Foundations for a 20' Container: Gravel, Blocks or Concrete?

A container doesn't need a fancy foundation, but it does need a good one. Set a container on soft, uneven ground and it sinks at the corners, twists so the doors won't close, and rusts from underneath. A few hours of prep avoids all of that.

Here are the main foundation options for a 20ft container, how they compare, and how to choose. Do this before your 20' shipping containers for sale near me delivery arrives, so the driver can set the container straight onto a ready base.

What a foundation needs to do

• Keep it level, so the doors open, close and seal
• Spread the weight at the corners, where it sits
• Keep the steel off wet ground, so the base doesn't rust
• Let air move underneath
• Shed water away from the container

A container's weight sits mostly on its four corner castings, so the corners matter most.

Option 1: Compacted gravel pad

A layer of crushed gravel, compacted and leveled, slightly larger than the container's footprint.

• Pros: drains well, easy to level, keeps weeds down, inexpensive
• Cons: needs compacting properly or it can settle
• Best for: most storage containers on residential and commercial sites

How: remove topsoil and grass, add a few inches of crushed gravel, compact it and check it's level. A slightly larger pad also gives you a clean area in front of the doors.

Option 2: Concrete blocks or pads under the corners

Solid concrete blocks or precast pads placed under each corner, and sometimes at the middle of each long side.

• Pros: quick, inexpensive, lifts the container off the ground for airflow
• Cons: each block must sit on firm, level ground, or it will sink
• Best for: firm ground, temporary or semi-permanent storage

Tip: set the blocks on compacted gravel for a firmer base.

Option 3: Railroad ties or timber beams

Treated timber beams laid across the ground under each end of the container.

• Pros: easy to level, spreads weight, affordable
• Cons: timber eventually rots, especially on wet ground
• Best for: temporary placements and firm, dry ground

Option 4: Concrete piers

Concrete footings poured below ground at each corner, sometimes with steel plates to weld or bolt the container to.

• Pros: very stable, good for frost-prone ground, can anchor the container
• Cons: more work and cost, and needs accurate placement
• Best for: permanent installations, offices and homes, windy or seismic areas

Option 5: Concrete slab

A full concrete slab under the container.

• Pros: the most stable and long-lasting, easy to keep clean around
• Cons: the most expensive, and the container sits flat on concrete, so plan drainage and airflow
• Best for: permanent workshops, offices and multi-container sites

Comparison

Leveling tips

• Check level along the length and across the width.
• A very slight fall toward the doors, if your site allows, helps rain run off the roof and away from the floor.
• Re-check after heavy rain or the first frost in the first year.
• If the doors start to stick, the container has probably shifted out of level.

Drainage and placement

• Don't place a container in a low spot where water collects.
• Keep it clear of septic tanks, drain fields and buried utilities.
• Leave room around it for airflow and maintenance.
• Make sure the delivery truck can reach the pad in a straight line.

Frost, mud and slopes

Frost. In cold climates, ground can heave as it freezes and thaws, lifting one corner more than another. Gravel drains better than soil and reduces heaving; for permanent installations, concrete piers set below the frost line are the most stable option.

Mud. Clay and wet soils lose strength after rain. Dig out soft material and replace it with compacted gravel, and avoid deliveries when the ground is saturated.

Slopes. On a gentle slope, build up the low side with compacted gravel or use taller blocks or piers so the container sits level. On a steep slope, you may need a retaining edge or an engineered base, so get professional advice.

Permits

Storage containers on simple bases often need no foundation permit, but permanent installations, offices and homes usually do, and may need engineered foundations. Check with your local building department.

FAQ

Do I need a foundation for a 20ft container?

You need a firm, level base. For storage, compacted gravel or concrete blocks under the corners are usually enough.

Can I put a container directly on grass?

It's not ideal. The ground can sink unevenly and the base stays damp. At least put blocks or pads under the corners.

How many blocks does a 20ft container need?

At least one under each corner. On softer ground, add support at the middle of each long side.

Should a container be perfectly level?

As close as possible, so the doors work properly. A very slight fall toward the doors helps drainage.