The conversion guide / rear dormer
Rear Dormer Loft Conversions
Maximise headroom and floor space with a full-width rear dormer — the most popular loft conversion for terraced and semi-detached homes.
At a glance / 01
Terraced and semi-detached homes
The roofline / 02
A new rear-facing wall and flat roof replace part of the rear slope, bringing full standing height much further across the loft.
Planning / 03
A rear dormer may qualify under permitted development on a house if the design meets Class B conditions and those rights remain in place.
Find your fit
Is this the right conversion for your home?
More room where the roof used to slope. A practical way to make the most of a terraced or semi-detached house with a suitable rear roof slope. The existing roof and available height still need assessing.
A rear dormer loft conversion adds a large flat-roofed extension across the rear pitch of your roof. It's the most efficient way to unlock a full new floor of usable, headroom-rich space.
Concept Lofts specialise in full rear dormers finished to a premium standard — bespoke joinery, en-suites, walk-in wardrobes and floor-to-ceiling glazing where suitable.
It may suit
- Terraced and semi-detached homes
- Homes needing a full master suite with en-suite
- Properties where maximum head-height is critical
- Anyone wanting two additional bedrooms in the loft
Roof form / illustrationRoof anatomy
What happens to the roofline?
A new rear-facing wall and flat roof replace part of the rear slope, bringing full standing height much further across the loft.
Every roof is different. We survey the existing structure before recommending a design.
Built by Concept Lofts / North Weald
Real work. Real homes.
Full Rear Dormer Conversion – North Weald
Concept Lofts were able to extend this already beautiful house with the addition of a full rear dormer loft conversion.
View projectExplore dormer costs, designs and completed work in our specialist guide.
Read the full dormer guideThe planning route
Will I need planning permission?
Do I need planning permission for a rear dormer loft conversion? Many rear dormers on houses can be built under permitted development (PD), without a full householder planning application. The answer depends on the roof design, the house and any restrictions on its rights — not simply on the fact that the dormer is at the rear.
A full-width dormer still needs to fit the overall roof-space allowance and the detailed Class B design rules. We check earlier roof extensions too, even if a previous owner built them.
Class B / roof enlargement
The main checks, clearly set out.
For a house with roof-enlargement permitted development rights, the complete proposal must meet all relevant conditions:
Total additional roof space, including previous enlargements. These are limits, not automatic entitlements.
- 01
Additional roof space is generally limited to 40m³ for terraced houses or 50m³ for detached and semi-detached houses. Previous additions to the original roof count too, whoever built them.
- 02
The enlargement must not rise above the highest part of the existing roof or project beyond the plane of the existing roof slope on the principal elevation where it fronts a highway.
- 03
Exterior materials must be of a similar appearance to the existing dwellinghouse. This does not necessarily require the identical product: visible colour, design and overall finish should relate sympathetically to the house and roof.
- 04
The original eaves must normally be maintained or reinstated, with the nearest edge of the enlargement set back at least 0.2m from them so far as practicable. Relevant hip-to-gable work and enlargements joining the original roof to a side or rear extension have specific exceptions to this eaves rule.
- 05
The enlargement must not extend beyond the outside face of an original external wall, except where it joins the original roof to the roof of a side or rear extension. Minor roof details are treated separately.
- 06
Side-facing windows must be obscure glazed and non-opening unless their opening parts are more than 1.7m above the room floor. Verandas, projecting balconies and raised platforms are not permitted under Class B; a Juliet balcony without a platform can normally qualify if the other rules are met.
These are householder rights for houses, not an automatic route for flats or maisonettes. Class B roof-enlargement rights do not apply on designated land such as conservation areas, and rights can also be removed or restricted by an Article 4 direction or a condition on an earlier permission. Listed buildings have additional controls.
The dormer cheeks and front should have a finish similar in appearance to the existing house or roof. This need not be the identical product: colour, design and overall visual appearance matter.
A Juliet balcony without a projecting platform can normally be considered within PD if the other conditions are met; a projecting balcony or raised platform cannot.
Do I still need an application?
Even when full planning permission is not needed, we normally recommend applying for a Lawful Development Certificate (LDC) where appropriate. It formally confirms that the proposed work is lawful under permitted development. It is not planning permission and is not legally mandatory simply because work is PD, but it provides useful evidence for your records and a future sale.
We assess your property and loft design, check the relevant permitted development or planning route, prepare drawings and handle the appropriate council submission as part of our design and planning process. No approval can be guaranteed.
Planning and Building Regulations are separate. For more detail, read our loft conversion planning guide or the GOV.UK householder technical guidance. Rules here describe the general position for houses in England; the exact property and proposal must be checked.
Design decisions
The details make the difference.
The right materials, glazing and internal layout should feel like they belong to the home. Options are assessed against the design and any applicable planning conditions.
- 01Dormer cheeks and roof finish chosen to sit comfortably with the house
- 02French doors or a Juliet balcony where the design and rules allow
- 03Rooflights on the retained front slope for light over stairs or storage
Depending on the design, we can also discuss bespoke fitted wardrobes, en-suite shower rooms, juliet balconies & french doors, velux roof windows, solid oak stairs & glass balustrades.
From our North Weald project
Inside the roof
What could the space become?
A bedroom with a carefully planned en-suite, dressing area or built-in storage — the final layout depends on your roof and the position of the new stairs.
A measured survey and design consultation will establish what works in your home.
From first visit to finish
A considered route to a finished loft.
- 01 / 06
Assess
Survey the roof and establish whether rear dormer loft conversions suit the house.
- 02 / 06
Design
Develop the layout around a new rear-facing wall and flat roof replace part of the rear slope, bringing full standing height much further across the loft.
- 03 / 06
Planning / LDC
Check the permitted-development route and consider an LDC where appropriate.
- 04 / 06
Building Regulations
Coordinate structural design, stairs and technical approvals.
- 05 / 06
Build
Turn the agreed drawings into the finished space.
- 06 / 06
Completion
Finish the details and hand over the relevant certificates.
Good questions
Rear Dormer Loft Conversions, explained.
How long does a rear dormer take?
A typical rear dormer conversion with Concept Lofts is completed in 5–6 weeks on site, depending on the specification.
Will I need planning permission for a rear dormer?
Many rear dormers to houses qualify as permitted development, but the roof-space allowance, position, design and any restrictions on the property's rights must all be checked. We assess the route for your own home rather than assuming permission is unnecessary.
Explore another approach
A place to start
Could this be the right conversion for your home?
Tell us about your house. We’ll look at the roof, talk through your plans and advise on a sensible route forward.
Get a free loft assessmentBook a free consultation for your rear dormer loft conversions
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