Basement conversions in Fulham
Cellar conversions and full basement digs with underpinning and tanking.
Converting an existing Fulham cellar costs £2,500–£4,000 per square metre; digging a new basement under the house is £4,500–£7,000 per square metre once underpinning and structural work are included. Hammersmith and Fulham restricts basement development, so the planning position matters more here than the build cost.
Consider this if
- There is an existing cellar that is damp and unused
- You have run out of ways to extend up or out
- You want a media room, gym or guest suite
- The house is in a conservation area where extending is restricted
- You need a utility and plant room to free up space above
- The garden is too small to lose to a rear extension
What's included
- Honest feasibility on planning and ground conditions before design
- Structural engineer and underpinning design
- Party wall awards with both adjoining owners
- Full tanking and waterproofing to BS 8102 with a guarantee
- Sump and pump systems with battery backup
- Natural light solutions — lightwells, sun pipes, glazed link
The standard we build to
Waterproofed to BS 8102 with a designed drainage system, and structurally designed by a chartered engineer with party wall awards in place before excavation begins.
Planning position
Almost always needs planning permission in Hammersmith & Fulham, plus party wall awards with both neighbours.
| Guide range | £2,500/m² |
| Typical duration | 4–9 months depending on excavation |
| Planning | Hammersmith & Fulham |
Guide ranges for budgeting, excluding VAT and professional fees. We quote a fixed price after a site visit.
Get a fixed priceBasements — what people ask
How much does a basement conversion cost in Fulham?
Converting an existing cellar — lowering the floor slightly, tanking and fitting out — is £2,500 to £4,000 per square metre. Excavating a new basement beneath the house, which means underpinning the existing foundations, is £4,500 to £7,000 per square metre. For a 40m² space that is roughly £100,000–£160,000 for a conversion against £180,000–£280,000 for a new dig.
Read the full answerDo I need planning permission for a basement in Fulham?
Almost certainly. Hammersmith and Fulham has a specific basement development policy that restricts depth, footprint and construction methods, and it applies more tightly in conservation areas. You will also need a Basement Impact Assessment in most cases. This is the one service where the planning position, not the build cost, decides whether the project happens.
Read the full answerWill a basement conversion cause damp?
Not if it is waterproofed properly. Below-ground rooms need a designed system to BS 8102 — typically a cavity drain membrane feeding a sump and twin pumps with battery backup, not just a tanking slurry. The failures you read about are nearly always single-layer systems with no drainage and no pump maintenance. We specify and guarantee the full system.
Read the full answerBasements across south west London
The housing stock and the planning authority change what is achievable. Each area page covers what is specific to it.
Planning basements in Fulham?
Tell us what you have in mind and we will come back with an honest view on cost, timescale and what is achievable at your address.