The four types, roughly what they cost
- Velux / rooflight: the cheapest. No roof structure change, just windows in the existing slope. Typically £25k to £40k.
- Dormer: a box extension out of the roof for headroom and floor area. The UK's most common. Typically £40k to £65k.
- Hip to gable: squares off a hipped roof end to gain volume, usually paired with a dormer. £45k to £75k.
- Mansard: rebuilds a whole roof slope near-vertical for maximum space. The most expensive and most likely to need planning. £60k to £90k+.
What gets left out of an opening quote
Headline loft quotes routinely 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, and the rewiring the new floor needs.
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.
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