£1,800 to £3,000 per square metre, plus VAT. That's the guide range our extensions in Bristol run at. If you've searched for two storey extension cost and found national averages, this is a Bristol answer instead. A two-storey extension applies that rate to two floors of new space, which is why the totals look big, and why the value per square metre is better than it first appears. Below: two worked examples, why the upstairs costs less, what moves the price, the fees and the time on site.
Two storey extension cost: the short answer and two worked examples
Per square metre means new floor area across both floors. A footprint of 3 m by 5 m gives you 15 m² downstairs and 15 m² upstairs, so 30 m² in all.
| Worked example | Footprint | New floor area | At £1,800/m² | At £3,000/m² |
|---|---|---|---|---|
| Two-storey rear: kitchen-diner below, bedroom above | 3 m × 5 m | 30 m² | £54,000 | £90,000 |
| Two-storey side on a semi: utility and WC below, bedroom and shower room above | 2.5 m × 7 m | 35 m² | £63,000 | £105,000 |
Both are plus VAT at 20%. With VAT, the rear example runs from £64,800 to £108,000, and the side example from £75,600 to £126,000.
These are guide figures, not quotes. Where you land depends on the structure, the glazing, the finish and what's in the scope. Check whether kitchen units, bathroom fittings and flooring are in a builder's price or left to you, because that can move the total a long way. Our quotes are detailed and itemised, and the price only changes if you agree the change first. For a quick feel for your own project, try our cost estimator.
Why the second storey costs less per square metre
Two storeys cost meaningfully less than twice one storey. A lot of an extension's cost sits in things you only pay for once:
- Foundations and groundworks. The footings are sized to carry two floors, but you only dig, pour and connect the drainage once.
- The roof. One roof covers the new space, whether that's one floor or two.
- Scaffold, skips and site set-up. Up once, down once.
- Drawings, calcs, planning and building control. One set of each.
The upper floor adds walls, a floor structure, windows and an opening into the existing first floor. It doesn't add another set of foundations or another roof. Square metre for square metre, the upstairs is the least expensive floor area in the build.
It's often the space that adds the most, too. Nationwide found that a loft conversion or extension adding a double bedroom and bathroom can add as much as 24% to the value of a three-bedroom, one-bathroom house (Nationwide). More detail is on our two-storey extensions page.
What moves the price
- Groundworks. Bristol ground changes from street to street. Clay, tree roots, old drains or a public sewer nearby can all mean deeper or redesigned foundations. If a public sewer runs within three metres of the new walls, Wessex Water's criteria apply (Wessex Water). A drain survey is something you provide. We don't CCTV drains, but we price far more accurately with one.
- Steels. Opening up the back or side of the house on two floors needs beams sized by a structural engineer. Their calculations usually cost £500 to £1,000.
- Kitchens and bathrooms. These are the most fitted-out rooms per square metre. An upstairs bathroom also needs a drainage route down through the new structure.
- Glazing. Wide sliding or bifold doors, big picture windows and rooflights add cost quickly, and every window has to meet the energy rules in the building regulations.
- Roof form. A pitched roof that ties into the main roof, a hipped end, tiles to match an older house.
- Access. No side access means materials and spoil go through the house or over it.
The fees around the build
| Fee | Guide | Notes |
|---|---|---|
| Measured survey and drawings | Set by your architect | Our design and build service works with partner architects |
| Planning application | £548 | Needed for most two-storey schemes |
| Structural engineer's calcs | Usually £500 to £1,000 | Sizes the steels and foundations |
| Building control | Set by your council's charging schedule | You normally apply. We liaise and book inspections, or apply for a small admin fee |
| Party wall surveyors | Depends on the surveyors | Only if a dispute arises. You usually pay both sides' reasonable fees |
| VAT | 20% | Applies to most extension work |
On planning, permitted development covers only a narrow slice of two-storey work. A two-storey rear extension can't go more than 3 m beyond the original rear wall, must be at least 7 m from the boundary opposite, and its roof pitch must match the house as far as practicable (Planning Portal). Side extensions under permitted development are single storey only. So most two-storey schemes need a householder application, which costs £548 and should be decided within 8 weeks of validation (Planning Portal).
If the extension is built up to the boundary or the foundations go near next door's, you'll need party wall notices: one month for a new wall on the boundary or nearby excavation, two months for work to a party wall (GOV.UK). You serve them as the owner. Our party wall page explains what goes in them.
How long it takes on site
Our two-storey extensions typically take 12 to 16 weeks on site. The order: groundworks and drainage, the ground floor, blockwork up to first-floor level, the floor deck, the upper walls, the roof, then windows in so it's weathertight. Only then do we open up into the house, followed by first fix, plastering, second fix, the kitchen and bathroom, and decoration.
You can usually live at home throughout. The disruptive weeks are the two breakthroughs: the wall downstairs and the opening into the upstairs landing or bedroom. On a job like this we leave them as late as the programme allows, sheet off doorways and protect floors. Our site hours are 8am to 5pm, Monday to Friday. There's more on the dust and noise side in our guide to living at home during a build. For the paperwork before all that, see plan in October, build in spring.
Frequently asked questions
How much does a two-storey extension cost in Bristol?
Our guide range is £1,800 to £3,000 per square metre of new floor area, plus VAT. A 3 m by 5 m two-storey rear extension adds 30 m², so about £54,000 to £90,000 plus VAT. Drawings, planning, calcs and building control fees sit on top. You get a detailed, itemised quote after a survey.
Does a two-storey extension cost less per square metre than a single storey?
Usually, yes. The foundations, roof, scaffold and site set-up are paid for once but spread over twice the floor area. The upper floor adds walls, a floor structure and windows, not a second set of foundations or a second roof.
Do I need planning permission for a two-storey extension?
Usually. Permitted development only allows a two-storey rear extension up to 3 m deep, at least 7 m from the rear boundary, with a matching roof pitch. A two-storey side extension always needs permission. A householder application costs £548 and should be decided within 8 weeks of validation.
What fees should I allow on top of the build cost?
Allow for drawings, a £548 planning application, structural calcs at usually £500 to £1,000, building control fees set by your council, and party wall surveyors if a dispute arises with a neighbour. VAT at 20% applies to most extension work.
How long does a two-storey extension take to build?
Typically 12 to 16 weeks on site. Before that, allow for drawings, the 8-week planning decision and any party wall notice periods. You can usually live at home during the build, with the most disruption when we open up into the house.
Free, no-obligation quote. No pressure. Tell us about your extension and we'll come and measure up, then send you a detailed, itemised price.
