Decking Cost UK: Timber vs Composite Prices That Add Up

Last updated: 17 August 2026 · By Mossy Tariq, Founder — Property Blueprint Co.

Two quotes for the same deck, same size, same boards, can come back £1,800 apart, and the difference is almost never the timber you can see. It is the structure underneath it — how the joists are spaced, what the posts sit on, and how the ground was prepared before anything was built.

That is the thing to understand before comparing a single decking cost: the visible surface is roughly half the job, and it is the half that both quotes describe honestly. The other half is invisible on the day the deck is finished and decisive five winters later, which makes it the easiest place in the whole project to cut a price without the buyer noticing.

The figures below are indicative UK market ranges for 2026, drawn from current UK supplier and installer pricing. They are a planning baseline to measure a quote against, not a quote.

Half of what a deck costs is under it.
Price the sub-frame, and the quotes
stop looking mysterious.

What follows separates supply from installed pricing, puts a real number on the structure below the boards, settles the timber-versus-composite question over a ten-year horizon rather than a purchase price, and sets out the two approval thresholds a raised deck crosses in England.

What does decking cost per square metre in the UK in 2026

There are two numbers in circulation and they are frequently confused, which is why online figures look irreconcilable.

Supply only — the boards on their own. Pressure-treated softwood timber decking commonly runs £20 to £45 per square metre. Composite boards run £37 to £92 per square metre, split roughly into entry-level uncapped hollow boards from around £37, mid-range wood-grain boards from around £42, and capped solid boards from around £54.

Fully installed — boards, sub-frame, fixings, ground preparation and labour. Timber typically lands at £40 to £108 per square metre and composite at £80 to £200, with mid-range composite projects most commonly £90 to £135. Raised decks, difficult access, premium board grades and integrated steps or balustrade push the installed figure to £150 to £350 per square metre. Regionally, the North West, Yorkshire and the Midlands sit at the lower end of each band and London and the South East at the upper end.

The gap between the two numbers is the whole argument of this article. On a mid-range composite deck, boards account for roughly a third to a half of the installed price. Everything else is structure, groundwork and days on site — and that is precisely the part a cheap quote quietly reduces.

Why the sub-frame is the half of the quote nobody sees

A deck is a suspended floor built outdoors. The boards are the finish; the joists, bearers, posts and footings are the building.

The quantities explain the cost. A timber sub-frame needs roughly seven linear metres of joist for every square metre of finished deck, at around £17 per square metre in treated timber alone, before posts, footings, fixings, weed membrane and the labour to set it all true. On a twenty square metre deck that is 140 metres of timber to cut, level and fix, which is where the days go.

Three shortcuts turn up repeatedly in cheap quotes, and all three are invisible at handover. Joists set at wider centres than the board manufacturer specifies, which produces bounce in year one and a sagging line by year three. Posts founded on paving slabs or a shallow bed rather than concrete footings, which moves as the ground does. And no ventilated void or weed membrane beneath, which traps moisture against the underside of the boards and rots a deck from below no matter what treatment class the timber carries.

There is a specific trap for anyone re-boarding an existing deck. Composite boards generally require closer joist centres than softwood, so a sub-frame built correctly for timber is not automatically suitable for a composite upgrade. A quote that prices new composite boards onto an old frame without stating the centres is pricing a deck that will move.

Timber or composite over a ten-year horizon

The purchase price says timber. The ten-year cost usually says composite, and the reason is labour rather than material.

Softwood decking carries a low capital cost and a real recurring one. Cleaning and re-treating is roughly a day's work and a tin of treatment every year, and boards in a shaded or north-facing garden reach the end of their service life sooner than the same boards in an open, well-drained one. Replacement typically comes round well inside the life of a capped composite board.

Composite reverses the profile: a higher capital cost, then washing rather than treating. It is not maintenance-free — the phrase is a marketing claim rather than a specification — but the annual commitment is a hose and a brush rather than a day and a purchase.

So the honest decision rule is about how long you intend to own the outcome. Under about five years, timber usually wins on total spend. Beyond ten, composite usually does, and the crossover moves earlier the more shade and rainfall the deck sits under. Where the deck is one element of a wider outdoor project, the sequencing and budget interactions are covered in the UK outdoor project cost breakdown.

When does a deck need planning permission or Building Regulations approval

Two separate thresholds apply in England, and they are commonly confused with one another.

Planning. Under the Planning Portal, decking is permitted development where the decking is no more than 30 centimetres above the ground, and where the decking or platforms, together with other extensions and outbuildings, cover no more than 50 percent of the garden area. Cross either line and an application is required. Listed buildings, conservation areas and Article 4 directions remove those freedoms, and Scotland, Wales and Northern Ireland run separate planning systems with their own thresholds.

Building Regulations. The Planning Portal's position is that Building Regulations should be assumed to apply to every deck structure requiring planning permission. In practice the requirement that bites on a raised deck is guarding: Approved Document K expects pedestrian guarding in dwellings wherever someone could be injured falling more than 600 millimetres, and its Table 3.1 sets the height for external balconies and the edges of external floors in single-family dwellings at 1,100 millimetres, against 900 millimetres for internal stairs and landings. Confirm the position for your deck with local authority building control before it is built rather than after.

One practitioner note that catches people out: the 30 centimetre measurement is taken to the deck surface, and gardens are rarely level. A deck built to a single horizontal plane across a sloping lawn can sit at 12 centimetres at one end and 40 at the other, which makes the whole structure a planning matter. Measure at the lowest ground point before committing to a height.

What ground conditions and access do to the price

After the sub-frame, the two variables that move a decking quote most are the ones a photograph cannot show.

Ground. Level, free-draining ground takes a straightforward frame on short posts. A slope requires stepped bearers, longer posts and more footings, and every additional 300 millimetres of height adds material and time. Heavy clay, a high water table or made ground means deeper footings, and soft ground can require a concrete pad where slabs would have been used elsewhere.

Access. Timber, aggregate and concrete arrive by the tonne. A side gate wide enough for a barrow is a normal price. Carrying everything through the house, or through a neighbouring property, adds a labour day or more before a single joist is cut — and the same constraint applies in reverse to spoil and old decking going out.

Both belong in the quote conversation before a number is given, because both are the classic source of a mid-job variation. A builder who has walked the access route and dug a trial hole has priced your garden. One who has looked at photographs has priced an average garden, and the difference will be settled later, in their favour. Check the firm is registered with a scheme such as TrustMark at the same time, and the wider sequencing of outdoor trades is set out in the UK outdoor order of trades.

How to read a decking quote before you sign

A decking quote is short, which makes the omissions easy to find once you know what is meant to be there.

1. Board specification and grade. Softwood or composite, capped or uncapped, hollow or solid, with the manufacturer named — because "composite decking" spans a £55 per square metre range on its own.
2. Joist centres and sub-frame timber. Stated in millimetres, with the treatment class, and matched to what the board manufacturer requires rather than to habit.
3. Footing detail. Concrete footings, post anchors or slabs, with depths. This single line separates a deck that lasts from one that moves.
4. Ground preparation. Excavation, weed membrane, aggregate and the ventilated void beneath the boards, each priced rather than assumed.
5. Steps, guarding and edge detail. Priced explicitly, because guarding on a raised deck is a regulatory requirement rather than a styling choice.
6. Disposal and reinstatement. Removing the old structure, taking spoil away, and making good the lawn or paving the works cross.

Then settle the variation rate in writing before work starts, because ground conditions are the honest unknown on this job and a rate agreed under a spade in a trench is never the rate you would have agreed at the kitchen table. Those steps are phases five and six of The 12-Phase System — quote evaluation and contract review — and the pre-start checks that belong alongside them are set out in the UK outdoor project checklist.

If a validated budget is the right first step, use the free Renovation Cost Calculator — a trade-by-trade estimate for your specific project, in under 5 minutes, before anyone has quoted.

Frequently asked questions

How much does decking cost per square metre in the UK in 2026?

Supply only, pressure-treated softwood boards typically run £20 to £45 per square metre and composite boards £37 to £92. Fully installed, including the sub-frame, fixings, ground preparation and labour, timber typically lands at £40 to £108 per square metre and composite at £80 to £200, with mid-range composite most commonly £90 to £135. Raised or difficult sites run £150 to £350.

Is composite decking worth the extra cost?

It depends on how long you intend to own the result. Softwood costs less to buy and carries an annual cleaning and re-treating commitment plus a shorter replacement cycle. Composite costs more to buy and needs washing rather than treating. Under about five years timber usually wins on total spend; beyond ten, composite usually does, and the crossover comes earlier in shaded or wet gardens.

Do I need planning permission for decking in England?

Not where the decking is no more than 30 centimetres above the ground and where the decking and platforms, together with other extensions and outbuildings, cover no more than 50 percent of the garden area. Cross either threshold and an application is required. Listed buildings, conservation areas and Article 4 directions remove those freedoms, and Scotland, Wales and Northern Ireland operate separate systems.

Does a raised deck need a balustrade?

Approved Document K expects pedestrian guarding in dwellings wherever a person could be injured by falling more than 600 millimetres. Its Table 3.1 sets guarding for external balconies and the edges of external floors in single-family dwellings at 1,100 millimetres, against 900 millimetres for internal stairs and landings. Confirm the requirement with building control before building rather than after.

Why is the sub-frame such a large part of the price?

Because a deck is a suspended floor. It takes roughly seven linear metres of joist for every square metre of finished deck, at around £17 per square metre in treated timber before posts, footings, fixings and membrane, and every metre has to be cut, levelled and fixed. That labour is invisible once the boards are down, which is why it is the first thing a cheap quote reduces.

How long does a deck take to build?

A straightforward ground-level deck on level, accessible ground is commonly three to five days for two people. A raised deck with steps and guarding, or a site with restricted access or poor ground, runs to two weeks once footings need to cure before the frame goes on. Ground conditions and access, not the size of the deck, set the duration.