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Cellar conversion cost: what it really costs in 2026
Per m², from dry storage to living space.
£1,500 – £3,750 /m²
Waterproofing an existing cellar starts around £1,500/m². Making it habitable runs about £2,700/m², and full living space with natural light around £3,750/m².
Price by spec
| Option | What it means | Typical price |
|---|---|---|
| Waterproofed | Dry, usable storage | £1,500 /m² |
| Habitable | Insulated, heated, finished | £2,700 /m² |
| Full living space | Light wells, full spec | £3,750 /m² |
What actually happens
- Survey — head height, damp and structure assessed
- Tanking or cavity-drain waterproofing installed
- Floor lowered if head height demands it (the big cost)
- Insulation, first-fix electrics and heating
- Staircase improved; light wells cut if planned
- Plastering, flooring and decoration
Popular choices
Cavity drain membranes (over tanking)Light wells and pavement lightsUtility-and-snug combinations
Regulations to know
- Building regulations always apply — waterproofing, ventilation, escape routes and head height
- Lowering the floor usually means underpinning: structural engineer territory and Party Wall notices for terraces
- Planning permission only if you alter the outside (light wells at the front)
Tips from the trade
- Head height decides everything — under 2.2m and the floor must drop, which can double the budget
- Get a waterproofing guarantee backed by insurance, not just the installer's word
Plan this project properly
Get a region-adjusted estimate, track budget against real quotes, and find local tradespeople -- free to browse on Qome.
Start planning on QomePrices on this page are approximate, region-adjusted guide figures built from cross-checked UK cost data. They exist to inform you, not to bind anyone. Actual prices are whatever you and your tradesperson agree, and a difference between a Qome guide figure and a real quote is not a fault in either.