WHAT CAN YOU BUILD UNDER PERMITTED DEVELOPMENT?
A practical guide to extensions, lofts, garages and outbuildings — checked against current national guidance and updated September 2026.
Permitted development is useful — but it is not one simple rule.
Permitted development (PD) rights can allow certain work to a house without a full planning application, provided every relevant limitation and condition is met. The rules depend on the original house, previous extensions, location, boundaries, roof form and whether rights have been restricted.
This guide covers the national rules for houses in England. Flats and maisonettes do not benefit from the same householder PD rights. Planning conditions and Article 4 Directions can also remove or restrict rights locally.
Planning permission and Building Regulations are different.
A project may be permitted development and still require Building Regulations approval, structural calculations, a Party Wall process, drainage consent or other approvals.
For certainty that proposed work is lawful, a homeowner can apply to the local planning authority for a Lawful Development Certificate.
Extensions
Standard rear extension
Up to 3m beyond the original rear wall for an attached house, or 4m for a detached house, subject to the other Class A limits.
- Maximum overall height: 4m.
- If within 2m of a boundary, eaves height must not exceed 3m.
- Total extensions and outbuildings must stay within the 50% curtilage rule.
Up to 6m / 8m
On eligible houses outside Article 2(3) land and Sites of Special Scientific Interest, a single-storey rear extension may reach 6m for an attached house or 8m for a detached house.
This requires the Larger Home Extension prior approval / neighbour consultation process before work starts. The current national application fee is £249 (from 1 April 2026).
Single storey only
- Maximum height: 4m.
- Width cannot exceed half the width of the original house.
- Not permitted beyond a side wall on Article 2(3) land.
- A side extension that also projects to the rear must satisfy both side and rear limits.
Up to 3m rear projection
- Must not project more than 3m beyond the original rear wall.
- Must be at least 7m from the boundary opposite the rear wall.
- Side extensions of more than one storey require planning permission.
- Upper-floor side windows must be obscure glazed and restricted opening where required.
Loft conversions & roof alterations
40m³ / 50m³ allowance
Additional roof space is limited to 40m³ for terraced houses and 50m³ for semi-detached and detached houses. Previous roof enlargements count toward the allowance.
No projecting dormer to the principal highway elevation
A roof enlargement must not extend beyond the plane of an existing roof slope that forms the principal elevation and fronts a highway.
Stay below the existing highest roof point
The enlargement cannot exceed the highest part of the existing roof. Balconies, verandas and raised platforms are not permitted under Class B.
Privacy conditions apply
Side-elevation windows must be obscure glazed and non-opening unless the opening part is more than 1.7m above the room floor.
Class C
Rooflights can often be PD where they do not project more than 0.15m (150mm) beyond the original roof plane and do not rise above the highest part of the original roof.
Roof extensions restricted
Class B roof enlargements are not permitted development on Article 2(3) land such as conservation areas, National Parks, National Landscapes/AONBs, the Broads and World Heritage Sites.
Outbuildings, garden rooms & detached garages
2.5m near a boundary
If any part of the building is within 2m of a boundary, the overall height is limited to 2.5m.
Otherwise the maximum is generally 4m with a dual-pitched roof or 3m for another roof form, with a maximum eaves height of 2.5m.
Not in front of the principal elevation
Outbuildings are not PD on land forward of a wall forming the principal elevation of the original house.
Incidental use — not a separate home
Class E covers buildings for purposes incidental to the enjoyment of the house. It does not permit a separate self-contained dwelling or primary residential accommodation such as an independent bedroom, bathroom and kitchen arrangement.
The 50% rule applies
Extensions and other buildings together must not cover more than half the area of land around the original house, excluding the original house itself.
Internal garage conversions often do not need planning permission.
Planning permission is not usually required where the work is internal and does not enlarge the building. However, planning permission may be required where the garage becomes a separate dwelling, where external alterations fall outside PD rights, or where the property's rights have been restricted.
Garage conversions will commonly require Building Regulations approval for matters such as structure, insulation, ventilation, fire safety, drainage and electrical work.
Newer estates can be different.
Planning conditions sometimes remove garage-conversion PD rights, particularly on newer developments. Conservation status or listed building controls can also change the route.
Garage conversion servicePorches
All three limits need to be satisfied for the porch to fall within the standard householder permitted development right, subject to the usual property-specific restrictions.
Five checks we would make first.
Original house
Establish what is original and what has been added since 1 July 1948 or first construction.
Previous work
Earlier extensions and roof additions can use up permitted allowances.
Location
Check conservation area, National Landscape/AONB, National Park, World Heritage and SSSI constraints.
Restrictions
Check Article 4 Directions and planning conditions that may remove PD rights.
Other approvals
Confirm Building Regulations, structure, drainage, Party Wall and any other consents.
START WITH DBM DESIGN & TECHNICAL.
Send us the property details and what you want to build. We can discuss the likely planning route, prepare architectural drawings, coordinate structural engineering and move the project toward Building Regulations and a construction quotation.
Send your drawings, engineer's calculations and specification and DBM can review the construction side.
Send your drawings →Where this guide was checked.
This page is a homeowner summary, not legal or planning advice. The detailed rules remain the legislation and official national guidance. We checked this September 2026 update against GOV.UK's householder permitted development technical guidance and Planning Portal guidance for extensions, loft conversions, roofs, outbuildings, porches and garage conversions.
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