Concreter › Garage and shed base costs and thickness
Garage and shed base costs and thickness
A shed or garage base is a small job, but the cost depends on size, thickness and the ground. Here is how to work out the concrete you need and what to expect to pay.
Prices on this page are typical UK ranges and estimates as of November 2026. They vary by region, access, ground and the day you ask. Treat them as a way to spot an odd quote, not as a quote.
Shed base: how thick?
Tradespeople answering a MyJobQuote question suggested at least 100 mm for a garden shed, with many preferring 150 mm and some going to 200 mm for longevity. Sub-base advice ranged from about 75 mm to about 150 mm of compacted hardcore or crushed stone. Opinions on mesh also differed: one groundworker said an 80 to 100 mm slab for a shed does not need reinforcement, while others recommended A142 mesh. That disagreement is honest: a small, light shed on firm ground needs less than a heavy workshop. One contributor said clay subsoil and nearby trees are good reasons to talk to a structural engineer.
Garage base: a different job
A garage holds a car, tools and often walls and a roof that need proper foundations. A garage floor slab is thicker and stronger than a shed base, normally laid to a specification from the builder or designer. One UK guide suggests the C25 grade for shed bases and garage floors. If the garage is a new building, see footings and foundations, and ask building control what applies.
Working out how much concrete you need
Multiply length by width by depth, all in metres, to get cubic metres. Add about 10 per cent for waste and uneven ground. Examples (our arithmetic, before the 10 per cent):
| Base | Size and depth | Concrete |
|---|---|---|
| Small shed | 2.4 m × 1.8 m × 100 mm | 0.43 m³ |
| Medium shed | 3 m × 2.4 m × 100 mm | 0.72 m³ |
| Workshop | 4.5 m × 3 m × 150 mm | 2.03 m³ |
| Single garage | 6 m × 3 m × 150 mm | 2.7 m³ |
What it costs
A tidy way to estimate is to take the area and use the per square metre rates for slabs on the driveway cost page (about £60 to £130 per m² fitted in the guides we read). A 3 m × 2.4 m shed base is 7.2 m², which gives roughly £430 to £940 on those rates. Small jobs often cost more per square metre because the contractor's fixed costs (travel, setting up, minimum concrete delivery) are spread over less work. Treat that as an estimate and get quotes. If you supply the concrete yourself, the numbers below matter.
Concrete supply costs for small bases
Less.co.uk's guide, which we read in November 2026, says ready-mix is about £105 to £170 per m³ with a minimum delivery charge of £150 to £250. It says volumetric (mixed on the lorry to order) suits roughly 0.5 to 2 m³ at about £100 to £160 per m³, and bagged concrete costs around £500 per m³. For a 0.43 m³ shed base the minimum delivery charge can cost more than the concrete, so bagged or hand-mixed is often cheaper for the smallest bases and volumetric for bigger ones. See ready-mix, volumetric or DIY.
Getting the base right
- Size. Make the base slightly larger than the shed footprint, or exactly the footprint if the maker says so. Follow the shed supplier's instructions.
- Level and falls. The base should be flat where the shed sits, with water able to run away from it.
- Ground. Strip topsoil and roots. Compact the sub-base in layers.
- Edges and damp. Keep timber floors off wet concrete. One tradesperson suggests setting the shed on blocks or slabs to lift the floor timbers.
- Curing. Do not load the base too early. See curing and cracking.
Outbuilding rules
A base may be allowed without permission even where the building on top needs checking. Rules on outbuildings depend on size, height and distance from boundaries, and differ in conservation areas. Check the Planning Portal or your council before you build. This is general information, not professional advice.
Frequently asked questions
How thick should a concrete shed base be?
Tradespeople in one UK Q&A suggested at least 100 mm, with many preferring 150 mm. Heavy sheds and weak ground need more thought.
Do I need mesh in a shed base?
Opinions differ. For a light shed on firm ground a thin unreinforced slab is often used; others recommend A142 mesh. Ask your contractor.
How much concrete for a 3 m by 2.4 m shed base?
At 100 mm thick it is about 0.72 cubic metres, so allow around 0.8 m³ with waste.
Is a concrete base better than slabs?
Concrete is flat and permanent. Slabs on a compacted base are easier to alter and to remove. Which is better depends on the shed size and ground.