Cellar and basement conversions
An existing cellar can become a home office, bedroom, gym, playroom or utility space without extending your home's footprint. BasementBridge is an introduction service, not a builder. Online matching opens soon — until then email hello@basementbridge.co.uk. When open, with your consent we will share your project with one independent conversion specialist covering your area.
What a cellar conversion involves
Every project is different, but most conversions of an existing cellar include:
- Waterproofing designed for habitable use under BS 8102:2022, often a cavity drain membrane with a sump and pump
- Head height checks, and sometimes lowering the floor or underpinning
- Insulation, ventilation and heating so the room is comfortable and condensation-free
- Light and escape, such as light wells, windows or a protected route out in case of fire
- Electrics, plastering, flooring and a safe staircase
Regulations to check
Converting a cellar into a habitable room will normally need Building Regulations approval, covering areas such as fire safety and escape, ventilation, insulation, structure and stairs. Planning permission is not always needed for converting an existing cellar in a house, but it can be if you are excavating, adding a light well that changes the outside, creating a separate dwelling or living in a listed building or conservation area. Digging near a neighbour's foundations may involve the Party Wall etc. Act 1996. Always confirm with your local authority and a qualified professional; this page is general information, not advice for your property.
Existing cellar or new basement?
Converting a cellar you already have is usually far simpler than excavating a new basement. Excavation brings structural engineering, party wall matters and more disruption. Our questionnaire asks which you are considering so the specialist can prepare properly.
How much does a cellar conversion cost?
Published UK cost guides put existing cellar conversions roughly in the low thousands of pounds per square metre, with excavation costing considerably more. We have summarised the indicative ranges, and what drives them, in our basement conversion cost guide. These are not quotes.
Waterproofing comes first
The waterproofing system is the part of a conversion you cannot easily put right later. If your cellar is currently damp or takes on water, read our guide to water in your cellar and our basement waterproofing page before you plan finishes.
How BasementBridge helps
- Tell us about your cellar and what you want to use it for. It takes about two minutes.
- Give consent on the final step. Nothing is shared before then.
- One specialist gets in touch to discuss a survey. We do not sell your enquiry to several firms.
Our service is free to homeowners. Specialists pay us a fee for each introduction; you pay them only if you choose to go ahead. See how it works for how specialists are selected and how your data is handled.
Questions to ask a conversion specialist
- Have you converted cellars of a similar age and construction?
- Who designs the waterproofing, and to what standard?
- Will you handle Building Regulations, or do I need an architect or engineer?
- What guarantees apply to the waterproofing and the build?
- What is included in the quote, and what could be extra?