Basement conversion planning permission in London
Digging out new basement space under a London home often needs planning permission, and a party wall notice near a neighbour, while fitting out an existing cellar can need less. A householder application costs £548 and the council has 8 weeks to decide it. Our drawings for an existing cellar start at £1,995.
Prefer to talk it through?
Excavating new space and fitting out a cellar are different jobs
Two different projects share the name. A new basement means excavation, underpinning and often a lightwell. An existing cellar already has walls and a floor, and the work is lining, tanking and finishing it.
Decide which of the two you are doing before you ask the council anything. The answer changes the drawings, the structural design and the application. Our basement conversion drawings page shows how we scope each type.
What the council charges and how long it has
From 1 April 2026 the statutory fee for a householder application for alterations or extensions to a single dwellinghouse is £548, as set out in the government's annual planning fee indexation notice. The council has 8 weeks, beginning the day after it receives the application, to decide an application that is not major development (DMPO 2015, article 34(2)(b)).
You and the council can agree in writing to extend that period.
Our analysis of MHCLG planning application statistics, table PS2 (released 24 Sep 2026), counts 145,609 householder decisions across England in the four quarters from 2025 Q3 to 2026 Q2.
Party wall rules apply to a basement even where planning does not
Under section 6 of the Party Wall etc. Act 1996 you must notify an adjoining owner if you excavate within three metres of their building, below the level of its foundations. The distance rises to six metres where your excavation meets a 45-degree line drawn down from their foundations (Party Wall etc. Act 1996, section 6).
The notice must be served at least one month before you begin to excavate, so build that month into your programme. Our guide to the party wall agreement explains the steps.
How busy is the householder route?
Our analysis of MHCLG planning application statistics, table PS2 (released 24 Sep 2026), counts 145,609 householder decisions across England in the four quarters from 2025 Q3 to 2026 Q2. Householder applications are the standard route for work to a single home, and a basement scheme in that category joins a large, well-practised queue.
Boroughs differ in how they treat basements, and some publish their own guidance. Read your borough's before design starts.
Our fee and the next step
Our fixed fee for basement conversion drawings of an existing cellar starts at £1,995. A new excavation is priced after we see the site. For the whole budget, see our basement conversion cost guide.
Building Regulations are a separate approval. Our Building Regulations drawings cover the structure, waterproofing, ventilation and escape.
Sources
Every figure on this page, where it comes from and a link to the original.
| Figure | Source | Link |
|---|---|---|
| 145,609 | Our analysis of MHCLG planning application statistics, table PS2 (district open data table) (released 24 Sep 2026, quarters to 2026 Q2) | www.gov.uk |
| three metres | Party Wall etc. Act 1996 s6(1): excavating within three metres measured horizontally of an adjoining owner's building or structure below its foundations (source wording: three metres) | www.legislation.gov.uk |
| six metres | Party Wall etc. Act 1996 s6(2): excavating within six metres measured horizontally of an adjoining owner's building where it meets a 45-degree plane drawn down from its foundations (source wording: six metres) | www.legislation.gov.uk |
| one month | Party Wall etc. Act 1996 s6(5): notice of the proposed excavation served at least one month before beginning to excavate (source wording: one month) | www.legislation.gov.uk |
| 8 weeks | DMPO 2015 art 34(2)(b): decision period for an application that is not major development (source wording: 8 weeks beginning with the day immediately following receipt) | www.legislation.gov.uk |
| £548 | Statutory fee from 1 April 2026, SI 2012/2920 Sch 1 Pt 2 category 6(1): householder application for alterations or extensions to a single dwellinghouse | assets.publishing.service.gov.uk |
| £1,995 | DrawingsDirect starting fixed fee for basement conversion drawings (existing cellar), from the published price list | drawingsdirect.co.uk |
Questions people ask
Do I need planning permission to convert an existing cellar?
When must I serve a party wall notice for a basement?
Does a basement conversion also need Building Regulations approval?
Photographs: David Hawgood (CC BY-SA 2.0); Peikko (Public Domain).
