Do I Need Planning Permission for a Rear Extension?

Permitted Development vs Planning Permission

Do I Need Planning Permission for a Rear Extension? matters most when a homeowner is close to making a decision and does not want a vague quote, soft assumption, or missing line item to become an expensive problem later.

Many rear extensions fall under 'permitted development' — meaning no planning application needed.

Permitted Development Limits (2026)

Detached houses:

• Extend up to 8m from rear wall (single storey).
• Extend up to 3m from rear wall (double storey).
• Maximum height 4m (single storey).
• Maximum eaves height 3m.

Semi-detached/terraced:

• Extend up to 6m from rear wall (single storey).
• Extend up to 3m from rear wall (double storey).
• Same height limits.

When You WILL Need Planning

• Extending beyond these limits.
• Listed building.
• Conservation area.
• Article 4 direction in place.
• Flat or maisonette.
• Previous extensions used up allowance.
• Extending forward of principal elevation.

The Neighbour Consultation Scheme

For larger single storey extensions (up to 8m/6m), you must notify neighbours. If they object, your council decides.

My Advice

Even if you think it's permitted development: 1. Apply for a Lawful Development Certificate (£103). 2. Proves to future buyers it was legal. 3. Avoids arguments later.

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Not sure about your extension? [Get an independent review](/#get-started) from The Building Guys.

Next Step

If you want help applying this to your own project, use the right route below.

• Start with [Quick Review](/quick-review) if you want a fast first check.
• Use [Builder Quote Review](/builder-quote-review) if you already have a quote in hand.
• See the [Sample Report](/sample-report) if you want proof before you buy.

Frequently Asked Questions

Why does planning permission rear extension matter so much?

Because planning permission rear extension often sits right at the point where money, scope, and risk meet. If the paperwork is vague here, homeowners usually discover the problem after they have already committed.

Should I ask the builder more questions before I agree?

Yes. Clear builders should be able to explain what is included, what is excluded, and what assumptions sit behind the price.

Is a quick review enough?

Sometimes, yes. If you only need a first sense-check, start with [Quick Review](/quick-review). If you already have a proper quote or more serious concern, use [Builder Quote Review](/builder-quote-review).

What if I want proof before I buy?

Look at the [Sample Report](/sample-report). It shows the kind of clear, practical output we are aiming to give homeowners before they sign anything.

Practical Questions to Ask Before You Commit

When homeowners are dealing with planning permission rear extension, the safest move is usually to slow the decision down and ask a few direct questions in writing.

• What exactly is included in the current price?
• What assumptions are being made that could change later?
• Which items are still provisional, estimated, or allowance-based?
• What would trigger a variation or extra cost?
• What needs clarifying before any deposit or approval is given?

Short questions like these often reveal whether the paperwork is genuinely solid or simply looks tidy at first glance.

The Safer Way to Use This Advice

Use this article as a filter, not as a substitute for proper review. If the issue still feels unclear after reading, that is usually the sign that a real second opinion is worth getting.

A Final Word on Planning Permission Rear Extension

• Planning Permission Rear Extension is worth checking before you commit.
• A weak decision around planning permission rear extension usually gets more expensive later.
• Clear paperwork around planning permission rear extension protects the homeowner, not just the builder.
• If planning permission rear extension still feels vague, get a second opinion before money moves.