A shed is only as good as the base it sits on. Get the base wrong and doors drop out of square, floors rot, and the whole building twists. Here is the exact spec we recommend — the same one we deliver concrete for across West Yorkshire every week.
The perfect shed base spec
- Excavation: dig out 175–200mm below finished level, removing all topsoil and roots
- Sub-base: 75–100mm of MOT Type 1, compacted with a wacker plate
- Concrete: 100mm of C25, laid in one continuous pour
- Finish: tamped level, edges trowelled smooth
How much concrete do you need?
Multiply length × width × 0.1 (for 100mm). Common shed sizes:
- 6×4ft (1.8 × 1.2m): 0.22m³
- 8×6ft (2.4 × 1.8m): 0.45m³
- 10×8ft (3.0 × 2.4m): 0.72m³
- 12×10ft garden room: ~1.1m³ (consider 150mm/C30 if it is a heavy garden office)
These are exactly the small volumes where volumetric delivery wins: no minimum-load fees, no wasted half-drum, and the mix is fresh because it is made at your kerb. Check your own dimensions with the calculator.
Step-by-step on pour day
- Set level timber formwork around the perimeter, checked with a spirit level
- Lightly dampen the sub-base so it does not suck water out of the mix
- Pour, then tamp with a straight timber across the forms in a sawing motion
- Cover with polythene and leave 48 hours before building; full cure in about a week — see our curing guide
Mistakes to avoid
- Skipping the sub-base — concrete on soft ground cracks, full stop
- Mixing by hand for anything over 0.3m³ — inconsistent strength and it will take you all day
- Pouring onto frozen ground in winter — read our winter pouring guide first
Ready to book? Get an instant price on the quote page or call 01924 910 129 — most shed bases can be poured same-day.
FAQs
How thick should a concrete shed base be?+
100mm of concrete is the sweet spot for garden sheds and summerhouses, laid on 75–100mm of compacted MOT Type 1 hardcore. For heavy workshops with machinery, go to 150mm with A142 mesh.
What grade of concrete do I need for a shed base?+
C20 is adequate for a light garden shed; C25 is our recommendation for anything you care about — it costs only a few pounds more per m³ and gives a harder, more durable surface.
How much does a concrete shed base cost?+
A typical 8×6ft (2.4m × 1.8m) base at 100mm needs about 0.45m³ of concrete. With volumetric delivery you pay only for that exact amount — usually £60–£90 of concrete plus your sub-base materials.
Should a shed base be bigger than the shed?+
Make the base exactly the same footprint as the shed, or up to 25mm smaller all round. A base that sticks out catches rain, which splashes and drains under the shed floor causing rot.