House extensions in Hertfordshire
Looking to extend your home in Hertfordshire? Start here: extension types, guide prices for Hertfordshire, the planning rules that apply and how a project runs.
- Towns listed18
- Price regionEast of England (×1.06)
- Planning rulesEngland
- Postcode districts48
Towns we cover in Hertfordshire
Towns we cover here include Watford, Hemel Hempstead, Stevenage, St Albans.
Do extensions in Hertfordshire need planning permission?
In England a single-storey rear extension can usually go up to 3 m beyond the original rear wall of a semi-detached or terraced house, or 4 m on a detached house, without a planning application, provided it is no more than 4 m high, keeps eaves to 3 m within 2 m of a boundary and, with other buildings, covers no more than half the land around the original house. The larger home extension prior approval scheme raises those depths to 6 m and 8 m, with neighbours notified and a 42-day decision.
In a conservation area, national park, National Landscape, the Broads or a World Heritage Site the permitted development limits are tighter (no side or two-storey extensions without an application). Listed homes need listed building consent, and if permitted development rights have been removed, any extension needs an application.
Building regulations approval is separate from planning. In England you can use the council's building control team or a registered building control approver; a full plans application gets the drawings checked before work starts, and the inspector signs the work off with a completion certificate.
What works best for Hertfordshire houses?
Across the East of England many houses sit on generous plots, and single-storey and wraparound extensions are a natural fit.
Depending on the plot, bungalow extensions and wraparound extensions are often the strongest options, with double-storey extensions worth considering where there is room.
What extensions cost in Hertfordshire
We publish guide prices so you can budget before anyone visits. For Hertfordshire they are adjusted by ×1.06, the factor we use across East of England.
| Extension type | Example size | Standard spec (inc VAT) |
|---|---|---|
| Conservatory replacement extensions | 14 m² | £31,500 – £41,000 |
| Wraparound extensions | 25 m² | £60,500 – £77,000 |
| Orangery extensions | 16 m² | £47,000 – £59,500 |
| Kitchen extensions | 20 m² | £44,500 – £56,500 |
| Side return extensions | 11 m² | £27,500 – £35,000 |
Extension types and starting prices
- Side extensions · from £23,000
- Wraparound extensions · from £38,000
- Orangery extensions · from £31,500
- Double-storey extensions · from £40,000
- Single-storey rear extensions · from £22,000
- Conservatory replacement extensions · from £21,000
- Building regulations for extensions · from £950
- Extensions over a garage · from £25,000
- Timber frame extensions · from £22,000
- Bedroom extensions · from £27,500
- Utility and boot room extensions · from £14,500
- Porch extensions · from £4,200
- Annexe extensions · from £58,000
- Home office extensions · from £16,500
- Planning permission for extensions · from £350
- Pitched roof extensions · from £23,500
- Flat roof extensions · from £22,000
- Kitchen extensions · from £28,500
- Bungalow extensions · from £27,500
- Side return extensions · from £19,000
- Extension plans and drawings · from £1,250
- Glass box extensions · from £31,500
Neighbouring areas
Questions about extensions in Hertfordshire
How much does an extension cost in Hertfordshire?
With our East of England factor (×1.06), a standard-spec 20 m² single-storey extension is a guide £43,000 to £55,500 including VAT. Prices for every type are linked on this page.
Do you handle building regulations?
Yes. We prepare the drawings and calculations, submit them and book inspections, ending with a completion certificate.
How long does an extension take in Hertfordshire?
Usually 2 to 4 months of design and approvals, then 10 to 16 weeks on site for a single-storey extension or 16 to 24 weeks for two storeys.
Do I need planning permission for an extension in Hertfordshire?
Not always. It depends on the size, position and your property's history. Many single-storey rear extensions in England are permitted development or can use prior approval.
Book a free site visit in Hertfordshire
We will measure up, check the planning position and give you honest guide figures.
- Free, no-obligation site visit
- Planning route checked before you spend on drawings
- Written price once the design is agreed
- Building control sign-off at the end
Prefer to talk? Call 0800 088 6341 or .
Book a free site visit
Tell us a little about the project and we will arrange a time.