Decking Calculator
Calculate the number of decking boards and fixings needed for any size deck — plus estimated material costs. Works for timber and composite decking.
Decking Build Guide
Choosing Decking Material
Softwood (pressure-treated pine): £15–25 per m2 for boards. Affordable, widely available, needs annual oiling or staining to prevent weathering. Hardwood (Ipe, Balau, Bangkirai): £40–80 per m2. Extremely durable (25+ years), beautiful finish, but expensive and requires careful sourcing for sustainable certification. Composite (Trex, Millboard, Eva-Last): £40–100 per m2. Low maintenance, resistant to rot and splinters, but more expensive upfront.
Structure and Frame
The frame (joists and posts) typically costs as much as the boards themselves. Allow for deck posts every 1.5–2m, concrete post bases, 47x100mm joists at 400mm centres for most boards, and a rim joist around the perimeter. For a 4x3m deck, expect 8–10 posts, 7–9 joists at 4m, and 3 rim joists. Use pressure-treated timber throughout — untreated timber in ground contact will rot within 3–5 years.
Planning Permission
In England, a deck is permitted development (no planning permission needed) if it is under 30cm above ground level, within the permitted area (no more than 50% of garden), and not in front of the house. Decking over 30cm high requires planning permission. In conservation areas and listed buildings, additional restrictions apply. Scotland, Wales, and Northern Ireland have slightly different rules.
DIY vs Professional Installation
A professional builder charges £100–150 per day. A 4x3m deck takes 2–3 days for an experienced builder — labour cost £200–450. DIY is achievable with basic carpentry skills and the right tools (circular saw, drill, post hole digger). Allow 2–3 weekends for a first build. DIY saves 40–60% of total cost.
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