The most economical route to more space in a London terrace: convert your existing coal cellar or cellar chamber into a fully waterproofed, habitable room, no full excavation required, warranted for 25 years.
35+ full refurbishments completed · Delta Registered Installers · Free site visit and written quote.
A cellar conversion takes the sub-floor chamber that already exists beneath your London home, the coal cellar, the vaulted brick chamber under the pavement, the low-ceiling space that has always been used for storage, and turns it into a fully waterproofed, ventilated, habitable room. Most London terraces have one. Most of them are wasted.
The design and build of an existing cellar into a habitable, building-control-signed floor: waterproofing, ceiling height optimisation (where possible), first- and second-fix trades, ventilation, lighting and finishes.
Homeowners with an existing cellar or vault beneath a Victorian or Edwardian home, looking for more space at a lower cost and shorter timescale than a full basement excavation.
When you want an additional room: utility, home office, wine store, gym, snug, second reception, without the cost and disruption of digging out the whole basement.
A cellar conversion is often the highest-return-per-pound work available on a London terrace. Modest cost, meaningful space, and, because the structure already exists, none of the excavation risk.
Every UHM project runs through the same structured stages. You'll always know what's happening next, who's doing it and when it completes.
A director surveys the existing cellar, checks headroom, damp readings and structural condition, and confirms what's achievable.
Layout, headroom strategy, waterproofing and ventilation designed together. Building control application submitted.
Delta membrane cavity drainage installed by Delta Registered Installers, drainage channels chased in, sump-and-pump commissioned.
Metal stud framing, MVHR, electrics, plumbing, floor build-up, plastering, joinery and finishes installed by our in-house trades.
Building control completion certificate issued, MVHR commissioned, 25-year waterproofing warranty provided.
The name 'cellar conversion' hides a wide range of quality. Here's what a properly executed London cellar conversion actually involves.
Habitable rooms need habitable ceiling heights. Where an existing cellar is short of headroom, we can lower the floor within the existing walls (using limited underpinning), remove a redundant slab, or optimise ceiling build-ups. Every option is site-specific, we survey and specify honestly.
We install Type C cavity drainage as standard, the most reliable and maintainable waterproofing for a converted cellar. The Delta membrane system creates a drained cavity behind an internal skin, with any water routed to a sump-and-pump. This is not a job for paint or slurry.
Wine stores, home offices, utility rooms, gyms, snugs, playrooms, secondary reception rooms, guest bedrooms with en-suite (where headroom allows), and self-contained annexes. What you build depends on headroom, layout and how you want your home to live.
Many London terraces have brick vaulted chambers extending under the pavement. Where planning and structural condition allow, these can be brought inside the waterproofed envelope, extending usable floor area beyond the original footprint of the home.
A cellar conversion is typically the cheapest way to add habitable square footage in a London terrace, no excavation, no full underpinning.
Because the shell already exists, most cellar conversions complete in a fraction of the time of a full basement excavation project.
The same Delta Registered warranty we provide on new basement conversions, cellars aren't lesser projects on our books.
Waterproofers, first-fix, second-fix and joinery all UHM staff. No handovers, no gaps, one accountable team.
Most cellar conversions can be delivered while the upper floors of the home remain fully occupied and functional.
Every UHM cellar conversion is delivered with building control sign-off and the completion certificate for your file.
Cellars are damp environments. Converting one without properly designed waterproofing, ventilation and headroom sequencing is how you take a working storage space and turn it into a leaking, musty, unusable room.
Painting or lining a cellar wall without cavity drainage traps moisture behind the finish. Within a year the plaster fails, the skirting rots and the room smells.
Building control expects habitable headroom, many old cellars need floor lowering or specialist ceiling detailing to reach it, and neither is a job to improvise on site.
A cellar with no MVHR or extract strategy accumulates humidity: condensation on cold walls, mould in corners and an unmistakable basement smell. All avoidable at design stage.
Painting waterproof paint onto damp brick and calling it 'tanked'.
Skipping cavity drainage because the cellar 'seems dry'.
Fitting timber studs directly against below-ground walls.
Ignoring building control approval because 'it's just a cellar'.
Installing plug sockets and lighting without proper electrical certification.
Not commissioning ventilation before finishing the room.
Straight answers we give on almost every free site visit, cost, timeline, guarantees and what's included.
Every project is priced per project, no fixed prices. Cellar conversions are typically the most economical basement-related project because the shell already exists, but the number depends on headroom strategy, waterproofing scope and finish level. Site visits and quotes are free.
Typically three to six months from start on site to handover, depending on whether floor lowering is required and the specification of the finish. Confirmed in the written quote.
Many cellar conversions fall under permitted development, but if you're changing the external appearance of the house or excavating below the pavement, planning permission may be needed. We can advise informally at survey stage.
Depends on your headroom, your budget and your ambition for the space. Cellar conversions are faster and cheaper; a full excavation adds a bigger floor with more headroom. We give an honest read at the site visit, not the biggest job we can sell.
Yes, provided it's delivered with building control sign-off, which every UHM conversion is. It also carries a 25-year waterproofing warranty, which buyers' surveyors look for.
Sometimes, we can lower floors or optimise ceiling build-ups to reach habitable heights. Where it's genuinely not feasible we'll say so at the survey.
In most cases, yes. Damp cellars are what Delta cavity drainage was designed for. We survey, specify the right system and design the ventilation. The finished room is dry, ventilated and warranted.
25-year waterproofing warranty (Delta Registered Installers), plus building control completion certificate and full documentation at handover.
A director will visit, survey the space, and give you a written specification and quote, for free. If it's not the right project for your home, we'll tell you.
