Do I Need Planning Permission for a Rear Extension in 2026?
For most homes, a single-storey rear extension is Permitted Development and needs no planning application — provided it stays within the depth, height and eaves limits set out below. Go deeper than the standard limits and you can still avoid full planning by using the Larger Home Extension prior-approval route (up to 6m on a terrace or semi, 8m on a detached house). Double-storey rear extensions, conservation areas and listed buildings are where full planning bites. This 2026 guide covers every threshold that decides the answer for your project.
Rear Extension Planning — At a Glance
✓ Permitted Development (no planning)
- Single-storey, 3m projection (terrace/semi)
- Single-storey, 4m projection (detached)
- Up to 6m / 8m via Larger Home Extension prior approval
- Max height 4m; eaves under 3m within 2m of a boundary
- Built in materials similar to the existing house
- No more than half the land around the original house covered
✗ Planning likely needed
- Double-storey rear extension beyond 3m
- Anything forward of the principal elevation
- Extension within a conservation area or Article 4 zone
- Any work on a listed building
- Height over 4m or eaves over 3m near a boundary
- Verandas, balconies or raised platforms
Rear Extension Depth & Height Limits
Rear extensions fall under Class A of Schedule 2, Part 1 of the GPDO. The thresholds that decide PD vs planning:
Measure from the original rear wall — the house as first built (or as it stood in 1948). Previous extensions count against your allowance. On designated land (conservation areas, AONBs, National Parks) the larger 6m/8m route is not available and side extensions lose PD entirely.
Going Deeper Without Full Planning
The Larger Home Extension scheme (made permanent in 2019) lets you build a single-storey rear extension up to 6m (terrace/semi) or 8m (detached) using a lighter-touch prior-approval application rather than full planning. The process:
- Submit a prior-approval application (fee GBP 120) with a site plan and drawings
- The council notifies adjoining neighbours for a 21-day comment period
- If no neighbour objects, the council issues prior approval; if they object, the council assesses the impact on amenity
- Decision due within 42 days — you cannot start until approval (or the deadline passes)
- Maximum height remains 4m; the extension must be single-storey
This route is not available on designated land. For double-storey or wraparound schemes see our full extension planning guide.
Party Wall, Boundaries & Building Regs
Even when your extension is Permitted Development, two other approvals usually apply. Building Regulations are always required — Building Control inspects foundations, structure, thermal performance, drainage and fire safety, with a council fee of around GBP 500 to GBP 1,000 and a completion certificate you will need to sell.
The Party Wall etc. Act 1996 is triggered when you excavate foundations within 3m of a neighbour or build on the boundary line — common for terraced and semi-detached homes. Serve notice at least 2 months before work starts. If a neighbour dissents you will appoint a party wall surveyor, typically GBP 1,000 to GBP 2,500.
Talk to Extension Builders Who Handle Planning
A vetted extension specialist will assess your scheme against PD limits, advise on the prior-approval route, and submit any LDC or planning application for you. BestBuilders matches you with up to 3 UK extension builders.
Rear Extension Planning Permission FAQs · 2026
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