Postcode checkerPrime London
Can I build it here?
Enter the postcode and the work. See the council, its rules, the time on site and a value band.
i The checker
Two questions. One answer.
This is a guide, not planning advice. Every site is checked properly before we price it.
Get the full report.
Every rule with its source, the steps in order, and our work nearby. Printable, and yours to keep.
ii The rules everywhere
What applies in every council.
Some rules are national. Each council then adds its own.
- Single storey rear extensions may reach 4 metres detached, 3 metres otherwise. Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1
- Under prior approval, that rises to 8 metres detached or 6 metres otherwise. Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1
- The larger prior approval route does not apply in a conservation area. Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1
- Roof additions are capped at 40 cubic metres on a terrace, 50 otherwise. Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1
- Roof permitted development does not apply in a conservation area. Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1
- Flats and maisonettes have no householder permitted development rights. General Permitted Development Order 2015, Article 2
- Listed building consent is needed for any works affecting a listed building’s character. Planning (Listed Buildings and Conservation Areas) Act 1990, section 7
- Painting unpainted surfaces of a listed building is likely to need consent. Historic England, Listed Building Consent Advice Note 16
- Party structure notices go out at least two months before the work. Party Wall etc. Act 1996, section 3
- Excavating within 3 or 6 metres of a neighbour needs one month’s notice. GOV.UK, The Party Wall etc. Act 1996: explanatory booklet
- Electrical work in a home must meet Building Regulations Part P. GOV.UK, Electrical safety: Approved Document P
Checked 25 October 2026. Each line links to its source.
iii The steps
From an idea to a start on site.
- Check the council and the rulesFind which council covers the house. Read its rules for the work you want.
- Book a free visitNick visits the house. He tells you plainly what looks possible.
- Get a budget estimateOur quantity surveyor prices the brief. It typically follows within seven days.
- Design and applyOur architectural team draws the scheme. We apply for planning, or confirm it is not needed.
- Serve party wall noticesNotices go to the neighbours, one or two months ahead of the work.
- Agree the price and the programmeA cost plan is built line by line from the drawings. The programme is fixed with it.
- Start on siteConditions are discharged, the construction plan is agreed, and the build begins.
iv Questions
What people ask us.
Do I need planning permission for a basement in Kensington?
Yes. Kensington and Chelsea treats a new basement as development needing permission.
Policy CD11 allows one storey, under no more than half of each garden.
A Construction Traffic Management Plan goes in with the application.
Source: Kensington and Chelsea Local Plan 2024, Kensington and Chelsea Basements SPD, April 2016
Can I build a basement in Chelsea under a listed house?
No. The borough allows no excavation under a listed building.
That includes its vaults. A garden basement may still be possible.
We check the listing and the garden before anything is drawn.
How big can a basement be in Westminster?
Policy 50 allows one storey below the lowest original floor.
It may run under no more than half the garden.
A citywide Article 4 direction removes basement permitted development.
Source: Westminster City Plan 2019 to 2040, January 2026 edition, Westminster City Council, Article 4 Directions in Westminster
Can I dig a basement in Fulham?
Often, with planning permission. Policy DC11 allows one storey.
It may reach half the house’s depth and half the garden’s.
An Article 4 direction has covered basements since April 2018.
Source: Hammersmith and Fulham Local Plan 2018, Hammersmith and Fulham basement Article 4 Direction, confirmation notice
Is a rear extension permitted development in London?
Sometimes. A single storey may reach 3 metres, or 4 metres if detached.
Prior approval can take that to 6 or 8 metres.
That larger route does not apply in a conservation area. Flats have no such rights.
Source: Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1, General Permitted Development Order 2015, Article 2
Do I need planning permission for a loft in a conservation area?
Usually, yes. Roof permitted development does not apply in a conservation area.
Most of Kensington, Chelsea and Westminster is conservation area.
A mansard is drawn and applied for with the council.
Source: Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1, Royal Borough of Kensington and Chelsea, Conservation areas, Westminster City Council, Conservation areas
Do I need a party wall agreement for a basement?
Almost always. Digging near a neighbour needs notice under the Party Wall etc. Act 1996.
Excavating within 3 or 6 metres needs one month’s notice.
Work to the party wall itself needs two months.
Source: GOV.UK, The Party Wall etc. Act 1996: explanatory booklet, Party Wall etc. Act 1996, section 3
What is an Article 4 direction?
It is a council order that removes some permitted development rights.
Work it covers then needs a planning application.
Westminster, Hammersmith and Fulham and Camden each have one for basements.
Source: Westminster City Council, Article 4 Directions in Westminster, Hammersmith and Fulham basement Article 4 Direction, confirmation notice, Camden Planning Guidance: Basements, January 2021
Can I build a basement in Hampstead?
Camden’s Policy A5 allows one storey, never under an existing basement.
It must not exceed half of each garden.
A Basement Impact Assessment is audited independently, at the applicant’s cost.
Source: Camden Local Plan 2017, Camden Planning Guidance: Basements, January 2021
How long does a London basement take to build?
Typically 12 to 16 months on site, by our own programme model.
Design, planning and party wall notices come before that.
We set out your programme after a free visit.
Every site is different. We check yours.
Nick visits, and tells you plainly what looks possible. The visit is free.
Send us a messageCall 020 7731 6841
This is a guide, not planning advice. Every site is checked properly before we price it.
