Semi-detached rear extension

Rear extensions for semi-detached houses

Semi-detached houses are among the easiest homes to extend at the back: side access makes building simpler, one party wall instead of two keeps neighbour matters manageable, and the typical 1930s or post-war semi has a garden deep enough for a 3 to 6 metre rear extension or a two-storey addition.

Get a guide price Call 0800 088 6341

Modest single-storey rear extension in red brick with white French doors on a semi-detached house

What works best on a semi-detached house?

A single-storey kitchen-diner across the full width is the usual starting point. Where the side passage is wide, a wraparound or a garage conversion can be combined with it. A two-storey rear extension makes sense when the house is short of bedrooms.

We check the attached neighbour's rear windows and any extension they already have, because the depth they have built affects how a deeper scheme is judged.

How much does a semi-detached rear extension cost?

Allow £1,900–£3,100 per square metre including VAT for a standard single-storey specification. A 3 m × 4 m extension typically comes to £23,000–£37,000, and a 4 m × 6 m extension to £45,500–£74,500.

Do you need planning permission?

In England a single-storey rear extension can often be built under permitted development: up to 3 metres beyond the original rear wall of an attached house, or 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres if any part is within 2 metres of a boundary.

England also has the larger home extension route: a single-storey rear extension of up to 6 metres on an attached house or 8 metres on a detached house, after prior approval from the council. The council notifies your neighbours and has 42 days to decide; the fee is £249 (£310 for applications made from 8 December 2026). The route is not available on designated land such as conservation areas.

Different rules in Wales, Scotland and Northern Ireland. The limits above are for England. Check your own house with our depth checker or read how far you can extend without planning.

What is included?

Full-width kitchen-diner design
Side access used for deliveries
Party wall notice to the attached neighbour
Single or two-storey options
Matching brick, render or pebbledash
Steel beam into the existing house
Doors and rooflights
Building control sign-off

Guide prices by region

Per square metre of new floor, including VAT, standard specification.

Region	Per m² inc VAT
London	£2,470–£4,030
South East England	£2,130–£3,470
East of England	£2,010–£3,290
South West England	£1,980–£3,220
West Midlands	£1,900–£3,100
East Midlands	£1,840–£3,010
North West England	£1,790–£2,910
Yorkshire and the Humber	£1,770–£2,880
North East England	£1,710–£2,790
Wales	£1,770–£2,880
Scotland	£1,800–£2,940
Northern Ireland	£1,650–£2,700

Book a free site visit

Tell us about the house and we'll call to arrange a free, no-obligation visit.

Postcode

What are you planning?

Your name

Phone

Anything we should know? (optional)

I’ve read the privacy notice. S&K Group Holdings Ltd will use my details to reply to this enquiry, and the building team for my area may receive them to arrange the visit.

FAQ

Semi-detached rear extension questions

How far can I extend a semi without planning?

3 metres under permitted development in England, or up to 6 metres with prior approval, outside designated land.

Can I match pebbledash or render?

Yes. Many semis are refinished with new render across the whole back elevation so old and new match.

Single or two-storey on a semi?

Two-storey if you need bedrooms, single-storey if you need a bigger kitchen. Planning risk is lower for single-storey.

What if my neighbour has already extended?

That can make a matching depth easier to justify. We measure theirs at the survey.

Do I need a party wall agreement?

Usually with the attached neighbour, in England and Wales.

How long does a semi extension take?

10 to 16 weeks on site for a single-storey extension.

Where