Planning a home extension? For homeowners in a semi-detached property, understanding semi detached rear extension rules is essential before breaking ground. Whether you’re after a spacious kitchen-diner or a sun-soaked lounge, complying with UK regulations can save time, money, and neighbourly disputes.

What Counts as a Rear Extension?

A rear extension is any structure that projects beyond the rear wall of the original house. For semi-detached homes, these are typically built on the garden-facing side and can be single or double storey, depending on your needs.

Do I Need Planning Permission for a Semi Detached Rear Extension?

Permitted Development (PD) Rights

You can extend up to 3 metres without planning permission under PD rights. For larger builds:

• Up to 6 metres is possible via a prior approval application.

• PD does not apply if your property is in a conservation area, is listed, or is a flat or maisonette.

Key Rules to Follow for Rear Extensions

Height Restrictions

• • Must not exceed 4m in overall height.

  • If within 2m of a boundary, the eaves height cannot exceed 3m.

Depth Limitations

• • 3m without approval, or 6m with prior approval.

  • Two-storey extensions must not exceed 3m from the rear wall and must be at least 7m from the rear boundary.

Roof & Materials

• • Roof pitch must match the existing home.

  • Materials should be in keeping with the existing house to avoid refusal during planning.

Additional Considerations Before You Build

Party Wall Agreements

Sharing a wall with your neighbour? You’ll need to issue a party wall notice and possibly agree on a party wall award through surveyors if consent isn’t given.

Natural Light & Overshadowing

Ensure your design won’t negatively affect your neighbour’s right to light. Features like rooflights or glazed panels can bring in light while keeping the design neighbour-friendly.

Conservation Areas & Listed Properties

In protected zones, even minor extensions may require full planning permission, so always consult your local planning authority.

How Much Can a Rear Extension Add to My Home?

A well-designed rear extension can boost property value by up to 20%, particularly if it adds desirable spaces like an extra bedroom, bathroom or a modern kitchen.

Common Design Ideas for Semi Detached Rear Extensions

• • Open-plan kitchen-diners with bifold doors to the garden

  • Glass box extensions for a sleek, contemporary look

  • Utility rooms or playrooms to reduce indoor clutter

  • Double-storey extensions to add both living and sleeping space

Cost Expectations

• • Rear extensions typically cost between £1,500 to £3,500 per m², depending on materials and location.

  • London-based projects often lean toward the higher end.

Why Choose KT5 Construction?

At KT5 Construction, we specialise in cost-effective, regulation-compliant rear extensions tailored to your vision. Based in Surrey and London, we offer:

• • Clear communication and budget-conscious builds.

  • Expert guidance through party wall agreements, permitted development checks, and planning approvals.

Our experienced team understands the challenges homeowners face—from staying on budget to keeping peace with neighbours—and we’re here to guide you from concept to completion.

FAQ: Semi Detached Rear Extension Rules

1. Can I build a 6m rear extension without planning permission?

Only under prior approval, which still requires council submission and neighbour notification.

2. Do I need my neighbour’s permission to extend?

If you’re working near or on a shared wall, a Party Wall Agreement is required—even if planning permission isn’t.

3. Can I use different materials?

You can, but the design should be in keeping with the existing house to avoid planning issues or neighbour objections.

Call to Action

Ready to unlock the full potential of your semi-detached home? Contact KT5 Construction today for a free consultation. We’ll help you navigate the rules, manage costs, and bring your dream extension to life—on time and within budget.

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