How Far Can You Extend Without Planning Permission Semi Detached?

In the UK, you can extend a semi-detached house without planning permission under permitted development rights, but there are strict limits on how far you can go. As of current rules, you can build a single-storey rear extension that extends up to 3 metres from the original rear wall of the house without needing full planning approval. However, if you use the larger home extension scheme, this limit can stretch to 6 metres, but only if you notify the council through the prior approval process.

This scheme allows bigger extensions without a full planning application, but you must inform neighbours and your local authority. If objections are raised or conditions aren’t met, permission could be refused.

So in short — yes, you can extend up to 3 metres without permission, and up to 6 metres with prior approval. Anything beyond that will need full planning consent.

Can I Build on Any Part of the House Without Permission?

No — you can’t just build anywhere on your property and expect to bypass planning rules. Permitted development rights are location-specific and use-specific. For example, while rear extensions are generally allowed under Class A of the General Permitted Development Order (GPDO), side extensions, roof extensions, and front alterations have tighter restrictions.

You cannot build:

• At the front of the house (facing a highway) under permitted development

• Within 2 metres of a boundary if the extension height exceeds 3 metres

• Above the existing ridge height for upward extensions without permission

• On listed buildings, or homes in conservation areas, National Parks, or AONBs without checking first

If you’ve already extended your home before, those earlier changes count toward your permitted limits. That includes conservatories, garages, or garden rooms — so your new extension might tip you over the threshold.

Understanding Permitted Development Rights and Class A of the GPDO

Permitted development rights are a set of planning rules that let homeowners make certain changes to their property without submitting a full planning application. For extensions, the relevant rule is Class A of the Town and Country Planning (General Permitted Development) (England) Order 2015, often referred to as Class A of the GPDO.

Class A allows you to build a rear or side extension, within set size and design limits. These rights are designed to reduce bureaucracy for minor developments — but they come with strict criteria. If your design doesn’t follow every detail, the build is no longer permitted development and you’ll need planning permission.

It’s also worth noting that Article 4 Directions can remove these rights in specific areas. Councils use Article 4 to preserve the look of historic or sensitive neighbourhoods, meaning even minor extensions can require full planning approval.

What Can You Build Without Planning Permission?

Here’s what you can generally build on a semi-detached home without planning permission — provided it complies with Class A:

• Single-storey rear extension up to 3 metres, or 6 metres with prior approval

• Side extension that’s no wider than half the width of the original house and no taller than 4 metres

• Loft conversion with up to 40m² of additional space, provided it doesn’t raise the roof height

• Outbuildings (like sheds or offices) that don’t take up more than 50% of your garden area

You can also add rooflights, solar panels, and make internal alterations, as long as they don’t affect the external appearance significantly or require structural changes.

However, combining multiple permitted developments on the same property can quickly lead to issues — especially if your house has already been extended or altered. Always consider the cumulative impact.

General Restrictions and Conditions for Extensions

Even if your project qualifies as permitted development, you still have to meet the conditions laid out in the GPDO. These include:

• Materials must be similar in appearance to the existing house

• The extension must not exceed the highest part of the roof

• The eaves height must not exceed 3 metres if within 2 metres of a boundary

• Overlooking, overshadowing, or loss of light can still be challenged by neighbours — and councils can take enforcement action if the extension causes harm

• Building Regulations approval is still required for most work — especially for structural changes, insulation, drainage, and electrics

And importantly, just because something doesn’t need planning permission doesn’t mean you can build without oversight. Compliance with both planning law and building control is essential.

If you're unsure whether your semi-detached home qualifies for permitted development — or how far you can actually extend — it’s always a good idea to contact your local planning authority. You can also apply for a Lawful Development Certificate to prove your extension was built legally if you want peace of mind.

Prior Approval ≠ No Rules

A lot of homeowners think the larger home extension scheme means free rein up to 6 metres at the rear of a semi-detached house. Not quite. Yes, it skips a full planning application, but it still requires prior approval through the council — which involves notifying your neighbours, giving them a chance to object, and waiting for the green light. If they object and your extension causes potential harm to their outlook, light, or privacy, the council can block it.

“Original House” Definition Trips People Up

The "original house" isn’t always what you see now — it’s how the house stood in 1948, or when it was built if later. Any extensions added after that count toward your permitted development limits. So if your home already has a rear extension or conservatory, that space eats into your allowance. You might only have a metre or two left before you hit the limit — even if the existing extension was done years ago.

You Can Lose Your Permitted Development Rights

In some cases, you may not have any permitted development rights at all. This is especially common with:

• New builds, where developers often restrict further changes through the planning approval

• Flats or maisonettes, which don’t have permitted development rights

• Homes in conservation areas or with Article 4 Directions, where councils remove the automatic rights to control development more tightly

If you’re in any of these categories, even small extensions will need planning permission.

Side Extensions: People Get This Wrong

You can build a side extension under permitted development, but only if it meets very strict limits:

• It must be single storey

• It must be no more than 4 metres high

• It must be no wider than half the width of the original house

Go even slightly over that — for example, if it wraps around the back or has a higher roof — and you’re into full planning permission territory.

Also, side extensions that fill in alleyways (typical in semi-detached homes) can raise problems with drainage, access, and fire safety, which means Building Regulations get involved too.

Height and Eaves Rules Are Crucial

People often focus on how far they can extend, but they forget about how high. Even a 3-metre rear extension can get you into trouble if:

• The roof is pitched and the eaves are too high

• It’s within 2 metres of your boundary and exceeds 3 metres at the eaves

• The materials don’t match the original house

These small details can technically disqualify your extension from permitted development — which opens you up to enforcement.

You Still Need Building Regulations

Planning and building control are two separate processes. Even if you don’t need planning permission, you almost always need Building Regulations approval for:

• Foundations

• Insulation

• Fire safety

• Drainage

• Structural work

• Electrical installations

Skipping this step can lead to major issues down the line — especially if you plan to sell your home. Surveyors will flag unapproved work, and mortgage lenders may pull back without proper documentation.

Final Thought         

Just because something is allowed under permitted development doesn’t mean you should go ahead without doing your homework. Councils can and do take action when extensions are built that slightly overstep the mark — and that includes ordering demolitions or forcing retrospective planning applications (which aren’t guaranteed to be approved).

The smartest move? Before you build, check with your local authority, and consider applying for a Lawful Development Certificate — it proves that your extension was legal at the time of construction and gives you solid protection for the future.