outdoor
Decking and garden carpentry
Decking is a raised timber or composite platform, and the frame under it decides how long it lasts. Expect £60 to £110 per square metre supplied and fitted, with composite at the top of that range and softwood at the bottom.
What it costs. Decking costs £60 to £110 per square metre supplied and fitted. Full cost breakdown for decking.
What the job covers
- Timber and composite decking
- Raised decks and steps
- Balustrades and handrails
- Sub-frame repair and re-boarding
- Pergolas and screening
What is involved
The sub-frame is the job. Joists at 400mm centres for timber boards, or 300mm for most composite, on treated bearers with a clear gap to the ground so air moves underneath. Ground contact is what kills decks: a bearer sitting on soil holds water against the timber year round. Where the deck meets the house it must stay at least 150mm below the damp proof course, and it must not bridge the airbricks.
Boards are the visible choice. Softwood is cheapest and needs cleaning and re-treating every year or two. Hardwood lasts longer, moves less and costs considerably more. Composite does not rot or need oiling, but it expands lengthways with heat, so the fitter has to leave the manufacturer's gaps at the ends or it buckles in summer. Every board type gets slippery in shade and needs cleaning.
Choosing someone for the job
Ask what the joist spacing will be and check it against the board manufacturer's requirement. Ask how the frame is kept off the ground. Ask what the fall is: a deck should shed water away from the house, not hold it.
Common questions
Do I need planning permission for decking?
Usually not if it is under 300mm above ground and the total garden coverage stays within permitted development. Raised decking and balustrades over that height can need permission and can raise overlooking issues.
How long does a deck last?
Ten to fifteen years for treated softwood if the frame stays dry, twenty-five or more for hardwood and composite. The frame nearly always outlives or kills the boards.
Composite or timber?
Composite for low maintenance and stable colour; timber for lower cost and for a look that weathers. Composite needs wider expansion gaps and closer joist spacing.
Can decking go over an existing patio?
Yes, and it is a good base, provided there is still ventilation under the boards and the finished height stays clear of the damp proof course.