Building
Extensions: When You Need Planning Permission and When You Don't
Most homeowners assume any extension needs planning permission. In reality, around 60% of the extensions we build go through Permitted Development — no full planning application needed, faster start, lower fees.
Here's how to tell which route applies to your project, accurate for England in 2026.
What Permitted Development actually allows
Under the General Permitted Development Order, a semi-detached or detached house can extend without full planning permission within these limits:
- Single-storey rear: up to 6m for semi/terrace, 8m for detached, max 4m height, max half the garden width
- Side extension: single-storey only, max 4m high, max half the original house width
- Two-storey rear: up to 3m projection, min 7m from rear boundary, matching roof pitch
- Materials: must be similar appearance to the existing house
What disqualifies you from PD
Permitted Development is removed in:
- Conservation areas (parts of Bishop's Stortford, Saffron Walden, Sawbridgeworth)
- Areas of Outstanding Natural Beauty
- Listed buildings (always need Listed Building Consent)
- Properties where PD rights have been removed by an Article 4 direction
- Any house created from a flat conversion or originally a maisonette
The Larger Home Extension scheme (Prior Approval)
Single-storey rear extensions between 4–6m (semi/terrace) or 4–8m (detached) need Prior Approval — a lighter-touch process than full planning. Council notifies neighbours; if no objections within 21 days, you're approved. Takes 6–8 weeks total.
When you definitely need full planning
- Two-storey extensions exceeding PD limits
- Anything in a Conservation Area or AONB
- Side extensions on a corner plot facing a highway
- Any extension on a Listed Building (also needs LBC)
- Building over the boundary or close to a public right of way
Full planning takes 8–13 weeks in our local councils (East Herts, Uttlesford, Epping Forest) and costs £258 in application fees.
Building Regulations apply either way
Critically — even if you don't need planning, you still need Building Regulations approval. This covers structural, thermal, fire and ventilation compliance. As CRC-certified contractors we can self-certify most elements and coordinate the building inspector for you.
What we handle for you
On every extension project we manage:
- Initial planning route assessment (free, on-site)
- Architect introduction or working from your existing drawings
- Planning or Prior Approval submission
- Structural engineer coordination
- Building Regulations submission and inspector liaison
- Party Wall agreements where needed
- Full build through to handover
Realistic timeline 2026
From first conversation to keys-in-hand on a typical single-storey rear extension under PD: 4–6 months. Two-storey under full planning: 7–10 months. We give you a Gantt chart on day one so you can see exactly what's happening when.
FAQs
Frequently asked questions
Thinking about an extension? Start with a free planning chat.
We'll visit your home, tell you straight whether your project is PD, Prior Approval or full planning — and what realistic costs and timelines look like.
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