A loft conversion turns the roof space into habitable rooms. Common forms include rear dormers, hip-to-gable, mansard and velux-only conversions. Most are PD for houses but several constraints apply in London.
Loft conversions are permitted development for houses (not flats) under GPDO Schedule 2, Part 1, Class B, within strict volume and design limits.
London is different. Conservation area coverage, Article 4 directions and listed buildings are much more common in London than the national average, and any of them can remove the PD route. Use the address-level checker before you assume PD applies.
These are the national permitted development limits set by Schedule 2 of the GPDO. If your scheme stays within every rule and no local constraint removes PD, you will not need planning permission — but you may still want a Lawful Development Certificate to prove it.
| # | Rule |
|---|---|
| 1 | Maximum added volume 40 cubic metres for terraced houses, 50 cubic metres for detached and semi-detached. |
| 2 | No part of the extension above the highest part of the existing roof. |
| 3 | No extensions on the principal elevation fronting a highway. |
| 4 | Side-facing windows must be obscure-glazed and non-opening below 1.7m from floor level. |
| 5 | Materials must be similar in appearance to the existing house. |
| 6 | Hip-to-gable extensions are not permitted in conservation areas. |
| 7 | Dormers must be set back at least 20cm from the eaves. |
These are the common reasons a loft conversion loses the permitted development route in London and needs a full householder application instead.
Planning outcomes vary significantly by borough. Conservation area coverage is the single biggest driver — boroughs with heavy CA coverage tend to see more loft conversion proposals need a full application.
Check whether the property is a house (not a flat), not in a conservation area, and not covered by an Article 4 direction.
A designer will confirm added volume is under 40m³ (terraced) or 50m³ (semi/detached) and that dormers comply with set-back rules.
Although not required, an LDC gives legal certainty that the conversion is PD and is often requested by buyers' solicitors.
Submit either an LDC or a full householder application depending on whether PD is available.
Separately submit Building Regulations — required regardless of planning route.
London range; varies with specification and site.
Householder application fee (2026). LDC fee is £129.
Statutory target for householder applications.
Usually no — most loft conversions on houses are permitted development provided the added volume is within 40–50m³ and the dormer is on the rear slope. Conservation areas and Article 4 directions frequently remove these rights. Flats always need planning permission.
The added volume (including any previous roof extensions) must not exceed 40m³ for a terraced house or 50m³ for a semi-detached or detached house. The dormer must sit on the rear slope, be set back 20cm from the eaves, and not exceed the ridge height.
Generally no. Mansard conversions alter the entire roof form and typically exceed the 40/50m³ volume limit. They almost always need a full householder application and are often refused in conservation areas.
No — permitted development rights for loft conversions only apply to houses. Any loft conversion on a flat or maisonette requires full planning permission plus landlord/freeholder consent.
Yes, always. Even a velux-only loft conversion that is PD for planning needs Building Regulations approval covering structure, fire escape, insulation, and stairs. Most loft conversions also trigger a Party Wall notice to adjoining neighbours.
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