What is a dormer loft conversion?
A dormer loft conversion adds a box-shaped structure to the rear roof slope, creating vertical walls and full headroom across most of the new room. It is the most common loft conversion in the UK because it works on terraced, semi-detached and detached houses.
A rear dormer is often permitted development, within roof volume limits. It typically fits a double bedroom with an en-suite, or two smaller rooms.
What we handle
- Measured survey and head-height check
- Drawings and structural calculations
- Party wall notices for shared walls
- Steel beams and new floor joists
- Dormer structure, roof covering and windows
- New staircase and fire-safe escape route
- Insulation, plastering, electrics and plumbing
- Building control completion certificate
Options to consider
Full-width rear dormer
Maximises space across the whole back of the roof.
L-shaped dormer
On a house with a back addition, two dormers joined to form an L.
En-suite bathroom
Plumbing is planned to connect to the existing soil stack.
Juliet balcony
Glazed doors with a guard rail; balconies and terraces need planning permission.
How much does a dormer loft conversion cost?
A dormer loft conversion typically costs £48,000–£68,000 for a typical rear dormer with en-suite across the UK, including VAT at 20% (standard rate). Build time is usually 6 to 9 weeks on site. Design, structural calculations and council fees are extra.
| Region | Guide range (for a typical rear dormer with en-suite) |
|---|---|
| London | £62,500–£88,500 |
| South East | £54,000–£76,000 |
| East of England | £51,000–£72,000 |
| South West | £49,000–£69,500 |
| West Midlands | £46,500–£66,000 |
| East Midlands | £45,500–£64,500 |
| North West | £45,000–£64,000 |
| Yorkshire and the Humber | £44,500–£63,000 |
| North East | £43,000–£61,000 |
| Wales | £44,000–£62,500 |
| Scotland | £46,500–£66,000 |
| Northern Ireland | £41,500–£58,500 |
What changes the price:
- Dormer size and roof structure
- En-suite or bathroom
- Staircase position
- Fire safety upgrades to the existing house
- Scaffolding and access
- Built-in storage and finishes
Use the guide price tool for a figure based on your measurements, or see all guide prices.
Do I need planning permission?
England
In England a rear dormer is often permitted development if the extra roof volume is no more than 40 cubic metres on a terraced house or 50 on other houses, it does not face the road, sits no higher than the ridge and is set back from the eaves, with matching materials and obscure-glazed side windows. Balconies, front dormers and work in conservation areas need planning permission.
Wales
In Wales roof enlargements such as rear dormers can be permitted development within volume limits and design conditions. Dormers facing a road, balconies and conservation-area work need permission.
Scotland
In Scotland a dormer is permitted development (Class 1D) only on a roof slope that does not face a road, at least 10 metres from the boundary it faces, no wider than half the roof at the eaves, set at least 0.3 metres from the roof edges and with no increase in ridge height. It is not permitted development in a conservation area, and a building warrant is needed for a loft conversion.
Northern Ireland
In Northern Ireland a rear dormer can be permitted development if it does not face a road, sits no higher than the ridge and is set back at least 0.5 metres from the ridge, eaves, party wall and verges. Roof enlargements are not permitted development in conservation areas.
Even when planning permission is not needed, building regulations approval (a building warrant in Scotland) usually is. We make the applications and book the inspections.
How long does it take?
Typically 6 to 9 weeks on site. Surveys, design and approvals usually take 6 to 12 weeks beforehand.
How it works
- 01
Free visit
We look at the property, discuss what you want and measure up.
- 02
Design and fixed quote
Drawings, calculations and an itemised price for the agreed specification.
- 03
Approvals
Planning or permitted development, building regulations and neighbour matters.
- 04
Build and sign-off
Built to a written programme, with a completion certificate at the end.
Dormer loft conversions: questions and answers
Does a dormer loft conversion need planning permission?
A rear dormer is often permitted development in England, provided the extra roof volume is within 40 cubic metres on a terraced house or 50 on a semi-detached or detached house, and it does not face the road. Front dormers and houses in conservation areas usually need an application.
How much head height do I need?
Ideally at least 2.2 metres from the top of the ceiling joists to the underside of the ridge. Less can still work with a dormer, but we check this at the survey.
What fire safety is required?
Building regulations require a safe escape route. Converting a two-storey house to three storeys usually means a protected stairway with fire doors to habitable rooms and mains-wired smoke alarms.
Will I need to move out?
No. Most of the work is done from scaffolding and the roof. The new staircase is formed near the end, which causes a few days of disruption.
Do I need a party wall agreement?
In England and Wales, if the conversion cuts into or builds on a shared wall, notices must be served under the Party Wall etc. Act 1996.
How long does it take?
Usually 6 to 9 weeks on site.