SIPs Extension Cost Calculator
A SIPs extension costs £1,300 to £2,400 per m² of floor in the UK, built and finished, including VAT. Set the type, the floor area and the finish below to turn that into a budget for your house.
SIPs extension prices by size
Single storey, built and finished, including VAT. The last column is the SIPs shell alone, which is not a finished price.
| Floor area | Standard | Mid | High spec | Shell only, not finished |
|---|---|---|---|---|
| 12 m² | £15,500 to £20,500 | £20,500 to £25,000 | £25,000 to £29,000 | £14,500 to £21,500 |
| 16 m² | £21,000 to £27,000 | £27,000 to £33,500 | £33,500 to £38,500 | £19,000 to £29,000 |
| 20 m² | £26,000 to £34,000 | £34,000 to £42,000 | £42,000 to £48,000 | £24,000 to £36,000 |
| 25 m² | £32,500 to £42,500 | £42,500 to £52,500 | £52,500 to £60,000 | £30,000 to £45,000 |
| 30 m² | £39,000 to £51,000 | £51,000 to £63,000 | £63,000 to £72,000 | £36,000 to £54,000 |
| 40 m² | £52,000 to £68,000 | £68,000 to £84,000 | £84,000 to £96,000 | £48,000 to £72,000 |
| 50 m² | £65,000 to £85,000 | £85,000 to £105,000 | £105,000 to £120,000 | £60,000 to £90,000 |
Typical national ranges for 2026, including VAT, rounded to the nearest £500. London and the South East usually cost 20 to 40% more. A guide, not a quote.
What sits on top of the build figure
The calculator covers the extension itself on ordinary strip foundations. These are the costs it leaves out.
| Item | Typical price, including VAT |
|---|---|
| Architect or architectural designer, planning drawingsPlanning drawings; a full service is usually 3% to 15% of the build cost | £1,000 to £2,500 |
| Structural engineer, single storeyOften included by the panel supplier for the shell | £600 to £1,200 |
| Structural engineer, two storeysPanels, the new floor and beams | £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 |
| Party wall surveyor, per neighbour, one agreed surveyorOnly where the Party Wall Act applies; more if each side appoints its own surveyor, and you pay for both | £700 to £1,500 |
| Planning applicationHouseholder fee in England, if permitted development does not cover you | £548 |
| Lawful development certificateOptional proof that no application was needed | £274 |
| Reinforced raft, in place of stripSoft or variable ground | £3,000 to £6,000 |
| Piles or screw piles with a ring beamTrees close by, poor ground or no digger access | Priced by your engineer after a ground investigation; can add several thousand pounds |
SIPs against other ways to build
Typical national ranges, per m² of finished floor.
| Method | Per m², including VAT |
|---|---|
| Brick and blockSlowest on site; thickest walls | £1,800 to £3,000 per m² |
| Factory timber frameOpen or closed panels, insulated between studs | £1,400 to £2,400 per m² |
| SIPsStructure and insulation in one panel | £1,300 to £2,400 per m² |
Where these figures come from
Typical national ranges for 2026, including VAT; London and the South East usually cost 20 to 40% more. The £1,300 to £2,400 per m² band is for a finished SIPs extension; dividing it into Standard, Mid and High spec steps is our own working, so that the calculator can respond to finish. The shell figure of £1,200 to £1,800 per m² is for the panels alone and is not a finished price. Planning fees are set by MHCLG from 1 April 2026.
What moves the price
Glass. Nothing shifts a quote faster. A three-metre set of aluminium sliding doors costs several times what the same area of panel does, needs a beam over it, and brings the roof lights with it for balance. If the budget is tight, shorten the glazing before you shrink the room.
Roof shape. A flat or single-pitch roof is the cheapest to panel. A vaulted roof needs a ridge beam and longer panels; see SIPs roof panels.
Small footprints. A 12 m² extension still needs a delivery, a lifting machine, an engineer and a building control fee. Those fixed costs push small rooms towards the top of the range per m² and let large ones drift down.
The ground. The calculator assumes plain strip foundations. Clay with trees, made ground or a sewer under the footprint can add several thousand pounds, and piles are priced by your engineer after a ground investigation; our foundations page sets out the options.
Access. Panels arrive on a rigid or articulated lorry and the roof panels are lifted by machine. A terraced house with no rear access is still buildable, since wall panels can be carried through, but expect a crane over the roof and a road permit.
The three finish levels
Standard, £1,300 to £1,700 per m². uPVC or entry aluminium doors, one roof light, laminate or vinyl floor, painted plaster. A sound, plain room.
Mid, £1,700 to £2,100 per m². Aluminium sliding or bifold doors, two roof lights, engineered timber floor, underfloor heating. This is where most kitchen extensions land.
High spec, £2,100 to £2,400 per m². Wide-span glazing, triple glazing, vaulted roof, bespoke cladding and joinery. Projects with structural glass or a great deal of bespoke joinery can go beyond the typical band altogether.
Where you live
These are national figures. Labour is the part that varies: London and the South East usually cost 20 to 40% more than the national range, and parts of the North, Wales and Scotland a little below it. Panel prices themselves barely change with postcode, though a long delivery run adds haulage.
Kit or finished build
A SIPs extension kit buys the structural shell, typically £1,200 to £1,800 per m² including VAT. That is a shell price, not a finished one. The finished figure buys a room. The difference pays for foundations, the crew who stand the panels, cladding, roofing, glazing, electrics, heating and plaster. Running those trades yourself can save money, but only if your time is free and nothing has to be done twice.
A calculator gives you a range. A firm that has seen your drawings gives you a number.
Get a quoteSIPs extension cost questions
What is the cost of a SIPs extension per m²?
Typically £1,300 to £2,400 per m² of floor, built and finished, including VAT. We split that band into three steps by finish. The SIPs shell on its own, which is not a finished price, is about £1,200 to £1,800 per m².
What does a 20 m² SIPs extension cost?
Between £26,000 and £48,000 including VAT depending on finish, so £21,500 to £40,000 before VAT. Design fees and building control are extra.
Is the calculator accurate?
It is as good as the ranges behind it, which are typical national figures. It cannot see your ground, your access or how much glass you want. Treat the result as a budget to test against real quotes.
Is SIPs dearer per m² than brick?
Not usually. A finished SIPs extension typically costs £1,300 to £2,400 per m² and a single-storey brick and block one £1,800 to £3,000 per m², both including VAT, and the ranges overlap. The panels are a manufactured product with the design work done up front; what you gain most clearly is a shorter build, a thinner wall for the same insulation and very low air leakage.
Is VAT charged on a SIPs extension?
Yes, at 20%, on both kits and building work. The zero rate applies to new homes, not to extending an existing one. See VAT Notice 708.
Does the figure include the kitchen?
No. These figures stop at a finished, decorated room with heating, lighting and sockets. Kitchen units, worktops and appliances are budgeted separately; a kitchen fit-out typically adds £15,000 to £35,000.
Read next
- SIPs extension kits
What the supply-only price includes.
- Two-storey SIPs extensions
Budgets across both floors.
- Foundations
Strip, raft and pile costs.
- What are SIPs?
What you are paying for.
Get a quote for your SIPs extension
Postcode, four quick questions about the build, then how to reach you. It takes about a minute and costs nothing.
We match homeowners with panel firms, free of charge, and do not build extensions ourselves. We look for a company that designs and erects SIPs extensions near your postcode and tell you its name. Your details go no further until you say yes.
Thank you. That is all we need for now.
- We look for a firm that builds SIPs extensions around your postcode, then ring or email you with its name, normally within a working day.
- If you are happy with that firm, say so and we pass your enquiry to them. If not, it ends there.
- They ask for your drawings or come and measure, then price the job. We never send marketing.