Decking Project Estimator
Complete decking shopping list — surface boards, joists, bearers, posts and all fixings in one estimate. Covers softwood, hardwood and composite. 2026 UK pricing.
Enter the finished deck surface height above ground. Over 300mm requires planning permission.
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Build Guide
How to Build a Deck
Posts and bearers
100×100mm pressure-treated posts set 600mm into the ground with Postcrete, spaced at 1.5m maximum centres along bearer lines. Bearers (typically 150×47mm) span between posts at right angles to the joists. Notch the top of each post or use proprietary post brackets. Keep all timber at least 50mm clear of soil contact.
Joists and sub-frame
100×47mm joists at 400mm centres for softwood and hardwood; 300mm centres for composite. Fix to bearers using joist hangers (not skew nailing — hangers give a stronger, more consistent connection). Add noggins between joists at the mid-span and around any perimeter where boards need edge support. All sub-frame timber must be C16 or C24 pressure treated.
Surface boards and fixings
Maintain consistent gaps: 5mm softwood, 6mm hardwood, 8mm composite. Use 65–75mm stainless or hot-dip galvanised screws — 2 per crossing per joist. For hardwood, pre-drill and countersink. For composite, use the manufacturer's hidden clip fixing system — surface screwing composite boards voids most warranties and causes visible cracking.
Always lay boards bark-side up (growth rings curving upward on the end grain) — this causes boards to cup away from the surface rather than toward it, shedding water better and reducing the trip hazard from cupped edges.
FAQ
Common Questions
400mm centres for standard treated softwood boards (25–32mm). 300mm for composite (always check manufacturer spec). 400mm is the safe standard — closer spacing adds cost and material but reduces bounce. Never exceed 600mm centres for any domestic decking application.
Decking under 300mm above ground generally falls under Permitted Development in England. Over 300mm at any point requires planning permission. Total outbuildings plus decking must not exceed 50% of the garden. Conservation Areas and listed buildings have stricter rules. Always check with your local planning authority before starting.
Pressure-treated softwood: 15–25 years with regular oiling/staining. Hardwood (bangkirai/ipe): 25–40 years. Composite: 25–30 years (typically with a manufacturer warranty). Sub-frame timber often fails before the boards — use the highest treatment class (UC4 or UC3) for any posts in or near ground contact.
65–75mm × 4mm stainless steel A4 grade or hot-dip galvanised. Never use zinc-plated screws with hardwood — tannins cause black staining. Two screws per board per joist crossing. Pre-drill hardwood to prevent splitting. For composite, use the manufacturer's clip or screw system — surface screwing may void the warranty.