Garden Shed — Material & Cost Calculator
Calculate materials needed and estimated cost for a garden shed or timber outbuilding, including base, cladding, and roofing.
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Garden Shed Guide
Permitted Development — When Do You Need Planning?
In England, most garden sheds are permitted development (no planning permission needed) if: single storey only. Maximum height: 2.5m within 2m of a boundary. Maximum height: 4m for a dual-pitched roof OR 3m for any other roof, if more than 2m from boundary. Does not extend beyond the side of the house (outbuilding only, not side extension). Permitted development does NOT apply: on listed buildings or in conservation areas (always check). To buildings forward of the principal elevation of the house facing a road, which generally do need planning permission regardless of size.
What's the key thing to understand about Base Construction?
Concrete slab: most durable. Depth: 100mm minimum (150mm for larger sheds). Mix: 1 part cement : 2 parts sharp sand : 3 parts 20mm aggregate. Or use C25 ready-mix for larger pours. Reinforcement: A142 mesh for larger slabs. Paving slabs on hardcore: 50mm MOT Type 1 hardcore, compacted. Then 25mm sand bed. Then slabs. Adequate drainage essential — do not trap water under the shed. Timber bearers: 100×75mm treated timber on 100mm shingle/gravel. Allows ventilation under floor — prevents rot. Cheapest base option for a small, lightweight shed, though less durable long-term than a concrete slab.
What do I need to know about Timber Specification?
Framing: C16 grade treated timber (47×100mm or 47×75mm studs at 600mm centres). Cladding thickness: minimum 12mm for shiplap. 16mm for better insulation and rigidity. Roof: OSB/3 18mm minimum for roof decking. Then 3G underlay felt. Then mineral surface felt strips. Or corrugated bitumen/metal roofing. Treating timber: all structural timber should be pressure-treated for in-ground or near-ground use. External cladding: paint or stain annually with exterior-grade wood preserver. Floor: 12mm exterior-grade plywood or OSB is the minimum sensible thickness to avoid flexing and sagging under weight over time.
What do I need to know about Cost Estimates?
DIY timber shed costs (2024): small shed (1.8×2.4m): materials £300-600. Medium shed (2.4×3.0m): materials £600-1,200. Large shed/workshop (3×5m): materials £1,500-3,000. Supply-only flat pack shed (similar sizes): £300-800 (thin cladding, limited lifespan). Purpose-built quality shed: £1,200-3,500 erected. Insulating for year-round use: add 50mm mineral wool between studs + vapour barrier + internal lining board. Additional £300-600 for insulation. Key trade-off: a quality DIY build with 16mm cladding and a proper base costs more upfront than a cheap flat-pack shed, but lasts significantly longer and needs far less maintenance.