Basements · London
Basement & Cellar Conversions in London
In London, where you often can't build out or up, going down is the best way to add significant space. A basement conversion can create a family room, cinema, gym, guest suite or utility space.
When you can't build out or up, go down
Basement projects are specialist work. We coordinate structural engineers, waterproofing design and party wall agreements, and plan the build carefully to protect your home and your neighbours.
We'll advise on feasibility and planning before you commit to design costs.
What's included
- Structural engineering and underpinning
- Excavation and spoil removal
- Waterproofing system design and installation
- Drainage and pumps
- Lightwells, glazing and fire escape routes
- Ventilation, electrics, heating and finishing
- Party wall coordination, planning and building control
Options
Basement options
Cellar conversions
Turning an existing cellar into habitable space by lowering the floor and waterproofing.
Basement extensions
Excavating under the house and, where permitted, under part of the garden.
Lightwells
Bringing daylight into lower ground floors.
Our process
How your project runs
1. Free site visit
We look at the space, listen to what you want and talk through budget and options.
2. Design & approvals
Drawings, structural calculations, and planning or permitted development where needed.
3. Fixed quote & programme
An itemised price and a week-by-week schedule before anything starts.
4. The build
Managed by one project manager, with regular updates and stage sign-offs.
5. Handover
Final walk-round, snagging, building control completion certificate and all your paperwork.
FAQs
Frequently asked questions
Do basement conversions need planning permission?
Converting an existing cellar often doesn't. Excavating a new basement or adding lightwells usually does, and many London boroughs have specific basement policies.
Will I need a party wall agreement?
Almost always for a terraced or semi-detached house. We help you serve notices and work with the surveyors.
How long does a basement take?
A cellar conversion may take 10–16 weeks; a full new basement often 6–9 months or more.
Considering a basement?
Book a free feasibility visit to find out what's possible under your home.