When planning permission is needed
Wandsworth's basement guidance says planning is always needed if:
- the property is a flat
- the building is listed
- you are adding a lightwell
- the work affects front walls, fences or protected trees
Converting an existing cellar, with no change to the outside of the house, may not need planning permission. A lawful development certificate is a good idea in that case, because buyers' solicitors will ask for proof.
Wandsworth's key basement rules
| Rule | What it means for you |
|---|---|
| Single storey only | Wandsworth says multi-level basements are not appropriate in the borough. |
| Keep half the rear garden | Good practice is to keep at least half of the back garden, with at least 1 m of soil above any basement beneath it. |
| Front lightwells | At least 50% of the front garden should remain, with at least 2 m depth, normally required in conservation areas. |
| Construction method statement | Strongly encouraged, and required for listed buildings. It must be independently checked. |
| Flood risk | Many Wandsworth properties are in flood risk areas, so specialist waterproofing design is essential. |
Source: Wandsworth Council basement guidance, checked October 2026.
Other consents you are likely to need
- Building Regulations approval. Always required.
- Party wall agreements with each adjoining neighbour.
- Skip, scaffold or hoarding licences and possibly parking bay suspensions.
- Thames Water approval if you build over or near a public sewer.
- Freeholder consent if the property is leasehold.
How long does it all take?
Allow around 8 weeks for a planning decision once the application is validated, plus time for party wall notices and surveyors. Starting the design early and serving party wall notices in good time keeps the build date on track.
How we help
We have built basements in South West London since 2009. We work with your architect and engineer, prepare the construction method statement, and guide you through party wall and Building Control, so the build starts on a solid footing.
FAQs
Can I build a basement under my garden in Wandsworth?
Possibly, but Wandsworth recommends keeping at least half the rear garden and at least 1 metre of soil above any basement beneath it.
Is a cellar conversion easier than a new basement?
Usually. If you are not changing the outside of the house, you may not need planning permission, and the engineering is simpler.
Does a basement add value?
In much of South West London, extra living space adds value, but it depends on the house and the street. Ask a local estate agent before you commit.