Basement and cellar conversions in Finchley

Covering Finchley

Our coverage around Finchley (N3) also includes Muswell Hill (2 miles to the east) and Cricklewood.

Homes in London

Much of London’s housing is Victorian and Edwardian terraces, which is why side return extensions, rear dormers and mansards are so common. Many streets are in conservation areas, and several boroughs use Article 4 directions that remove some permitted development rights.

What is included in a basement conversion in Finchley?

Everything below ground depends on keeping water out. We design the waterproofing system (usually a cavity drain membrane with a pump, or tanking) to the relevant British Standard guidance, then add insulation, ventilation, light and an escape route. New basements involve underpinning and a party wall process and are designed with a structural engineer.

Damp and structural survey
Underpinning or lowering the floor where needed
Lightwells and windows for daylight and escape

How much should I budget for a basement conversion?

Guide prices for basement and cellar conversions, including VAT where it applies. Your fixed price is confirmed in writing after the survey.

Basement and cellar conversions	Guide price incl. VAT
Existing cellar conversion	£1,900 to £3,000 per m²
New basement excavation	£4,200 to £6,600 per m²

What approvals does a basement conversion need in England?

In England we deal with the council’s planning team for permission or a lawful development certificate, with building control (the council or a registered building control approver) for inspections, and with neighbours under the Party Wall etc. Act 1996 where it applies.

Converting an existing cellar with no external changes usually does not need planning permission in England.

What should Finchley homeowners check first?

New basements nearly always involve the Party Wall Act in England and Wales.
Headroom of about 2.1 m or more is needed, which may mean lowering the floor.

What are the steps?

Start with a conversation. A short call or the online form is enough for us to understand what you want to build.
Free site visit. We measure up, look at access, drains and the structure, and talk through options and budget.
Design and fixed price. You get drawings and a written price for the agreed specification before anything is ordered.
We build it. Work follows an agreed programme, with inspections at each stage and a final sign-off.

Questions about a basement conversion in Finchley

Does a cellar conversion need planning permission?

Usually not if nothing changes outside. New basements and lightwells often do.

How long does it take?

About 6 to 12 weeks for a cellar conversion and 16 to 30 weeks for a new basement.

How do I get a price for basement and cellar conversions in Finchley?

Use the guide price tool for a ballpark figure, then book a visit for a fixed written price for the agreed specification.

Other towns nearby

Learn more about basement and cellar conversions, or see every project we cover in Finchley.