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.
How much does a dormer loft conversion cost in Trowbridge?
In Trowbridge, a dormer loft conversion typically costs £49,000–£69,500 for a typical rear dormer with en-suite, including VAT at 20% (standard rate). Prices in the South West sit near the national average for this kind of work, and the range for Trowbridge reflects that. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| A typical rear dormer with en-suite | £49,000–£69,500 |
| Higher specification | £69,500–£87,000 |
Your quote will depend mainly on:
- Fire safety upgrades to the existing house
- Staircase position
- En-suite or bathroom
- Dormer size and roof structure
For a figure based on your own measurements, try the guide price tool, then book a free home visit for a fixed quote.
Do you need planning permission for a dormer loft conversion in Trowbridge?
The approval route for Trowbridge is set by planning law in 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.
Where work involves a shared wall, building on the boundary, or digging foundations within 3 metres of a neighbour’s building and deeper than its foundations (or within 6 metres for deeper work), the Party Wall etc. Act 1996 applies and notices must be served before work starts.
We check this for your address before design work starts, so there are no surprises later.
What we handle
Handled as part of most dormer loft conversions:
- Building control completion certificate
- Measured survey and head-height check
- Insulation, plastering, electrics and plumbing
- Drawings and structural calculations
- Steel beams and new floor joists
- New staircase and fire-safe escape route
How long does it take?
Expect 6 to 9 weeks on site. Allow time beforehand for drawings and approvals, usually 6 to 12 weeks.
Building in Trowbridge
The South West mixes stone and render cottages with post-war and newer estates, and local materials matter more here when matching an extension.
Trowbridge sits in Wiltshire. We cover the whole of Trowbridge, including postcodes BA14.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Build and handover
Work follows the agreed programme, with inspections along the way and a completion certificate at the end.
Questions about dormer loft conversions in Trowbridge
How much does a dormer loft conversion cost in Trowbridge?
In Trowbridge, a dormer loft conversion typically costs £49,000–£69,500 for a typical rear dormer with en-suite, including VAT at 20% (standard rate). Your fixed price depends on the survey and drawings.
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.
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.
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.
Who approves a dormer loft conversion in Trowbridge?
Planning matters in Trowbridge go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.