Can I build a 4m extension without planning permission?

Yes, if your property is semi-detached or terraced and the extension meets all other PD conditions (height, boundary distance, curtilage coverage). Detached houses can extend up to 8m under the Larger Home Extension scheme.

Does a flat roof extension need planning permission?

Not specifically because of the flat roof. The roof type does not determine whether PD applies — it is the depth, height, and boundary conditions that matter. Most flat-roof rear extensions qualify as PD.

What happens if I build without planning permission and it is not PD?

The council can issue an enforcement notice requiring you to demolish the extension or apply for retrospective planning permission. This is why a Certificate of Lawfulness (proving PD compliance) is worth the £1,500 investment.

Do I need planning permission for a small rear extension?

Small rear extensions (under 4m depth, under 3m eaves, under 4m height) almost always fall under PD. The size alone does not determine the need for planning — designation (conservation area, listed building) is the deciding factor.

Do I Need Planning Permission for a Single Storey Extension?

Last verified 1 February 2026

The short answer: probably not. Most single-storey rear extensions fall under Permitted Development and do not need a planning application. But PD comes with strict conditions — break one and you need full planning permission.

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Permitted Development conditions for single-storey extensions

Your extension qualifies as PD if it meets ALL of these conditions: (1) Maximum depth of 4m from the original rear wall (semi-detached/terraced) or 8m (detached, subject to Prior Approval); (2) Maximum eaves height of 3m; (3) Maximum overall height of 4m; (4) Does not extend beyond the side wall of the original house facing a highway; (5) Single storey only; (6) Does not cover more than 50% of the curtilage; (7) Materials similar in appearance to the existing house.

When you DO need planning permission

You need a full planning application if: your extension exceeds PD depth limits, your property is in a conservation area (reduced PD rights for side extensions, cladding), your property is listed (Listed Building Consent required for ALL changes), the original planning permission removed PD rights (common on newer builds), or you have already extended under PD and reached the limits.

The Larger Home Extension scheme

Detached houses can extend up to 8m under the Larger Home Extension scheme (also known as Prior Approval or Neighbour Consultation). This is not automatic PD — you must apply to the council (free) and your neighbours have 21 days to comment. The council then decides within 42 days. If no objections and no issues, it is approved. This scheme does not apply in conservation areas, National Parks, or AONBs.

Certificate of Lawfulness: do you need one?

A Certificate of Lawfulness is not legally required to build under PD, but it is strongly recommended. It provides legal proof that your extension complied with PD rules at the time of construction. Without it, a future buyer's solicitor will raise questions that can delay or derail your sale. We handle the application for £1,500.

Common questions

Frequently asked questions

Related planning guides

Permitted Development Rights: Complete Guide 2026 Certificate of Lawfulness: When & Why You Need One Extensions in Conservation Areas: What You Can Build

Extension guides

Single Storey Rear Extension Side Return Extension Kitchen Extension

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Do you need planning permission for a single storey extension? PD rules, depth limits (4m/8m), height conditions, and when you DO need to apply. Clear guide.

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