Hertfordshire
Rear extensions for detached houses in Hertfordshire
Wider, deeper rear extensions with room for vaulted roofs and big glazing. Rear extensions in Hertfordshire: we cover 32 towns including Watford, Hemel Hempstead and Stevenage, with design, approvals and the build under one contract.
Detached houses in Hertfordshire often have room for a deeper rear extension under England's prior approval route or a full-width design. Hertfordshire mixes Victorian terraces with 1930s semis, so both side returns and full-width kitchen extensions suit houses here.
How much does a detached house rear extension cost in Hertfordshire?
Guide prices for a detached house rear extension in Hertfordshire start from our East of England rate of £2,070–£3,390 per square metre, including VAT. 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 |
|---|---|
| 4 m wide × 6 m deep (24 m²) | £49,500–£81,500 |
| 5 m wide × 8 m deep (40 m²) | £82,500–£135,500 |
These are guide ranges; the written quote after the survey is the figure that counts.
Do you need planning permission in Hertfordshire?
English permitted development (Class A) allows a single-storey rear extension of 3 metres on a terraced or semi-detached house and 4 metres on a detached one, measured from the original house, with a maximum height of 4 metres and eaves of no more than 3 metres within 2 metres of a boundary.
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.
England's rules allow a rear extension of more than one storey without an application only when it is no deeper than 3 metres and at least 7 metres from the boundary opposite the rear wall, and never on designated land. Most two-storey schemes need householder planning permission.
Conservation areas, National Parks, National Landscapes and the Broads restrict permitted development, and listed buildings always need listed building consent.
Where in Hertfordshire do we work?
- Watford
- Hemel Hempstead
- Stevenage
- St Albans
- Welwyn Garden City
- Cheshunt
- Hatfield
- Bishops Stortford
- Borehamwood
- Hitchin
- Hoddesdon
- Letchworth Garden City
- North Watford
- Harpenden
- Bushey
- Hertford
- Rickmansworth
- Potters Bar
- Berkhamsted
- Ware
- Enfield Lock
- Royston
- Croxley Green
- Broxbourne
- West Watford
- Batchworth
- Tring
- Chorleywood
- Codicote
- Baldock
- Abbots Langley
- Waltham Cross
FAQ
Questions people ask
How deep can I extend a detached house?
4 metres under permitted development in England, or 8 metres with prior approval, outside designated land.
Can I have a vaulted ceiling?
Yes, with a pitched roof and exposed or boxed rafters, subject to the height limits.
Is an oak frame worth it?
It is a premium finish with a long life; it costs more than blockwork with a plain roof.
Do you cover all of Hertfordshire?
We cover 32 towns and districts in Hertfordshire, including Watford, Hemel Hempstead and Stevenage.
Who builds the extension?
Vetted building teams working under contract to us; your contract is with S&K Property Investments and Improvement Ltd.