What 'outbuilding' means in planning terms
An outbuilding is typically a building within the curtilage of a house that is incidental to the enjoyment of the dwelling (e.g., garden storage, office, gym), not a separate home.
Planning Portal's outbuildings guidance frames them as permitted development subject to limits and conditions.
Permitted development rights for many householder projects do not apply equally across property types and locations; Planning Portal notes that house PD rights don't apply to flats/maisonettes and that designated areas have more restrictions.
Check if your property has full outbuilding PD rights.
PlanWiser's Property Checker shows conservation areas, Article 4 directions, and other constraints that restrict outbuilding rights.
Try it nowKey PD limits for outbuildings
Even where PD applies, you must stay within GPDO limits. Typical constraints include:
- Height limits (often 2.5m to eaves, 4m total for dual-pitch roofs; lower near boundaries)
- Position: not forward of the principal elevation
- Coverage: limits on how much of the garden can be covered by buildings
- Use: incidental to the dwelling—not a separate self-contained dwelling
When permission is usually required
Using the outbuilding as a separate dwelling: If the building becomes independent accommodation (especially self-contained with living/sleeping/cooking), it commonly triggers planning permission as a material change of use / creation of a new dwelling.
Designated land restrictions and removed PD rights: Planning Portal notes PD rights are more restricted in designated areas and different for listed buildings; government householder guidance warns rights can be removed via Article 4 or planning conditions.
Non-house properties: Flats/maisonettes generally do not benefit from the same householder PD rights.
When it may not be required
If you have a house (not a flat) and you meet the relevant PD limits and conditions, Planning Portal guidance indicates many outbuildings can be permitted development.
For certainty, an LDC can confirm lawfulness of proposed works as permitted development. This costs around £129 (half the full householder fee) and is useful for resale.
Planning a garden office or studio?
Describe your outbuilding to PlanWiser's AI Advisor and get instant guidance on whether you need permission and what limits apply.
Try it nowCommon expensive mistakes
These mistakes lead to enforcement or costly retrospective applications:
- Treating a garden building as a rental unit without checking planning status (high refusal/enforcement risk)
- Ignoring Article 4 directions or conditions removing PD rights
- Assuming the same rules apply to flats—they don't
- Building too tall or too close to boundaries and exceeding PD limits
Want proof your outbuilding is lawful?
Use PlanWiser's Mock Application tool to test your proposal, or get an LDC for formal certainty before you build.
Try it nowReal-world costs and timelines
LDC for proposed works: Around £129 (half the full householder fee) for formal proof.
Full planning application: If you need permission, expect around £258 for a typical householder application.
Decision times: 8 weeks for most applications (13 weeks for unusually large/complex).
Professional help: £1,500–£4,000+ if you need a consultant for a granny annexe or borderline case.
Step-by-step: what to do next
Follow this workflow:
- Confirm you have a house (not flat) and PD rights exist for the property
- Identify whether you're on designated land / special constraints using PlanWiser's Property Checker
- Design for incidental use and avoid features that make it an independent dwelling
- Apply for an LDC if you want proof
- Use PlanWiser's Planning Advisor and Mock Application tools to validate before building