Timber frame extension cost
A timber frame extension typically costs £1,400 to £2,400 per m² including VAT, built and finished. That puts a 20 m² room at £28,000 to £48,000 and a 30 m² room at £42,000 to £72,000. Set your own size below.
25 m² single storey, mid finish
£45,000 to £52,500
including VAT. A guide, not a quote.
- Before VAT at 20%
- Rate used
- Same size in brick and block
- Piles
Your size and type go into the form with you.
Prices by size and finish
Single storey, including VAT, on firm ground. The plain column assumes render or brick slips and uPVC windows; the high column assumes wide aluminium glazing, a vaulted or lantern roof and hardwood cladding.
| Floor area | Plain finish | Mid finish | High finish |
|---|---|---|---|
| 12 m² | £17,000 to £21,500 | £21,500 to £25,000 | £25,000 to £29,000 |
| 16 m² | £22,500 to £29,000 | £29,000 to £33,500 | £33,500 to £38,500 |
| 20 m² | £28,000 to £36,000 | £36,000 to £42,000 | £42,000 to £48,000 |
| 25 m² | £35,000 to £45,000 | £45,000 to £52,500 | £52,500 to £60,000 |
| 30 m² | £42,000 to £54,000 | £54,000 to £63,000 | £63,000 to £72,000 |
| 40 m² | £56,000 to £72,000 | £72,000 to £84,000 | £84,000 to £96,000 |
| Rate per m² | £1,400 to £1,800 | £1,800 to £2,100 | £2,100 to £2,400 |
Two storeys, and kits
Two-storey rates are per m² of both floors added together. Frame kits are priced per project by each supplier, and what they include varies, so we give no national kit figure; foundations, cladding, roofing and all inside work are still to pay for.
| What | Before VAT | With VAT |
|---|---|---|
| 30 m² over two storeysA 15 m² footprint | £35,000 to £60,000 | £42,000 to £72,000 |
| 40 m² over two storeysA 20 m² footprint | £46,500 to £80,000 | £56,000 to £96,000 |
| 60 m² over two storeysA 30 m² footprint | £70,000 to £120,000 | £84,000 to £144,000 |
What sits on top of the build price
None of these is in the per m² rate. Professional fees together usually come to 10% to 15% of the build cost, so £6,000 to £9,000 on a £60,000 extension; keep a further 10% to 15% as contingency.
| Item | Typical cost including VAT |
|---|---|
| Raft foundation in place of trench footingsSoft or filled ground | add £2,000 to £3,000 |
| Piled foundationShrinkable clay close to trees, or deep made ground | Priced by your engineer after a ground investigation; can add several thousand pounds |
| Architect or architectural designer, planning drawingsSurvey and planning drawings; a full service is usually 3% to 15% of the build cost | £1,000 to £2,500 |
| Structural engineer, single storeyBeams, foundations and the opening into the house | £600 to £1,200 |
| Structural engineer, two storeysMore openings and a floor to carry | £800 to £1,800 |
| Building control, single storey of 10 to 40 m²Plan approval and inspections; each council sets its own fees | £700 to £1,100 |
| Building control, two storeysUp to about 40 m² | £900 to £1,300 |
| Party wall surveyor, per neighbour, one agreed surveyorOnly if a neighbour dissents to your notice; more if each side appoints its own surveyor, and you pay for both | £700 to £1,500 |
| Planning fee for a householder applicationEngland, where permitted development does not cover the design | £548 |
| Lawful development certificateEngland, optional written proof that no application is needed | £274 |
Where these prices come from
Build rates, foundation allowances and professional fees are typical national ranges for 2026, including VAT. They are not offers from any firm. London and the South East usually cost 20 to 40% more. Planning fees are set by MHCLG from 1 April 2026; building control charges are set by each council or approver.
Where the money goes
The frame is a smaller share than people expect. Even bought as a complete kit, the timber structure comes to well under half of a finished single-storey room. Groundworks, windows and doors, the roof covering and cladding, then electrics, heating, plastering, flooring and decoration make up the rest.
That is why choosing timber frame over blockwork does not transform the price. It changes one layer of the wall. The slab, the roof finish, the glazing and every trade that works inside are identical however the walls go up.
Six things that shift the price
Size, but not in a straight line. Small extensions cost more per m² because the fixed items (design, building control, setting up site, one steel beam, one set of doors) are spread over less floor. Below about 15 m², expect to be near the top of each range.
Glazing. Glass costs several times what an insulated wall does. Each extra metre of sliding door also means a longer beam above it.
Cladding. Render on a carrier board is cheapest. A brick skin adds a bricklayer, wider foundations and wall ties. Larch and cedar boards sit in between; charred or thermally modified timber is at the top.
The roof. A flat warm roof with a membrane is the economical choice. Pitched and tiled costs more in structure and covering, and a vaulted ceiling with exposed rafters more again.
Ground and drains. Clay soil near mature trees can push footings from 1 m deep to 2 m or onto piles. A shared sewer under the footprint brings a build-over agreement and often a diverted run.
The old house. Removing a load-bearing back wall, moving a boiler, rewiring a consumer unit that cannot take a new circuit: alterations to the existing building are priced by the day and are the commonest cause of extras.
Against brick and block
A single-storey masonry extension typically costs £1,800 to £3,000 per m² and a timber frame one £1,400 to £2,400 per m², both including VAT. Once finishes are matched the gap on 25 m² is usually a few thousand pounds at most, and speed can add to timber frame's advantage.
Speed is worth money in three places. Scaffolding and site welfare are hired by the week. A builder who can finish in ten weeks instead of fourteen can price less overhead. And if you are renting elsewhere or paying two mortgages while work is done, each week saved is a week's rent.
The exception is a very small, simple extension built by a local bricklayer with no main contractor. A workshop will rarely beat that on price.
Keeping the cost down
Keep the plan a rectangle and the roof one plane. Corners, steps and valleys each add panels, flashings and labour.
Size the doors to a standard product. A 3 m or 4 m slider off the shelf costs far less than a made-to-measure 4.6 m one, and needs a lighter beam.
Fix the design before the frame is ordered. Workshop panels are cheap to change on a drawing and expensive to change in timber.
Consider buying a frame kit and employing a builder for the rest if you have time to manage it. And ask each firm what its price leaves out. The cheapest quote is often the one with the longest list of exclusions.
Questions about timber frame costs
How much does a timber frame extension cost per m²?
£1,400 to £2,400 per m² including VAT for a finished single-storey room, depending on glazing and cladding; bespoke work can cost more. Two-storey work sits in the same range per m² of total floor. London and the South East usually cost 20 to 40% more.
Is timber frame cheaper than brick and block?
Often a little, on paper. A single-storey masonry extension typically costs £1,800 to £3,000 per m² and a timber frame one £1,400 to £2,400 per m², both including VAT. Once finishes are matched the gap narrows, and timber frame adds a shorter programme: less scaffold hire, fewer weeks of site costs and an earlier move-in.
What does the price include?
Standard foundations and slab, the frame, roof, cladding, windows and doors, insulation, electrics, heating, plastering, flooring and decoration. It leaves out kitchen units and appliances, bathroom fittings, professional fees and planning fees. VAT is included.
Why is there such a wide range?
Glazing is the biggest swing: a 5 m run of aluminium sliding doors with rooflights above costs many times what French doors and a window do. Cladding, roof shape and how much of the old house is altered account for most of the rest.
Do I pay VAT on a timber frame extension?
Yes, at 20% on labour and materials. Extensions to existing homes are standard-rated, and the refund scheme for DIY housebuilders does not cover them. HMRC's Notice 708 lists the narrow exceptions.
How close is the calculator to a real quote?
Treat it as a budget tool. It multiplies your floor area by national rates and adds an allowance for difficult ground. A firm quoting from drawings will be more precise, and may land outside the range if the site is awkward or the design unusual.
Are prices different in Scotland?
Building rates match those elsewhere in the UK outside London. The fees differ: a building warrant replaces the building regulations application and its fee is set on a sliding scale by the value of the work.
More to read
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