2 Storey SIPs Extension
Structural insulated panels are a common way to build a prefab extension over two floors: wall and roof panels made to your plans in a factory, then stood up on site in one short stretch.
£1,300 to £2,400 per m²SIPs extension, finished, national 2026 range including VAT
What a SIPs panel is
A SIP is a sandwich: two sheets of OSB board bonded to a thick core of rigid insulation. The panel carries load, keeps heat in and forms the airtight layer in one piece. Each wall and roof panel is cut to size in the factory, with openings for windows and doors already formed.
For a two storey extension, the ground floor wall panels go up first. The first floor, usually timber joists or a factory-made floor cassette, sits on top of them, then the upper wall panels and the roof. Because nothing is cut or built up course by course on site, the shell is closed against the weather quickly once the panels arrive.
Why SIPs suit two floors
They are light, so the foundations carry less than they would under block walls, and the panels can often be lifted with a small crane or by hand. They are very well insulated for their thickness, which keeps an upstairs bedroom warm and makes the Approved Document L energy targets easier to hit. And because the panels fit together tightly, the finished rooms are less draughty than many older houses.
What a SIPs extension costs
Finished SIPs extensions typically cost £1,300 to £2,400 per m², nationally, including VAT. That covers the whole job, not just the panels. A two storey SIPs extension of 20 m² on each floor would land roughly between £52,000 and £96,000 before any kitchen.
Panel suppliers often quote a price per m² for the shell alone. That is not a finished price. It usually leaves out foundations, the first floor, windows and doors, the outside cladding or brick slips, roofing, wiring, plumbing, plastering and decorating. Ask any supplier to list what is left for your builder.
SIPs against other prefab frames
| Frame | What arrives on site | Suits |
|---|---|---|
| SIPs panels | Insulated wall and roof panels, cut with openings | Rear and side extensions with ordinary spans; tight budgets for heat loss |
| Timber frame panels | Studwork panels, insulated in the factory or on site | Most shapes; builders who know timber frame well |
| Volumetric modules | Finished boxes, one or more per floor | Simple shapes with good crane access and the shortest time on site |
A two storey SIPs extension priced as a finished job, not a panel package.
Get a quoteWhere SIPs need care
Very wide openings, such as a full-width set of sliding doors below a bedroom, need a steel or engineered timber beam above them, designed by the engineer. Heavy wall cupboards and radiators need fixing points planned in. Wiring runs in service voids or chases, so it pays to know where sockets and lights go before the panels are cut.
The OSB faces must stay dry during the build and the finished wall needs a ventilated cladding or render system outside. A builder who has put up SIPs before will know the details; ask how many two storey SIPs jobs they have done.
Planning and building control
A SIPs extension follows exactly the same planning rules as any other two storey extension, and needs building regulations approval. In England, two storeys at the back count as permitted development only up to 3 m out from the original back wall and with 7 m kept clear to the rear boundary; most families apply, for £548. Our planning page covers the detail.
Buying a 2 storey SIPs kit
Some suppliers sell the panels for both floors as a kit, delivered with a fixing schedule, and leave the rest to you or your builder. It can work well if you have a builder who knows SIPs and will take responsibility for the whole job. If you would rather have one firm answer for everything from the foundations to the paint, a full build is simpler.
Sources
- Finished SIPs extension costs: published 2026 UK extension cost guides, national, including VAT.
- Approved Document L, energy efficiency (GOV.UK).
- GOV.UK permitted development technical guidance.
- Planning Portal, planning application fees.
Questions families ask
Are SIPs strong enough for a two storey extension?
Yes. SIPs are load-bearing and are used for whole houses. An engineer designs the panels, the first floor and any beams over wide openings, and building control checks the calculations.
Is a SIPs extension cheaper than brick?
Finished SIPs extensions typically cost £1,300 to £2,400 per m², which can come in below a brick and block build, but the saving depends on the design. The surer gains are a faster weathertight shell and a warm, airtight building.
Can a SIPs extension be clad in brick?
Yes. The outside can be brick, brick slips, render, timber or tiles, so the extension can match the house and meet planning conditions on materials.
Read next
- Foundations and structure
What a panel frame needs from its base.
- Double storey side extensions
Where SIPs and good crane access often go together.
- 2 storey extension cost
Price both floors with the calculator.
Get a quote for your two storey extension
Start with the postcode. Four short questions about the extension follow, then your contact details.
We are an introduction service, free to you, and we do not build. Once we have found a firm near you that puts up two storey extensions, we tell you who it is, and your details stay put until you give the go-ahead.
Got it. Your enquiry has arrived.
- We search for a firm that puts up two storey prefab extensions in your part of the country, then get in touch to tell you who it is.
- Nothing goes to that firm unless you agree.
- The firm visits, looks at the ground and the access for a crane, and prices the job. We never send marketing.