How much concrete do I need for a shed base?

For a standard 8x6ft (2.4x1.8m) shed, you need approximately 0.43 cubic metres of concrete at 100mm depth. This equates to about 17 bags of 25kg ready-mix concrete. For larger sheds or heavy-use buildings, increase the depth to 150mm.

How deep should a shed base be?

A concrete shed base should be 75-100mm (3-4 inches) deep for a standard garden shed, plus a 50-75mm compacted sub-base of MOT Type 1 or gravel underneath. For heavier structures like workshops or log cabins, increase the concrete depth to 150mm (6 inches).

Do I need planning permission for a shed base?

No planning permission is needed for a shed base under Permitted Development rights, provided the shed is single storey, no more than 3m high (or 4m for dual-pitched), no more than 2.5m high if within 2m of a boundary, and covers no more than 50% of the garden. Listed buildings and conservation areas may have additional restrictions.

Is a concrete base or paving slab base better for a shed?

Paving slabs are easier for DIY, cheaper, and provide good drainage. They work well for standard garden sheds up to 10x8ft. Concrete bases are stronger, last longer, and are better for large sheds, workshops, or heavy equipment. Concrete is the preferred choice for any shed over 10x8ft or on soft/sloping ground.

Shed Base Calculator — Concrete & Gravel Needed (UK)

Complete Guide to Shed Bases in the UK

A solid base is the single most important factor in the longevity of your garden shed. Without a proper base, the shed will settle unevenly, doors and windows will jam, the floor will sag, and damp will rot the timbers from below. A well-built base costs a fraction of the shed price but can double its lifespan.

Types of Shed Base

Base Type	Cost (8x6ft)	DIY Difficulty	Best For	Lifespan
Concrete slab	£120-£200	Moderate	Large sheds, workshops, log cabins	50+ years
Paving slabs	£80-£150	Easy	Standard garden sheds up to 10x8ft	20+ years
Gravel pad (eco grid)	£60-£120	Easy	Standard sheds, good drainage	15-20 years
Timber frame (bearers)	£40-£80	Easy	Small sheds on flat ground	10-15 years
Concrete blocks/pads	£30-£60	Very Easy	Small sheds, temporary placement	20+ years

Concrete Shed Base

A concrete slab is the strongest and most durable option. It creates a perfectly flat, rigid surface that will never move or settle. For a standard garden shed, a 100mm (4-inch) concrete slab on a 75mm compacted sub-base is ideal. For workshops, log cabins, or any structure where you will be storing heavy items, increase the concrete to 150mm.

How to build a concrete shed base:

Mark out the area — Use string lines and pegs. Make the base 100-150mm larger than the shed on all sides
Excavate — Dig out to 175mm depth (75mm sub-base + 100mm concrete). Ensure the bottom is level and firm
Build formwork — Use 100mm x 25mm timber boards held in place with pegs. Check levels with a spirit level
Lay sub-base — Spread 75mm of MOT Type 1 or compacted hardcore. Compact with a plate compactor or hand tamper
Add membrane — Lay a damp-proof membrane (DPM) over the sub-base to prevent moisture rising
Pour concrete — Use C20 mix (1:2:4 ratio) or ready-mix. Pour, spread with a rake, and level with a straight edge (screed board). Tamp down to remove air pockets
Cure — Keep the concrete damp for at least 3 days. Do not place the shed for at least 7 days (28 days for full strength)

Paving Slab Base

Paving slabs are the most popular DIY shed base option. Standard 600x600mm or 450x450mm slabs are laid on a compacted sand and sub-base bed. The slabs should be level, stable, and have minimal gaps between them.

For an 8x6ft shed, you need 12 paving slabs (600x600mm) arranged in a 4x3 grid. Lay them on 25-30mm of sharp sand over a 50-75mm compacted sub-base. Check each slab is level with its neighbours using a spirit level.

Gravel Pad Base

A gravel pad with plastic eco grid provides excellent drainage and is easy to install. Excavate 100-150mm, lay a weed membrane, install the eco grid frames, and fill with 20mm gravel. The grids prevent the gravel from spreading and create a stable, porous surface. This method is popular because it requires no mixing, curing, or heavy lifting.

UK Planning Rules for Sheds

Permitted Development (no planning permission needed) if all conditions met:

Single storey with no internal room above ground level
Maximum 3m height (flat roof) or 4m (dual-pitched) for detached buildings
Maximum 2.5m height if within 2m of any boundary
Does not cover more than 50% of the garden area
Not in front of the principal elevation of the house
Not on designated land (conservation area, AONB, National Park) without checking

How Much Concrete for Common Shed Sizes

Shed Size	Base Size (with overhang)	Concrete (100mm)	25kg Bags	Sub-base (75mm)
6x4ft	2.1 x 1.5m	0.32 m³	13 bags	0.24 m³
8x6ft	2.7 x 2.1m	0.57 m³	23 bags	0.43 m³
10x6ft	3.3 x 2.1m	0.69 m³	28 bags	0.52 m³
10x8ft	3.3 x 2.7m	0.89 m³	36 bags	0.67 m³
12x8ft	3.9 x 2.7m	1.05 m³	42 bags	0.79 m³
12x10ft	3.9 x 3.3m	1.29 m³	52 bags	0.97 m³

For concrete volumes above 1 m³, consider ordering ready-mix concrete delivered by truck. It is often cheaper and far less labour-intensive than mixing by hand.

Where to Buy Materials

Ready-mix concrete bags are available from B&Q, Wickes, Screwfix, and Jewson. For volumes over 1m³, a volumetric mixer delivery from companies like Hanson, Breedon, or local plants is more cost-effective (typically £100-£150/m³ delivered). MOT Type 1 sub-base is available from builders' merchants by the bulk bag (850kg, approximately 0.5m³).

Shed Base Calculator — Concrete, Gravel & Paving Slabs