structures
Decking installation
£40 to £73 per square metre buys softwood decking installed in 2026 and £62 to £110 buys hardwood. Twenty five square metres of softwood totals £1,000 to £1,850, while labour on its own accounts for £22 to £55 per square metre.
What this covers
What it costs. £2,600 is the average 30 square metre timber deck in 2026. Full cost breakdown.
What the job covers
- Ground preparation and a levelled frame
- Softwood and hardwood boards
- Balustrades, steps and fascias
- Ventilation and drainage under the deck
- Treating and maintaining an existing deck
What is involved
Boards are the cheap part. Beneath them sits a joist frame that decides whether the deck still feels solid in year five, and joist centres are the number to ask about: 400mm for standard boards laid square, tightening to 300mm where boards run diagonally. Bearers rest on concrete pads or paving slabs rather than soil, with a damp proof membrane between timber and concrete. Ground clearance of at least 100mm keeps air moving underneath, and a frame built tight to the earth traps moisture and rots from below.
Decks against a house need care around the damp proof course. The walking surface stays at least 150mm below it, and where that forces the deck down, a step is the right answer rather than bridging the membrane. Ledger boards bolted to a wall get spaced off it so water drains behind rather than sitting against render. Falls of roughly 1 in 100 across the boards, or a 5mm to 8mm gap between them, shed rain; boards butted tight hold water and cup.
Groundwork beneath a deck is not optional. Turf and topsoil come off, a weed membrane goes down, and 50mm of gravel over it stops growth and helps the ground drain. Pads get set level to one another and the frame packed with shims, because a frame propped on offcuts moves. Softwood decking arrives pressure treated, but every cut end is raw timber and wants end grain preservative. Anti-slip inserts or a grooved profile earn their keep on north facing decks, where algae builds through winter and smooth timber turns dangerous.
Choosing someone for the job
Joist centres: ask the spacing, 400mm for standard boards laid square. Clearance: ask how far the frame sits above ground and what the bearers rest on. Damp proof course: ask how far below it the walking surface lands. Fixings: ask whether stainless or coated screws are going in. Cut ends: ask whether end grain preservative is applied to every cut.
Common questions
How long does a timber deck last?
Fifteen to twenty years for pressure treated softwood on a frame built clear of the ground and washed down annually. Hardwood runs longer. The frame usually outlives the boards, so decks failing early almost always had bearers sitting straight on soil.
Does decking need planning permission?
Usually not, provided the platform is no more than 30cm above ground level, sits behind the principal elevation, and together with other extensions covers no more than half the garden. Raised decks overlooking neighbours can need permission. Listed buildings and designated land such as National Parks and conservation areas follow separate rules.