Basement and cellar conversion cost
Conversion costs vary widely with the size and condition of your cellar, the waterproofing needed and the finish you want. Below are indicative ranges from published UK cost guides to help you plan. They are not quotes and they are not BasementBridge prices.
Indicative cost ranges
| Type of project | Indicative cost per m² (2026) |
|---|---|
| Converting an existing cellar | about £1,000 – £2,200 |
| Existing cellar needing waterproofing and some structural work | about £1,500 – £3,000 |
| Excavating a new basement or lowering the floor with underpinning | about £1,900 – £5,000+ |
Ranges compiled from published guides; sources differ and figures may exclude VAT, fees and contingency.
What drives the price
- Starting point: a dry, accessible cellar with good head height costs far less than one needing excavation.
- Waterproofing: drained systems with a sump and pump cost more than simple tanking but are commonly used for habitable rooms. See our waterproofing cost guide.
- Structural work: underpinning, steel beams or a new slab add significantly.
- Light and access: light wells, windows and a compliant staircase.
- Services and finishes: heating, ventilation, electrics, flooring and any kitchen or bathroom.
- Professional fees: structural engineer, Building Regulations and, where relevant, party wall surveyors.
Getting a reliable price
Only a survey can tell you what your cellar needs. Ask for a written, itemised quote that states the waterproofing design, what is excluded and how contingencies are handled. Read our cellar conversions guide for the wider process, or use the questionnaire to be matched with one independent specialist covering your area.
Indicative ranges drawn from published UK 2026 cost guides (Checkatrade, MyBuilder, ResiQuote, BestBuilders), accessed 21 October 2026. They are not quotes and are not BasementBridge prices. Your specialist will price your property after a survey.