Two Storey Prefab Extension
A bedroom upstairs, more room downstairs, and a frame built in a factory so the work at your house is over sooner.
Get a quoteTwo floors, built off site
A two storey prefab extension is made as panels or finished boxes in a factory, then lifted onto new foundations at the back or side of your house. The ground floor usually becomes a kitchen and family room; the floor above takes a bedroom, often with a shower room.
Timber frame, SIPs and steel-framed modules all count. Each gets the same planning rules and building control checks as a brick extension. The difference is that the shell goes up quickly once the base is ready.
What two floors cost
- Two storeys, both floors counted, complete and ready to use
- £1,700 to £2,900 per m²
- Factory-built modular or prefab extension, finished and fitted
- £2,100 to £3,300 per m²
- Householder planning application in England, from 1 April 2026
- £548
- Building control for a two storey extension, set by each council
- £900 to £1,300
National 2026 figures, VAT included. Jobs in London and the South East usually run 20 to 40% above them. A guide, not a quote. Prefab does not cost much less; it saves time on site. Work out your own figure with the calculator.
Where these figures come from
- Build costs per m²: national ranges from published 2026 UK extension cost guides, including VAT.
- Planning fee: Planning Portal, planning application fees (MHCLG fee table, 1 April 2026).
- Building control: council charge schedules for 2026/27. Each council sets its own fees.
The order of work
Drawings and permission
Plans for both floors, then a householder application. Most two storey schemes need one, and councils aim to decide them in eight weeks.
Engineer and ground
A structural engineer sizes the foundations for two floors and the steel where the back wall opens up. Trial holes show what the ground will take.
Factory build
Wall, floor and roof panels, or whole boxes, are made to the drawings while the foundations go in. Weather does not stop this part.
Lift day and fit-out
A crane sets the ground floor, then the upper floor and roof. Windows, wiring, plastering and the bathroom follow from inside.
Questions families ask
Is a two storey prefab extension cheaper than building in brick and block?
Not by much, if at all. Finished prefab and factory-built extensions land somewhere in £2,100 to £3,300 per m², which overlaps a traditional two storey build at £1,700 to £2,900 per m². What you save is time on site: fewer weeks of scaffolding, mess and a house open to the weather.
Can I buy a 2 storey prefab extension kit in the UK?
Yes. Some suppliers sell the frame for both floors as a panel package, from timber frame to SIPs. A kit price covers the frame only. You still pay for foundations, the engineer, building control, windows, roofing, wiring and plumbing, so ask any supplier what is left for your builder before you compare figures.
Will a two storey extension need planning permission?
Usually. In England, permitted development only covers a two storey extension that sticks out no more than 3 m beyond the original back wall and keeps 7 m clear of the rear boundary, with a matching roof pitch and obscure, fixed side windows upstairs. Most families need a householder application, which costs £548. Our planning page goes through it.
Will my existing foundations take a second storey?
The new part gets its own foundations, sized by an engineer for two floors and a roof. The house wall it joins usually carries a steel beam where you open up the ground floor. Clay near trees can mean deeper foundations or piles.
How do the panels or modules get to the back of the house?
By crane, in most cases over the house or along a side drive. Budget about £1,400 for a day's contract lift: a 25 t crane and the crew who plan and sling each load. Tight access is the usual reason a lift runs into a second day, so tell the firms about it up front.
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.