Double-storey extensions in Berkhamsted: design, approvals and build
We design and build double-storey extensions for houses in Berkhamsted, with a written price once the survey and design are done and one point of contact throughout.
- Guide price in BerkhamstedFrom £40,000 inc VAT
- PlanningUsually a householder application
- Build time16–24 weeks on site
- Postcode districtsHP4
What we take care of
- Householder planning application where needed
- Insulation, plastering, electrics and plumbing to finish
- Building regulations drawings and structural design
- Breaking through at both levels, stairs and landing changes where needed
The roof is what makes a two-storey extension look right or wrong. We match the pitch and materials of the main house wherever possible and plan the upstairs layout around the existing landing so the new rooms feel original rather than bolted on.
How much does a double-storey extension cost in Berkhamsted?
These guide figures apply our East of England adjustment (×1.06) to national rates. They include VAT at 20% and cover the build itself; design and council fees are listed separately.
Typical rates in Berkhamsted: £1,640 to £3,180 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| 3 m × 4 m, two floors 24 m² | £40,000 – £48,500 | £45,500 – £60,000 | £58,500 – £76,500 |
| 4 m × 4 m, two floors 32 m² | £52,500 – £63,000 | £61,000 – £80,000 | £78,000 – £102,000 |
| 4 m × 6 m, two floors 48 m² | £78,500 – £94,500 | £91,500 – £120,000 | £117,000 – £153,000 |
Try the guide-price tool to see a range for your own size and finish.
Covering Berkhamsted
Across HP4, we can visit, measure and advise. We also work in nearby Hemel Hempstead (5 miles), Rickmansworth (9 miles), Harpenden (10 miles), St Albans (10 miles).
For homes towards Buckinghamshire, Chesham is around 4 miles away. Across the East of England many houses sit on generous plots, and single-storey and wraparound extensions are a natural fit.
Will the council need to approve it?
In England a two-storey rear extension is permitted development only if it projects no more than 3 m from the original rear wall, sits at least 7 m from the rear boundary, matches the roof pitch and uses obscure, non-opening side windows upstairs. Most two-storey extensions therefore go through a householder planning application, which costs £548 from 1 April 2026 and normally takes about 8 weeks.
Before any drawing is finalised we check whether the house is listed, in a conservation area or subject to an Article 4 direction.
Building over or within 3 m of a public sewer needs the water company's consent, usually through a build-over agreement, before the foundations go in.
If the work involves a shared wall, building on the boundary, or digging foundations within 3 m (sometimes 6 m) of a neighbour's building, the Party Wall etc. Act 1996 applies and notice must be served before work starts: two months for work to a party wall, one month for new walls on the boundary and for excavations.
Applications are decided by the local planning authority (your district, borough or unitary council).
Our process, step by step
Site visits are free and there is no obligation. Where drawings are needed, the design stage is priced in writing before it starts.
Free site visit
A designer visits, takes measurements and photos, and discusses layouts, budget and timing with you.
Design and approvals
We draw the design, agree it with you and handle planning or permitted development checks and building regulations.
Fixed written price
With the design and specification agreed, you get a fixed written price and a start date.
Build and sign-off
Work is carried out to the agreed programme, inspected by building control and signed off at the end.
Common questions in Berkhamsted
Do I need building regulations approval in Berkhamsted?
Yes. Almost every extension needs it, whatever the planning route. We prepare the drawings and book the inspections.
Will my neighbours in Berkhamsted be involved?
If a planning application or prior approval is needed, the council notifies neighbours. If the work is on or near a shared boundary, party wall notices may also be needed.
Do you cover all of Berkhamsted?
Yes. We cover Berkhamsted and the surrounding parts of Hertfordshire. Site visits are free and there is no obligation.
Is a two-storey extension cheaper per square metre?
Usually. Our guide range is about £1,640 to £3,180 per m² of new floor area including VAT, compared with £1,860 to £3,600 per m² for single-storey work, because the foundations and roof are shared across two floors.
Do I need a Party Wall Agreement?
If you are in England or Wales and the work involves a shared wall or digging foundations close to a neighbour, the Party Wall etc. Act 1996 applies and notices must be served before work starts. We tell you which notices are needed.
Book a free site visit in Berkhamsted
We will measure up, check the planning position and give you honest guide figures.
- Free, no-obligation site visit
- Planning route checked before you spend on drawings
- Written price once the design is agreed
- Building control sign-off at the end
Prefer to talk? Call 0800 088 6341 or .
Book a free site visit
Tell us a little about the project and we will arrange a time.