Planning guide · England & Wales

Permitted development: side extensions.

Single-storey side extensions can often be built under permitted development — but the rules are tighter than for rear extensions, especially on width and on the front of your home. Here is how it works in England and Wales, and how we get yours drawn and approved at a fixed price.

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A single-storey side extension with a mono-pitched glazed roof, built alongside a semi-detached red-brick house with a low brick front wall and block-paved driveway.

Does a side extension need planning permission?

Often not. A single-storey side extension can be permitted development in England and Wales — meaning no planning application — as long as it stays inside the size limits below. The rules are stricter than for rear extensions: the width and where it sits relative to the front of your home are what usually decide it. If any single limit is breached, or your home is on designated land, you need a householder planning application instead.

Yes, usually permitted development — a single-storey side extension no wider than half your original house, within the height limits.

No, you need planning permission — anything two storeys, wider than half the house, forward of the front wall, or on designated land.

Not sure which side of the line you’re on? We’ll check it for you as part of a free feasibility check — online, in about a minute.

Even when your side extension is permitted development, it almost always still needs building regulations approval for structure, insulation, drainage and fire safety. We handle both.

Permitted development limits, at a glance

Side extensions are treated more strictly than rear extensions. Here is how single-storey side extensions are dealt with in each nation.

England

Single-storey only: a two-storey side extension is not permitted development and needs full planning.
Width: no more than half the width of the original house.
Height: max 4m overall; eaves no higher than 3m within 2m of a boundary.
Position: must not extend forward of the principal (front) elevation; not permitted on designated land.

Wales

Single-storey only for permitted development, under Wales’ own order.
Width: generally no more than half the width of the original house.
Height: max 4m; the same close-to-boundary eaves rule applies.
Designated land & front-elevation restrictions apply — we confirm the position for your address.

A common one: the side-return extension on a Victorian terrace fills the gap beside the rear addition and is usually combined with a rear extension. The side-return part is often permitted development, but the combined footprint can tip you into the larger-extension or full-planning route — we assess the whole project, not just one wall.

How Arkiplan gets your side extension approved

We are an online architectural design service — the practical alternative to a traditional high-street architect. Our qualified design team draws your plans, works out whether you are permitted development or need a full application, and deals with the council on your behalf.

We confirm your route first. Permitted development, prior approval or full planning — we tell you which applies before you commit, so there are no surprises.
We scan, design and draw. A 3D Home Scan™ captures your home accurately, then we design with you on video and produce planning and building-regs drawings.
We submit and chase. We lodge the application, respond to officer queries and keep you posted — you get the decision notification in your pocket.
All at a fixed price. Agreed up front from your free design call — see our packages or how it works.

Side extension planning permission FAQ

Do I need planning permission for a side extension?

Not always. A single-storey side extension can be permitted development if it is no more than half the width of the original house, no taller than 4 metres, not forward of the front wall, and not on designated land. Two-storey side extensions, and anything outside those limits, need full planning permission.

How wide can a side extension be without planning permission?

Under permitted development, a side extension must be no more than half the width of the original house, and single-storey, with a maximum height of 4 metres. Anything wider or taller needs a full planning application.

Can I build a two-storey side extension under permitted development?

No. Two-storey side extensions are not covered by permitted development and require a full planning application in both England and Wales.

What is a side-return extension?

It is a single-storey extension that fills the narrow gap to the side of the original rear addition, common on Victorian and Edwardian terraces. It is often permitted development on its own, but is usually combined with a rear extension, so we assess the whole footprint.

Do I still need building regulations approval?

Yes. Planning rules decide whether you can build; building regulations govern how it is built. Almost every side extension needs building regulations approval regardless of whether it needed planning permission.

What if I live in a conservation area?

Permitted development rights for side extensions are usually removed on designated land such as conservation areas, national parks and AONBs, so a full planning application is normally required. We confirm the position for your specific address.

Start your side extension.

Fixed price, tailored to your project and confirmed in writing after your design meeting, with the planning route confirmed for your address.

Estimate my build cost→ Generate my free renovation report→ Check my project feasibility→ See what value it’ll add→ Instant design quote→ Do I need planning permission?→

All free, all online, all in about a minute — no obligation and no card needed.

Book a free design call

This guide is general information, not planning advice, and permitted development rules change and depend on your specific property and local authority. We confirm the current position for your address as part of every project.