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 Sidcup?
In Sidcup, a dormer loft conversion typically costs £62,500–£88,500 for a typical rear dormer with en-suite, including VAT at 20% (standard rate). We start from a UK-wide guide and adjust it for London, where labour and materials are typically about 30% above average. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| A typical rear dormer with en-suite | £62,500–£88,500 |
| Higher specification | £88,500–£110,500 |
The main things that change the cost:
- Fire safety upgrades to the existing house
- Staircase position
- En-suite or bathroom
- Scaffolding and access
Use the guide price tool to see how size and specification change the figure, then ask for a written, itemised quote.
Do you need planning permission for a dormer loft conversion in Sidcup?
Approvals for a dormer loft conversion in Sidcup follow the rules for 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.
Building regulations approval comes from the council’s building control service or a registered building control approver. The work is inspected at key stages, such as foundations, drainage and insulation, and a completion certificate is issued at the end.
We check this for your address before design work starts, so there are no surprises later.
What we handle
From survey to sign-off, the job normally involves:
- Party wall notices for shared walls
- Dormer structure, roof covering and windows
- Steel beams and new floor joists
- Drawings and structural calculations
- Insulation, plastering, electrics and plumbing
- New staircase and fire-safe escape route
How long does it take?
The build itself usually takes 6 to 9 weeks on site. Design and approvals come first and typically take 6 to 12 weeks, depending on the approval route.
Building in Sidcup
Victorian and Edwardian terraces dominate many London streets, which is why side return, wraparound and mansard projects are so common here.
If your home is in Sidcup or close by in Welling, Eltham and Bexleyheath, a free home visit is the first step.
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
Permissions sorted
Applications, building control and neighbour arrangements, all before the start date.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about dormer loft conversions in Sidcup
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.
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.
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.
How long does a dormer loft conversion take in Sidcup?
Typically 6 to 9 weeks on site. Design and approvals beforehand usually take 6 to 12 weeks.
How much does a dormer loft conversion cost in Sidcup?
In Sidcup, a dormer loft conversion typically costs £62,500–£88,500 for a typical rear dormer with en-suite, including VAT at 20% (standard rate). Your fixed price depends on the survey and drawings.