground freezes in winter.
  • Water table. The deeper you go, the closer you may get to groundwater. A structure below the water table has to be designed against buoyancy and leaks.
  • Access. Every foot of depth adds to the stair or hatch at the entry and to the emergency exit.

Test before you dig

A site visit with test pits or borings shows the soil type, how much rock there is and where the groundwater sits. Those results set the depth, the bedding under the cubes, the backfill and the waterproofing. The USDA soil survey is a good first look at your parcel, and it flags shallow groundwater, but it does not replace testing on the spot where the bunker will go.

Digging safely

Under OSHA rules, a trench or excavation 5 feet deep or more needs a protective system, such as sloping, benching, shoring or a trench box, unless it is entirely in stable rock. At 20 feet or more the protective system must be designed by a registered professional engineer. Spoil piles stay at least 2 feet back from the edge, and a competent person inspects the excavation before anyone goes in each day.

Questions

Can a bunker go below the water table?

It can, but it has to be designed for it: drainage, waterproofing and enough weight or anchoring to resist uplift. In many cases it is simpler to set the bunker higher and add earth cover above grade.

Who decides the depth for a CUBE Bunker?

The engineer of record for your project, from the site visit and soil results. Every layout gets stamped drawings for its site.

Sources
  1. OSHA: Trenching and excavation safety fact sheet
  2. USDA NRCS: Understanding soil risks and hazards
  3. Conexwest: How deep can you bury a shipping container?

CUBE Bunker prices are preliminary until engineering for the cube system is complete and are confirmed in writing after a site visit. This guide is general information, not engineering, legal or medical advice. Updated 2026-11-02.