Shed Base Calculator

Your gravel base should extend at least 150mm (6 inches) beyond the shed footprint on all sides. This overhang ensures the shed sits entirely on the base, provides space for rainwater to drip clear of the structure, and makes positioning the shed easier. For larger sheds (10×8 or bigger), some installers recommend a 200–300mm overhang for extra stability.

A standard gravel shed base uses two layers: 100mm of compacted MOT Type 1 sub-base (order 125mm loose to allow for 25% compaction) plus 50mm of decorative surface gravel on top. This gives a total finished depth of about 150mm — more than enough for sheds up to around 12×10ft. For very large or workshop-type buildings, increase the sub-base to 150mm compacted.

Gravel bases are cheaper, faster to build, require no curing time, and provide excellent natural drainage. A concrete base can trap moisture underneath the shed, leading to damp and rot in the timber floor. Gravel allows air to circulate beneath the building and water to drain freely. Gravel bases also don't crack with ground movement and can be easily adjusted or removed if you ever relocate the shed.

Use MOT Type 1 (crushed limestone 0–40mm) for the sub-base layer — it compacts into a solid, load-bearing platform. For the surface layer, 20mm gravel such as golden gravel, grey granite, or limestone chippings works well. Avoid pea gravel or rounded stones for the surface as they shift too easily under the weight of the shed.

Yes — lay a heavy-duty weed membrane on the bare ground before adding the sub-base. This prevents weeds growing up through the gravel and stops the sub-base mixing into soft soil beneath. Use a minimum 100gsm geotextile membrane and overlap any joins by at least 150mm.

You can place a shed directly onto a well-prepared gravel base, but using pressure-treated timber bearers between the shed floor and the gravel is highly recommended. Bearers (typically 75mm × 50mm or 100mm × 50mm treated timber) lift the shed off the surface, improving air circulation and preventing moisture damage to the floor. Space them at 400mm centres running the width of the shed.

For a standard 8×6ft shed, you'll need approximately 0.7 tonnes of MOT Type 1 and 0.25 tonnes of surface gravel — costing roughly £35–£55 in materials depending on your supplier. Add another £20–£30 for weed membrane. This is typically a third of the cost of a concrete pad and can be completed in a single afternoon.

Yes — the ground should be roughly levelled before you start. Remove turf and topsoil to a depth of about 150–200mm, creating a shallow excavation. For sloped sites, you may need to cut into the uphill side and build up the downhill side. Use a spirit level across the excavation before adding sub-base, and compact the soil at the bottom to prevent future settling.