Letchworth Garden City, Hertfordshire
Semi-detached rear extension in Letchworth Garden City
Semi-detached rear extension in Letchworth Garden City: single or two-storey extensions for semi-detached houses, with side access and one party wall. We measure the house, show you what the rules allow, price it in writing and build it.
Letchworth Garden City and its postcode districts SG5, SG6 and SG7 are part of our Hertfordshire coverage. Where a Letchworth Garden City semi already has a small lean-to at the back, we usually replace it rather than extend it.
Book a free site visit
Tell us about the house and we'll call to arrange a free, no-obligation visit.
How much does a semi-detached rear extension cost in Letchworth Garden City?
A semi-detached rear extension in Letchworth Garden City is priced at £2,010–£3,290 per square metre including VAT as a guide, before kitchen fit-out and fees. East of England prices run slightly above our West Midlands baseline; clay soils near trees are the main foundation variable.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £24,000–£39,500 |
| 4 m wide × 5 m deep (20 m²) | £40,500–£65,500 |
| 4 m wide × 6 m deep (24 m²) | £48,500–£79,000 |
These are guide ranges; the written quote after the survey is the figure that counts.
Do you need planning permission for a semi-detached rear extension in Letchworth Garden City?
Here is how the rules in England apply to a semi-detached rear extension in Letchworth Garden City.
Under England's householder permitted development rules you can usually add 3 metres at the back of an attached house, or 4 metres on a detached house, without a planning application, as long as the extension stays under 4 metres high and its eaves stay under 3 metres where it is within 2 metres of a boundary.
A two-storey rear extension can be permitted development in England only if it projects no more than 3 metres, stays at least 7 metres from the rear boundary, matches the existing roof pitch and has obscure-glazed upper side windows. In practice most double-storey rear extensions go through a householder planning application.
If 3 or 4 metres is not enough, England's prior approval route allows 6 metres on a terraced or semi-detached house and 8 metres on a detached house for a single-storey rear extension. Neighbours are consulted, the council decides within 42 days, and the fee is £249, rising to £310 from 8 December 2026.
Conservation areas, National Parks, National Landscapes and the Broads restrict permitted development, and listed buildings always need listed building consent. We check your house's planning history and any conservation area before drawing, so the route is clear before you spend on plans.
What are homes in Letchworth Garden City like to extend?
Post-war semis and newer estates are typical of Letchworth Garden City, and many have room for a full-width extension. Shrinkable clay is common in the East of England, so foundations near trees and hedges are designed to NHBC-style depth guidance.
How a semi-detached rear extension in Letchworth Garden City comes together
Survey visit
We visit free of charge, measure up, check access, drainage and neighbours' extensions, and note what you want the room to do.
Options and costs
We draw layout options and price each one, so the budget shapes the design rather than surprising you later.
Approvals
Permitted development check, prior approval or planning application, then Building Regulations drawings and structural calculations, plus party wall notices where they apply.
Written price, then build
Once the design and approvals are in place, you get a fixed written price and programme, and we build through to sign-off.
Semi-detached rear extensions near Letchworth Garden City
From Letchworth Garden City, the nearest places we also cover are Baldock (1.7 miles) and Hitchin (3.2 miles).
- Semi-detached rear extension in Baldock
- Semi-detached rear extension in Hitchin
- Semi-detached rear extension in Henlow
- Semi-detached rear extension in Stevenage
- Semi-detached rear extension in Biggleswade
Other work in Letchworth Garden City:
FAQ
Semi-detached rear extension questions in Letchworth Garden City
What postcode areas do you cover around Letchworth Garden City?
Including SG5, SG6 and SG7, and the surrounding Hertfordshire area.
Can I get a price without a visit?
Our online guide-price tool gives a range in a couple of minutes. A written price needs a survey.
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.
Can you match the brick or stone on my Letchworth Garden City house?
We source the closest match and show you samples before ordering; reclaimed materials are often the best match on older houses.
Do I need planning permission for a rear extension in Letchworth Garden City?
Often not for a single-storey rear extension of up to 3 metres (4 metres on a detached house) under permitted development, or up to 6 or 8 metres with prior approval, unless the house is in a conservation area or its rights have been removed.
Do you handle building control in Letchworth Garden City?
Yes. We apply to the council or a registered building control approver and hand over the completion certificate.