Annexe extensions in Berkhamsted: design, approvals and build
Thinking about an annexe extension for your Berkhamsted home? Start with a free site visit: we measure up, check what the council will allow and give you honest guide figures on the day.
- Guide price in BerkhamstedFrom £58,000 inc VAT
- PlanningUsually a householder application
- Build time16–24 weeks on site
- Postcode districtsHP4
When an annexe extension makes sense
- Relatives who need support close by
- Homes with a large side or rear garden
- Multi-generational families
Accessibility is cheaper to design in than to retrofit. Level access, a 900 mm door width, a level-access shower and space to turn a wheelchair can all be planned into the footprint for little extra cost.
Planning and approvals in Berkhamsted
In England an annexe that stays part of the household and connects to the house is assessed as an extension, but its size usually takes it beyond permitted development, so a householder application describing the ancillary use is the normal route.
Homes in conservation areas, national parks, National Landscapes (formerly AONBs), the Broads and World Heritage Sites have tighter rules, so we always check the property's status and planning history before design starts.
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).
Covering Berkhamsted
We cover Berkhamsted and the postcode districts HP4. The same team covers Hemel Hempstead (5 miles), Rickmansworth (9 miles), Harpenden (10 miles), St Albans (10 miles), all within easy reach.
Just over the Buckinghamshire border, Chesham is about 4 miles away. The East of England mixes market-town terraces, inter-war semis and modern estates. Clay soils are common in parts of the region, which can affect foundation design.
Annexe extension prices 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: £2,120 to £4,030 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| Studio annexe 25 m² | £58,000 – £73,000 | £63,500 – £79,500 | £79,500 – £101,000 |
| One-bedroom annexe 35 m² | £74,000 – £93,000 | £89,000 – £111,500 | £111,000 – £141,000 |
| Larger annexe 45 m² | £95,000 – £119,500 | £114,000 – £143,500 | £143,000 – £181,500 |
Want a range for your exact size? The guide-price tool takes about a minute.
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
Once the layout is agreed, we deal with the council: planning permission or written confirmation that none is needed, plus building control.
Fixed written price
You receive a written, itemised price and programme. Nothing starts until you are happy with it.
Build and sign-off
Work is carried out to the agreed programme, inspected by building control and signed off at the end.
Questions people ask about annexe extensions
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.
Can I see a price before committing to anything?
Yes. The guide prices on this page are adjusted for Berkhamsted, and the guide-price tool gives a range for your own size. After the survey you get a written price before anything is agreed.
Can the annexe have its own front door?
Yes, many do, but it should still connect to the main house to stay clearly part of it.
How much does an annexe extension cost?
Our guide range is about £2,120 to £4,030 per m² including VAT. A one-bedroom annexe of about 35 m² is typically £89,000 to £111,500 at standard spec in Berkhamsted.
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.