WhatHut › Shed bases: which to choose and how to prepare
Shed bases: which to choose and how to prepare
A shed is only as good as its base. A flat, firm, well-drained base prevents rot, sticking doors and a sagging floor.
Why the base matters
Summerhouse24's base guide is blunt: never place a shed directly on grass or soil, as moisture leads to rot and an uneven floor. A good base keeps the floor off damp ground, keeps the shed level and lets air move underneath.
Base types
| Base | Pros | Cons | Approx. cost (per that guide) |
|---|---|---|---|
| Timber frame | Durable, customisable, good airflow | Needs periodic preservative treatment | £100 to £450 |
| Plastic grid (gravel-filled) | Won't rot, drains well, easy DIY | Needs gravel and grid assembly | £80 to £140 for grids plus £40 to £100 gravel |
| Timber skids | Quick, simple, cheap | Not for heavy buildings, needs level ground | £80 to £120 |
| Concrete blocks | Cheap, tough, good on uneven ground | Space them to avoid pressure points | £30 to £90 |
| Adjustable risers | Levels a frame on slopes | Load limits | £120 to £250 |
The guide suggests a timber frame on concrete blocks for the most stable, long-lasting set-up, and skids or plastic grids for a lower budget. A full concrete slab is another common option for heavy workshops and garden rooms, but we did not find details in the sources we opened, so get a quote.
Size
Make the base slightly larger than the shed, roughly 5 to 10 cm extra on each side, which helps drainage around the edges and makes installation easier. Check the supplier's footprint, including any roof overhang or door step. See sizes.
Ground preparation
- Clear the area: remove grass, roots, stones and debris, then rake the soil flat.
- Plastic grid: lay heavy-duty weed membrane, add about 50 to 75 mm of gravel, compact it, then fill the grids with 20 mm clean gravel.
- Concrete blocks: dig pads roughly 30 to 40 cm wide, add compacted gravel to each, and tap the blocks level.
- Soft or soggy soil: usually means a sub-base or raised system, per the guide.
Drainage
Check where rainwater runs during heavy rain. If it flows towards the shed site, consider a slight slope, a French drain or guttering. Gravel layers help water drain away from the base.
Other points
- Plan cable routes before you build if you need power. For electrics in a garden building, see garden offices and regulations.
- Check local planning rules if the base will be raised more than 30 cm. The Planning Portal says platforms must not exceed 0.3 metres in height; see planning permission.
- Frost-proof foundations are mainly needed for sloped sites, colder regions or heavy buildings, per the guide.
- Leave access to the underside so air can flow and you can check for damp.
Tip: get the level right
Use a long spirit level across and along the base. A base that is slightly out of true will warp doors and windows over time. Fix it before the shed arrives.
Prices on this page are typical estimates for November 2026, not quotes. They vary with size, timber grade, supplier, delivery, VAT and installation. Check current prices before you decide.
Frequently asked questions
Can I put a shed straight on grass?
No. Moisture leads to rot and an uneven floor.
What is the cheapest shed base?
Concrete blocks or timber skids are among the cheapest, according to one guide, but suit lighter buildings.
How big should the base be?
Slightly larger than the shed, about 5 to 10 cm extra each side per one guide.
Do I need a concrete base?
Not for most sheds. Heavy workshops and rooms may benefit. Get advice.