A double-storey extension adds two floors of new space to your house in one build, typically a larger kitchen or living room downstairs with an extra bedroom, bathroom or en-suite above, sharing one set of foundations and one roof.
Anyone planning a double-storey extension in St Helens wants three things: a clear price, a realistic timetable and a tidy job. We publish a guide of £57,000–£114,000 including VAT for the North West up front, explain that work normally takes 14–22 weeks on site, and confirm both in writing after a free survey of your property.
- Guide price
- £57,000–£114,000 inc VAT
- Time on site
- 14–22 weeks on site
- Postcodes
- WA9, WA10 and WA11
- Planning rules
- England
- Local area
- Merseyside
- Survey
- Free, with a written quote
Double-storey extensions prices in St Helens
Here is how the guide price for a double-storey extension breaks down in St Helens. We start from national figures and adjust for the North West, which comes out about 5% below the national guide. The resulting range, VAT included, is £57,000–£114,000, and a survey, at no cost to you, firms it up.
| Type of job | What it usually involves | Guide in St Helens |
|---|---|---|
| Small (15–20m² total) | A compact rear or side extension adding a small room on each floor. | £38,000–£62,000 |
| Typical (30–40m² total) | A larger kitchen or living room below with a double bedroom or en-suite above. | £57,000–£114,000 |
| Large (50m² plus total) | Wide or deep extensions, often with a new bathroom, steelwork and high-spec glazing. | £95,000–£171,000 |
What moves the price up or down:
- Combined floor area across both storeys
- How the new roof joins the existing roof
- Bathrooms, en-suites and plumbing on the upper floor
- Scaffolding duration, access and the level of finishes
What’s included?
- Groundworks, foundations and below-ground drainage
- First-floor joists, stud walls and new openings upstairs
- Roof structure tied into the existing roof, tiled to match
- Electrics, plumbing and heating by qualified trades, with certificates
- Windows, external doors, plastering and internal doors
- Building control inspections and completion certificate
Local housing and a double-storey extension
Liverpool's housing includes Georgian terraces near the centre, large areas of Victorian red-brick terraces, Edwardian semis in the suburbs and big interwar council estates. The Wirral has Victorian villas and interwar semis, Southport has Victorian villas and bungalows, and St Helens and Knowsley have post-war estates and newer housing.
Terraces suit loft rooms, kitchen extensions and repointing, and many need their roofs and windows renewed. Suburban semis commonly take side extensions, driveways and porches.
That variety is why a guide price for a double-storey extension in St Helens is only a starting point; the survey shows what your particular property needs.
Permissions for a double-storey extension in St Helens
For anyone in St Helens, the relevant framework is England's. The summary below is general, so we always contact the council about your address before putting a price in writing.
In England, a two-storey rear extension can only be permitted development if it is no more than 3 m deep, at least 7 m from the rear boundary and finished to match the house. Most double-storey and all two-storey side extensions need full planning permission.
Building Regulations approval is needed, with structural calculations for beams, foundations and the roof. The Party Wall etc. Act 1996 often applies on semi-detached and terraced houses.
Rules change and every property is different, so we check the planning history and constraints for your address before we quote.
The four stages
Free site survey
We arrange a free site survey on a date convenient to you. We measure up, look at the existing structure and access, and discuss your plans for a double-storey extension so the price reflects your home.
Price and scope agreed
We put everything into a written, fixed-price quote: the specification, what's excluded, staged payments and the expected time on site. Take whatever time you need to decide; there's no pressure to commit.
Getting ready
Before anyone starts, we confirm the programme in writing, check whether consents are required and arrange deliveries. If a skip or scaffolding on the road needs a permit, we apply for it.
Finish and handover
Our trades complete a double-storey extension while your point of contact keeps you updated. When everything is finished, we clear the site, take away waste and go through the result with you before handover.
Working with SK Home Improvements
Common questions
Do I need planning permission for a two-storey extension?
Most two-storey extensions need planning permission, but it depends on the size, height and position, your home's location, whether it is listed or in a conservation area, and which UK nation you are in. In England, a two-storey rear extension can sometimes be built under permitted development if it is no deeper than 3m and at least 7m from the rear boundary. We check what applies before quoting.
Do you cover Prescot, Ashton in Makerfield and Huyton?
Yes. As well as St Helens, we cover Prescot, Ashton in Makerfield and Huyton and the rest of Merseyside. Our coverage is UK-wide, so the process is the same wherever you are: a free site survey, a quote in writing that fixes the price for the agreed scope, and one point of contact while the work is planned and carried out.
Can we live at home while it is built?
Most families stay at home during a double-storey extension. The new structure is built outside first, and we only break through into the existing rooms near the end, usually one floor at a time. Upstairs, this may mean a bedroom is out of use for a week or two. We fit dust screens, protect floors and stairs, and plan any time without water or power in advance.
How long will a double-storey extension take?
On a typical home, allow 14–22 weeks on site. Larger projects, older buildings and extra work found once things are opened up can extend that, while simpler jobs may be shorter. Your quote includes an estimate of time on site, and your point of contact keeps you updated on the programme as the work progresses.
Can the new upstairs room have its own bathroom?
A new upstairs room can usually have an en-suite, provided waste pipes can reach the soil stack or a new one can be installed. Running the waste pipe to the right falls is the main design question, and a pumped system is an option where gravity will not work. We plan bathroom positions at the design stage so pipes, ventilation and insulation are built in rather than added later.
Also covering areas around St Helens
Whether you're in the centre of St Helens or on its outskirts, WA9, WA10 and WA11 addresses are covered. We extend the same service, and the same fixed-price approach, to Prescot, Ashton in Makerfield and Huyton.