How to Price Decking: UK Labour & Materials Guide 2024

Quick Answer: A UK decking installation prices at £80-£140/m² for treated softwood (typical pine/spruce) on a standard joist sub-frame, £140-£220/m² for hardwood (oak, ipe, balau) on a treated softwood sub-frame, and £180-£280/m² for composite decking on aluminium sub-frame. A typical 20m² decking installation prices at £1,800-£4,500 inclusive of foundations, sub-frame, deck boards, and finishing. Decking above 300mm from ground level may need planning permission; structural decking on slopes or large areas may need Building Regulations approval.

Summary

Decking is the most popular garden hard-landscaping addition in UK domestic gardens after patios. The visual appeal is significant — a deck transforms an unused garden corner into usable outdoor living space. The pricing variability mirrors patios: a cowboy bolts decking on 6-inch timber bearers directly onto soil for £30/m²; a proper installer specifies concrete pad foundations, treated bearers on damp-proof spacers, and weatherproof fixings for £100-£200/m².

Material choice drives the major price tier. Treated softwood is the volume choice (£15-£25/m² supply for the deck boards), hardwood is the premium choice (£45-£95/m² supply), and composite is the maintenance-free contemporary option (£55-£130/m² supply). The sub-frame matters even more than the boards — a properly-built treated softwood sub-frame should last as long as the boards (typically 15-25 years for softwood, 25-40 years for hardwood, 25-40 years for composite).

This guide covers all three material categories with sub-frame design, foundations, balustrading, and lighting. For patios see patio installation pricing guide; for fencing see fencing installation pricing guide.

Key Facts

Materials (supplied)

Labour and ancillary costs

Regulatory

Quick Reference Table

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Deck Type Spec Size Days Total Range (Regional) Total Range (London)
Budget softwood Treated pine, basic frame 10m² 2-3 £900-£1,600 £1,100-£1,900
Standard softwood Treated pine, concrete pads 20m² 3-5 £1,800-£3,500 £2,200-£4,200
Premium softwood Kiln-dried, balustrading 20m² 4-6 £2,500-£4,200 £3,000-£5,000
Hardwood (oak) Hardwood on softwood frame 20m² 5-7 £3,500-£5,800 £4,200-£6,800
Hardwood (ipe/iroko) Premium hardwood 20m² 5-7 £4,200-£6,800 £5,000-£8,000
Composite (basic) Composite on softwood frame 20m² 4-6 £3,200-£5,200 £3,800-£6,200
Composite (premium) Capped composite, aluminium frame 20m² 5-7 £4,500-£7,500 £5,500-£8,800
Large multi-level deck Hardwood, balustrading, steps 40m²+ 8-12 £8,500-£14,500 £10,000-£17,000

Add £55-£140/linear metre for balustrading, £55-£140 per step, £120-£280 for lighting (LED strip + transformer).

Detailed Guidance

Material choice — softwood, hardwood, composite

Treated softwood is the volume choice. Pressure-treated pine or spruce (UC4 use class for ground contact, UC3 for above-ground) at £15-£25/m² supplied. Lifespan 10-15 years with annual oil/stain maintenance; 15-25 years for premium kiln-dried treated softwood.

Pros: cheapest, easy to cut and fit, takes oil/stain well. Cons: needs annual maintenance, prone to splinter and warp, fades in 2-3 years.

Hardwood is the premium natural choice. Oak (UK-sourced) at £55-£95/m², ipe/iroko/balau (imported tropical hardwoods) at £65-£120/m². Lifespan 25-40 years, often outlives the sub-frame. Density makes hardwoods harder to cut and fix — predrilling is essential, stainless screws mandatory (carbon screws corrode in contact with tannin).

Pros: distinctive natural appearance, very long lifespan, weather-resistant. Cons: highest cost, FSC-certification of imported hardwoods variable, harder to work with.

Composite decking is the contemporary maintenance-free option. WPC (wood-plastic composite, typically 60% wood fibre + 40% HDPE plastic) or capped composite (polymer cap over WPC core for stain resistance). Lifespan 25-40 years. UV-stable colours.

Pros: zero annual maintenance, no splintering, slip-resistant ridges available, consistent appearance. Cons: higher upfront cost, looks artificial to some customers, more thermal expansion than timber.

Sub-frame design — the load-bearing element

The sub-frame is the structural component. Designed correctly, it should outlast the boards. Standard spec for a domestic deck (light pedestrian loading, max 1.5kN/m²):

For decks attached to the house, the ledger board (the joist fixed to the house wall) is the structural critical element. Must be properly waterproofed (flashing above), positively fixed (not just nailed), and well below DPC level. Many failures are at the ledger interface.

For freestanding decks, support posts (100x100mm treated softwood or galvanised steel) on concrete footings provide the foundation. Post depth: 600-900mm below ground level for stability.

Composite decking — special considerations

Composite decking is the fastest-growing UK market segment. Specific install considerations:

  1. Thermal expansion — composites expand more than timber. Specify 5-8mm gaps between board ends, 3-5mm gaps between boards and adjoining walls/posts.
  2. Hidden fixings — most composite systems use hidden clips on the underside, not visible screws. Adds labour time (slower than screwing through the face) but cleaner finish.
  3. Joist spacing — 300-350mm centres for most composites, vs 400-450mm for softwood. More joists = more sub-frame cost.
  4. Aluminium sub-frame option — premium composite installations (Millboard, Trex) often use aluminium sub-frame for matched expansion behaviour. £35-£65/m² premium over treated softwood.
  5. Slip resistance — most composites are BS 7976 R10 or R11 rated dry; some grades drop below R9 wet. Specify R11 minimum for any wet-area decking.

Balustrading, steps, and lighting

Balustrading is required by Building Regulations Part K for decks more than 600mm above ground level. Domestic standard: 1100mm high, no climbable horizontal elements between 100mm and 600mm (the "100mm ball gap" rule).

Balustrade options:

Steps from deck to ground are usually 180-200mm risers, 280mm treads. Per linear metre of step run: £55-£140 supply + labour.

Lighting: LED strip lights under-step or post-mounted are the volume add-on. £120-£280 supply + 1-2 hours sparks time. Always low voltage (12V or 24V) for outdoor compliance.

Maintenance and lifespan

Softwood maintenance — annual clean (pressure wash on low setting), annual oil/stain re-coat. Decking oil products: Osmo Decking Oil (£25-£45/L), Liberon Decking Oil, Ronseal. Cost: £60-£150/year materials + 0.5-1 day labour if professional.

Hardwood maintenance — annual clean only (no oil needed for most hardwoods). Light oil every 2-3 years if customer wants to retain colour rather than letting it silver naturally. Cost: £40-£100/year.

Composite maintenance — semi-annual clean (mild detergent and brush). No oiling required. Lifespan claim 25-40 years.

Hidden costs and risk premium

The five most-missed cost lines in decking quotes are: (1) ground preparation — if the area is sloping or has poor drainage, foundation work scales up significantly; (2) ledger waterproofing — flashing details if attached to brick or render wall (£80-£180); (3) handrail / balustrade height check if customer chose low decks then changes mind to elevated; (4) tree root or stump removal under foundation positions; (5) waste disposal — old decking removal often hides damaged garden underneath.

Risk premium of 10-15% is standard on existing-deck replacement jobs (unknown sub-frame condition). Premium of 15-25% on sloping gardens or multi-level decks.

Frequently Asked Questions

Do I need planning permission for a deck?

Most domestic decks fall within Permitted Development if: (1) less than 300mm above ground level, (2) less than 50% of garden area, (3) not in a conservation area or listed building, (4) not in front of the principal elevation. Decks above 300mm typically need planning permission, particularly in semi-detached and terraced properties where neighbours may overlook. Always check with the local planning department for marginal cases.

How long does softwood decking last?

Pressure-treated softwood decking, properly installed with adequate ventilation and annual oil/stain maintenance, lasts 10-15 years. Premium kiln-dried treated softwood lasts 15-25 years. Key longevity factors: ventilation below the deck (water and air must move freely), positive drainage (no ponding), and annual coating. Failure modes are rot (insufficient ventilation), splitting (UV damage without coating), and warping (kiln-drying defect).

Is composite decking really maintenance-free?

Largely yes — but not fully maintenance-zero. Composite decking needs occasional cleaning (semi-annual mild detergent brush) and benefits from a 5-yearly inspection of hidden clips and fixings. The "no annual oil" is real; oil/stain on composite degrades the surface cap. Mineral-stain removal (red wine, BBQ grease) may need specialist composite cleaners. Total maintenance cost ~£15-£35/year for typical 20m² deck.

Can I attach decking directly to the house wall?

Yes, using a ledger board (47x150mm treated, fixed with M10 anchor bolts or coach screws). Critical details: (1) ledger MUST sit below DPC level OR have an integral waterproof flashing above; (2) ledger must be on damp-proof spacers (not direct contact with wall); (3) ledger fixings must penetrate the brick/blockwork solidly. Improperly-flashed ledgers cause house wall damage within 2-5 years and are the most common decking failure.

What's the cost difference between deck boards and the sub-frame?

For a typical softwood deck: deck boards 30-40% of materials, sub-frame 30-40%, foundations 15-25%, fixings/finishing 10-15%. For premium hardwood or composite: deck boards rise to 60-75% of materials, sub-frame remains 15-25%. The sub-frame cost is relatively stable across material tiers — the variable is the board cost.

Regulations & Standards