The four types, roughly what they cost
- Velux / rooflight — the cheapest. No roof structure change, just windows in the existing slope. Typically £25k–£40k.
- Dormer — a box extension out of the roof for headroom and floor area. The UK's most common. Typically £40k–£65k.
- Hip-to-gable — squares off a hipped roof end to gain volume, usually paired with a dormer. £45k–£75k.
- Mansard — rebuilds a whole roof slope near-vertical for maximum space. The most expensive and most likely to need planning. £60k–£90k+.
What gets left out of an opening quote
Headline loft quotes often exclude the things that make it habitable: a compliant staircase (and the floor space it eats on the storey below), structural steels, party-wall agreements with neighbours, building-control fees, and rerouting the boiler or water tank.
Always confirm whether the quote includes finishes (flooring, decoration, built-in storage) or just a watertight, plastered shell.
What moves the number most
- Region — London and the South East run materially above national average.
- Staircase position — a clean run is cheap; reconfiguring the floor below is not.
- Planning vs permitted development — most rear dormers are PD; mansards and front-facing changes usually aren't.
- En-suite — adding a bathroom up there means new soil routing.
Put a number on it
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