Loft conversion cost by type
Typical all-in cost including build, insulation, staircase and finishing.
| Conversion type | What it is | Typical cost |
|---|---|---|
| Rooflight / Velux | Windows in existing roofline, no structural change | £25,000 to £40,000 |
| Dormer | Box extension out of the roof for headroom and space | £35,000 to £60,000 |
| Hip-to-gable | Extends a sloping side wall to vertical for more volume | £45,000 to £65,000 |
| Mansard | Rebuilds the roof to a near-vertical wall, maximum space | £50,000 to £75,000+ |
London and the South East sit at the top of these ranges; add for en-suites and high finishes.
What makes up the cost
How a typical dormer conversion budget breaks down.
| Element | Typical cost | Notes |
|---|---|---|
| Structural build | £20,000 to £40,000 | Steels, floor, roof and dormer construction |
| Staircase | £2,000 to £6,000 | New stairs and reconfigured landing |
| Insulation and plastering | £3,000 to £7,000 | Bringing the loft up to standard |
| Electrics and heating | £2,000 to £5,000 | New circuits, radiators and lighting |
| En-suite (optional) | £3,000 to £8,000 | Suite, tiling and plumbing |
| Windows and finishing | £2,000 to £6,000 | Rooflights, doors, decorating |
What affects the price
The main cost drivers for a loft conversion:
- Conversion type, rooflight is cheapest, mansard the most expensive.
- Roof structure, modern trussed roofs need more structural work than older cut roofs.
- Head height available, which determines what is feasible.
- Adding an en-suite or extra plumbing.
- Staircase position and any reconfiguration of the floor below.
- Location and access, and whether party wall agreements are needed.
Permissions and party walls
Many loft conversions fall under permitted development, but dormers to the front, larger volumes, and flats usually need planning permission. All conversions need building regulations approval, and terraced or semi-detached homes usually need a Party Wall Agreement with neighbours.
Does a loft conversion add value?
Lofts are among the best-return improvements, because:
- An extra bedroom, especially with an en-suite, can lift value significantly.
- It adds floor space without reducing the garden.
- It is usually cheaper per square metre than a ground-floor extension.
- Well-finished loft rooms are attractive to family buyers.
- Value added varies by area, so check local ceiling prices before over-spending.
Weigh a loft against buying bigger
A loft conversion is a major spend on top of your purchase. Our planner helps you set the full buying budget and reserve first, so you can see what is left for improvements like a loft before you commit.