Hertfordshire
Two-storey rear extensions in Hertfordshire
A larger kitchen downstairs and an extra bedroom or bathroom upstairs, under one roof. Across Hertfordshire we handle the whole rear extension: survey, drawings, the planning route, building control and the build. Towns we cover here include Watford, Hemel Hempstead and Stevenage.
In Hertfordshire we check the neighbours' rear windows first, because the upper floor is where most two-storey schemes win or lose planning. Post-war semis and newer estates are typical of Hertfordshire, 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 much does a two-storey rear extension cost in Hertfordshire?
In Hertfordshire, our guide for a two-storey rear extension is £1,910–£2,860 per square metre including VAT for a standard specification. 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 × 5 m footprint, two floors (30 m²) | £57,000–£86,000 |
| 4 m × 6 m footprint, two floors (48 m²) | £91,500–£137,500 |
Your written price follows a measured survey and an agreed design, so it reflects your house, not an average.
Do you need planning permission in Hertfordshire?
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.
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
Does a two-storey rear extension need planning permission?
Almost always. England and Northern Ireland allow 3 metres without an application only if at least 7 metres remains to the rear boundary; Wales and Scotland are similar or stricter.
Is two-storey cheaper per square metre than single-storey?
Usually yes, because the foundations and roof are shared across twice the floor area. The total cost is higher.
Can I add an en-suite upstairs?
Yes. We plan the soil pipe route early so the bathroom sits where drainage works without boxing through the room below.
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.