A loft conversion adds a bedroom, bathroom, or office without extending your home's footprint. Costs vary significantly by conversion type, size, finish specification, and location.
Types of Loft Conversion
Roof light (Velux): Simplest, no roofline change, typically no planning permission needed
Dormer: Box extension projecting from roof slope, the most common UK type
Hip-to-gable: Converts sloping roof side to vertical gable, common on detached/end-of-terrace
Mansard: Full rear roof rebuild at near-vertical angle, most expensive and disruptive
| Type | Typical Cost (UK) | Planning Permission |
|---|---|---|
| Roof light / Velux | £15,000-£25,000 | Usually not needed |
| Dormer (rear) | £35,000-£60,000 | Often permitted development |
| Hip-to-gable | £45,000-£70,000 | Often needed |
| Mansard | £60,000-£100,000+ | Almost always needed |
What Pushes Costs Up
- Location: London and South East command 20-30% higher labour rates than the North
- Site access: Narrow streets and restricted gardens increase delivery and waste costs
- Existing roof condition: Older timber needing replacement can add thousands, rarely visible until work starts
- Adding a bathroom: Simple WC adds £3,000-£5,000; full bathroom adds £8,000-£15,000
- Specification level: Premium Velux windows, engineered floors, bespoke joinery all add to the total
Planning Permission and Building Regulations
Most rear dormer and roof light conversions fall within permitted development rights. However, conservation areas, listed buildings, and flats always require full planning permission regardless of type. Building regulations approval is always required regardless of planning permission status, covering structural integrity, fire safety, insulation, and staircase dimensions.
Return on Investment
A well-executed loft conversion typically adds 15-25% to property value, though this varies considerably by location and the quality of the finish. In high-value areas where space commands a real premium, the value uplift can exceed the full cost of the conversion — making it one of the few home improvements that can be genuinely profitable rather than purely a lifestyle upgrade.
The strongest returns consistently come from converting a loft into a bedroom with an en-suite bathroom, in an area where an extra bedroom commands a meaningful price premium on resale. In lower-value areas, or where the local market doesn't reward extra bedrooms strongly, the added value may not fully cover the conversion cost — in which case it's better to think of the work as a lifestyle investment for your own use rather than a guaranteed financial return.
A well-executed loft conversion typically adds 15-25% to property value, though this varies by location. In high-value areas where space commands a premium, the uplift can exceed the conversion cost. The strongest returns come from a bedroom with en-suite in an area where extra bedrooms add significant value.
Choosing a Contractor
Always obtain at least three written, itemised quotes before committing to a contractor, and make sure every quote covers an identical scope of work so you're genuinely comparing like for like rather than being misled by a low headline figure that excludes items another contractor has included. A quote that's notably cheaper than the others often signals excluded scope — perhaps no bathroom fittings, no flooring, or basic rather than upgraded Velux windows — rather than a genuinely better price for the same work.
Check that any contractor you're considering is a member of a relevant trade body such as the Federation of Master Builders, and ask specifically to see examples of completed loft conversions, ideally ones you can view in person or speak to the homeowner about directly. Confirm that the quote explicitly includes building regulations sign-off and, where required, planning permission handling, since chasing these separately after the fact can be both costly and time-consuming if they haven't been properly arranged from the outset.