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Cellar & Basement Conversion

Unlock valuable extra space in your London home. We turn damp, unused cellars into dry, usable rooms — with the waterproofing done right, so the room stays dry for the long term.

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More space, without moving house

In London, space is at a premium. Many period homes sit on top of a cellar that holds nothing more than storage and spiders. Converted properly, that space can become a bedroom, home office, gym, playroom or utility, and it adds real value to the property.

The difference between a conversion that lasts and one that fails is the waterproofing beneath the finishes. As specialists, we design and install the below-ground protection to BS 8102 before a single stud or sheet of plasterboard goes up.

First, we survey the cellar and identify how water enters. Next, we choose the right system. A habitable room usually needs a cavity drainage membrane, while a dry store may suit cementitious tanking. Finally, we hand over a dry, guaranteed shell for your builder or fit-out team.

Get the dry-out and waterproofing right, and the rest of the conversion follows with confidence. Because we focus on the waterproofing, we work alongside your architect, structural engineer and builder. You can read more on our basement waterproofing page.

Design comes into it, too. We work alongside your architect, structural engineer and builder, and we give them the waterproofing details they need. Therefore the design and the dry-out plan fit together from day one.

A dry room also needs air, since stale air brings back damp. We advise on heating and ventilation so that the new space stays fresh. In addition, a sump and pump can keep the space dry in a wet winter, which gives you peace of mind.

Popular conversions

  • Spare bedroom or guest suite
  • Home office or studio
  • Home gym, cinema or games room
  • Utility, laundry or plant room
  • Wine cellar or dry storage
  • Self-contained lower-ground flat

How a Conversion Works

The waterproofing comes first — everything else is built on a guaranteed dry base.
01

Survey & feasibility

We assess the cellar, headroom, water conditions and how you want to use the space, and advise on what's achievable.
02

Waterproofing design

We design a BS 8102 system — usually Type C cavity drainage, sometimes with tanking — as the dry foundation for the conversion.
03

Install & drain

Membranes, drainage, sump and pump are installed, and the space is battened and prepared for insulation and lining.
04

Finish-ready & guaranteed

You're left with a dry, decoratable room ready for fit-out, backed by written guarantees on the waterproofing.
Waterproofing First
BS 8102 dry base for the fit-out.
Free Survey
Written report and fixed quote.
Guaranteed
Warranty on the waterproofing.

Cellar Conversion FAQs

How much does a cellar conversion cost in London? +
Costs vary widely with size, headroom, water conditions and finish. A straightforward dry-out and waterproofing to create usable space is far cheaper than a full habitable conversion with drainage, insulation and fit-out. We provide a fixed written quotation after a free survey.
Do I need planning permission to convert my cellar? +
Converting an existing cellar to a habitable room is often permitted development, but changing its use, altering the external appearance or lowering the floor may require planning permission or building control approval. We'll advise on what's likely to apply to your project.
What waterproofing do I need before converting a cellar? +
A habitable basement needs a properly designed waterproofing system to BS 8102 — usually a Type C cavity drainage membrane, sometimes combined with tanking. Getting the waterproofing right is the single most important part of any conversion; everything else is built on top of it.
Can you handle the whole conversion? +
We deliver the waterproofing and structural drying works that form the core of any conversion — tanking, cavity drainage, sump and pump, and preparation for finishing. We can advise on and coordinate the fit-out so you get a dry, usable room without juggling multiple trades.

Cellar Conversion Across London

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Explore Your Conversion

Book a free survey and we'll tell you what is possible and what it will cost. There is no obligation, so you can decide while you compare options.

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