Shed Base Project Estimator UK

A shed base requires either a 75-100mm concrete slab or a timber frame with gravel/sub-base. For 2026 professional installs, factor in 100mm of Type 1 sub-base and a DPM (Damp Proof Membrane). This estimator calculates the concrete volume or timber components plus the necessary excavation waste.

Base Dimensions & Specs

Engineering Specifications

75mm (Small Shed) 100mm (Standard) 150mm (Workshop)
50mm (Firm Soil) 100mm (Standard) 150mm (Soft Ground)

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Total Sub-Base Area: 0 m²
Estimated Total Material Cost: £0
(Based on UK trade averages for MOT, Timber, DPM, and Concrete materials)
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How to Build a Shed Base

A solid foundation is vital to prevent your shed from warping, rotting, or sinking. A concrete base is the gold standard for durability.

1. Excavation & Sub-Base

Mark out the area and dig to a depth of roughly 200mm. Fill the first 100mm with MOT Type 1 and compact it thoroughly with a wacker plate. This foundation provides the structural support and drainage needed.

2. Formwork & Membrane

Build a timber frame (shuttering) using treated timber to hold the concrete. Line the inside with a Damp Proof Membrane (DPM). This prevents moisture from the ground soaking into the concrete and eventually rotting your shed floor.

3. The Concrete Pour

Fill the frame with a C20 concrete mix. For most sheds, a 100mm thickness is ideal. Use a straight timber board to 'tamp' the concrete level with the top of your frame, ensuring a perfectly flat surface for your shed to sit on.

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UK Building Regulations: Sheds & Outbuildings

Building a shed base usually falls under "Permitted Development", but the size and position of the building must comply with UK rules:

  • Boundary Proximity: If the outbuilding is within 2 metres of a property boundary, the total height of the building must not exceed 2.5 metres.
  • Garden Coverage: Outbuildings and other extensions must not cover more than 50% of the total area of land around the original house.
  • Use: These rules only apply to non-habitable outbuildings (sheds, greenhouses, garages). Habitable spaces require full building regulations approval.
  • Single Storey: Outbuildings must be single-storey with a maximum eaves height of 2.5 metres.
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Frequently Asked Questions

Should a shed base be bigger than the shed?

Technically, the base can be the exact size of the shed. However, professionals often make the base 50mm larger on all sides to allow for slight overhangs and better drainage away from the timber.

What concrete mix is best for a shed base?

A standard C20 mix (1 part cement, 2 parts sand, 3 parts aggregate) or a 1:4 mix of cement and combined ballast is perfect for shed foundations.