The base is the bit people rush — and the reason most sheds end up wonky, damp, or sinking. Get it right and everything else is easy.
To build a shed base: mark out an area the size of your shed, dig down about 150 mm, lay and compact 100 mm of MOT type-1 hardcore, then finish with paving slabs on sharp sand (most sheds) or a concrete slab (workshops and big sheds). It must be firm, level, square and free-draining.
A shed is only ever as good as what it sits on. A base that's out of level gives you doors that won't shut and walls that won't line up; a base that traps water rots the floor from underneath within a couple of winters. None of it is hard — it's just groundwork, and groundwork rewards patience over muscle.
Four options cover almost every garden. Pick by your budget, the size of the shed, and how level your ground is.
The default for a standard garden shed. Cheap, DIY-friendly, removable, and solid for anything up to about 10×8ft. Our recommended starting point.
Best for: most sheds
The permanent option. More work, but rock-solid and level forever — the right choice for workshops, offices, or any shed you'll spend real time in.
Best for: workshops, big sheds
A treated-timber frame on a bed of compacted gravel. Quick, forgiving on slightly uneven ground, and keeps the floor up out of standing water.
Best for: sloped or soft ground
Interlocking plastic grids filled with gravel. The fastest no-dig option for small, light sheds on reasonably level ground — but only as level as the ground beneath.
Best for: small, light sheds
The most popular method, and the one to learn. You'll want a long spirit level, a rubber mallet, and a hired plate compactor for the day.
Knock in four pegs and run string lines to the shed footprint (or up to 50 mm bigger all round). Measure both diagonals — when they're equal, it's square. This one check saves you a world of pain later.
Lift the turf and dig out about 150 mm of soil across the whole area. Pull out roots and big stones. Unglamorous, but it's the foundation of the foundation.
Spread 100 mm of MOT type-1 hardcore and compact it hard with a plate compactor. Don't skip this. It's what stops the slabs sinking — and it's the single most-skipped step in shed building.
Lay 25–40 mm of sharp sand and screed it flat with a length of straight timber. This is your levelling layer.
Work from one corner with 600×600 mm slabs, joints tight. Tap each one down with the rubber mallet and check level constantly — across, along, and corner to corner.
Brush kiln-dried sand into the joints and leave it 24–48 hours before building. Stand back: that's a proper base.
The sub-base is non-negotiable. Slabs laid straight on soil will move. A cheap 100 mm layer of compacted type-1 is the difference between a base that's level in five years and one that's a rocking, weed-strewn mess by next spring.
The most common question — and the most common mistake.
Never put a shed straight onto grass. Grass holds moisture against the timber floor, the ground is never truly level, and the shed slowly sinks and rots. It feels like a shortcut; it's the most expensive mistake you can make.
To build on a grassed area properly, you treat the grass as something to remove, not build on:
Cut and lift the turf across the footprint plus a margin. Compost it or relay it elsewhere.
Excavate ~150 mm and compact 100 mm of MOT type-1, exactly as for a slab base. The hardcore stops grass and weeds returning and gives you drainage.
Then either bed paving slabs on sharp sand, or sit a treated-timber base frame on the compacted gravel — both keep the shed floor up off the damp ground.
If you genuinely can't dig (tree roots, rented garden), the next-best no-dig option is a treated-timber base on gravel boards and a weed membrane, levelled with packers — but a proper sub-base will always outlast it.
If you're building a workshop, a garden office, or anything over about 10×8ft, concrete is worth the extra effort. It's permanent, dead level, and carries heavy loads without flexing.
The headlines: timber shuttering set perfectly level, 100 mm of compacted type-1, a 1000-gauge damp-proof membrane (non-negotiable — it stops ground moisture wicking up), then a C20 (GEN3) concrete mix poured 100 mm thick, screeded and floated, and cured under polythene for at least three days. For anything bigger than about 0.3 m³, order ready-mix rather than bagging it by hand.
We've got the full concrete-slab method — formwork, DPM, mix, pour and cure — in the Foundation step of the build guide. Start there if concrete's your plan.
Match the base to your shed's actual footprint, which is usually a little under the nominal size.
Get the exact dimensions: the free 8×6 shed plan (PDF) includes the precise base size, plus the full cut list and build sequence. Download it before you order materials.
Rough DIY material costs for an 8×6 base (2026, ex-tool-hire):
| Base type | Materials (8×6) | Effort |
|---|---|---|
| Paving slabs on type-1 | £60–120 | A weekend |
| Concrete slab | £120–250 | A weekend + curing |
| Timber base on gravel | £70–140 | A day |
| Plastic grid + gravel | £80–160 | A few hours |
Add ~£30–60 for a day's plate-compactor hire for the slab and concrete methods. Prices vary by region and supplier; check the materials list for what to buy.
For most garden sheds, paving slabs on a compacted MOT type-1 sub-base — best balance of cost, durability and effort. Concrete for workshops and big sheds; timber-on-gravel for sloping or soft ground.
Yes, if the patio is solid, level and free-draining you can sit the shed on it. Just don't build onto bare soil or grass.
100 mm (4 inches) minimum on a compacted sub-base. Go 150 mm with A142 mesh for heavy workshop machinery.
Under a concrete slab, yes — always. A 1000-gauge DPM stops ground moisture rising into the slab and your shed. For a slab base, the gap under the timber floor does the same job.
A slab base: 24–48 hours to settle. A concrete slab: about 7 days before you build gently on it, full strength at 28 days.
Download the free 8×6 plan — dimensioned drawings, cut list and build sequence — then start building.