How Much Does a Loft Conversion Cost in the UK?
Velux, dormer, hip-to-gable and mansard — realistic 2026 costs, timelines and what to expect.
A loft conversion is one of the most cost-effective ways to add space to a UK home. It typically adds 15-20% to your property value and costs significantly less per square metre than an extension. But prices vary widely depending on the type of conversion, your location, and the current state of your loft.
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What is included in these prices
A typical loft conversion quote should cover structural work (steel beams, floor strengthening), staircase, insulation, plasterboarding, electrics, heating, fire safety compliance, building regulations sign-off, and basic decoration. It usually does not include bathroom fitting (if you want an en-suite), flooring finishes, or furniture.
Adding an en-suite
Most loft conversions include an en-suite bathroom. Budget £3,000 to £6,000 on top of the conversion cost for a compact shower room. This covers the shower enclosure, toilet, basin, tiling, plumbing and waste routing. Waste pipes from a loft bathroom usually need a macerator or long gravity run, which adds complexity.
Planning permission
Most loft conversions fall under permitted development and do not require planning permission, provided they meet certain conditions: the volume added must not exceed 40 cubic metres for terraced houses or 50 cubic metres for detached and semi-detached houses. The conversion must not extend higher than the existing roof ridge. Materials should be similar in appearance to the existing house.
Dormers on front-facing roof slopes usually do require planning permission. Mansard conversions almost always need planning permission because they significantly change the roof shape. All loft conversions need building regulations approval regardless of whether planning permission is required.
Timeline
A Velux conversion takes 4 to 6 weeks. A dormer takes 6 to 8 weeks. Hip-to-gable and mansard conversions take 8 to 12 weeks. Add 2 to 4 weeks for an en-suite bathroom. These timelines assume no major complications and good weather for the structural work phase.
Stop guessing. Get an actual estimate.
Our AI estimator gives you a full materials and labour breakdown for your specific project in under 60 seconds. Free, no signup needed.