Do I Need Planning Permission for a Two-Storey Rear Dormer in 2026?
A standard rear loft dormer is usually Permitted Development if it stays within 50m³ (40m³ terraced) and meets the design limits. But a genuine two-storey rear addition almost always needs full planning permission. Here is exactly how to tell the difference.
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Two-storey rear dormer planning at a glance
A roof-level rear dormer is usually Permitted Development; a two-storey rear addition is not.
- Rear loft dormer within 50m³ (40m³ terraced): usually Permitted Development
- On designated land (conservation area, AONB, National Park): planning permission required
- Genuine extra first-floor + loft storey at the rear: full planning permission required
- Householder application fee: £258 · Lawful Development Certificate: £103
Permitted Development does not apply to flats, maisonettes or listed buildings. Always confirm with your local planning authority before building.
Permitted Development limits for a rear dormer (2026)
To build a rear dormer without a planning application in England, every one of these must be true:
| Rule | Limit |
|---|---|
| Added roof volume — detached / semi | Max 50m³ |
| Added roof volume — terraced | Max 40m³ |
| Set-back from original eaves | At least 20cm |
| Height vs existing ridge | Must not exceed ridge |
| Principal (front) elevation | No forward extension |
| Side-facing windows | Obscure-glazed, fixed below 1.7m |
Break any single rule and the dormer needs a householder planning application. A two-storey rear addition exceeds these limits by definition because it adds floor area below the roof. Even when a rear dormer stays inside Permitted Development, Building Regulations approval is separate and always required: the new floor joists must be sized for a habitable room, the loft needs a protected escape route with a 30-minute fire-resisting stair enclosure and mains-linked alarms, and insulation must meet the current Part L standard. A genuine two-storey rear scheme is judged as an extension rather than roof works, so councils weigh overlooking, loss of light and the impact on neighbours before granting consent — the same amenity tests that decide a two-storey rear extension. Where any excavation or shared wall is involved you will also need to serve notice under the Party Wall etc. Act 1996. If you are still weighing a simple loft dormer against a larger build, our guides on dormer planning rules and getting planning permission for a loft conversion walk through the drawings, validation and roughly eight-week determination you should expect.
4 Situations That Always Need Planning Permission
Conservation areas & AONBs
Dormers are excluded from Permitted Development entirely on designated land. A full planning application is required, and councils often resist visible rear dormers.
Removed PD rights
Some councils use an Article 4 Direction to remove Permitted Development on certain streets. Check the Article 4 register for your address before designing.
Extra storey at the rear
Adding floor area at first-floor level as well as in the loft is a two-storey extension, not a dormer. It needs full householder planning and a Party Wall agreement.
No PD at all
Flats and maisonettes have no Permitted Development rights, and listed buildings also need Listed Building Consent. Both require a full application.
More 2026 Loft & Planning Guides
All planning guides →Rear Dormer Planning 2026
Full Permitted Development rules for a standard rear dormer.
Loft Planning 2026
When a loft conversion needs planning permission.
Dormer Loft Cost 2026
What a dormer loft conversion actually costs.
Two-Storey Extension Planning
Planning rules for a two-storey rear extension.