Harpenden house extensions
From a small utility to a two-storey addition, we take on house extensions throughout Harpenden, starting with a free visit and a planning check.
- Postcode districtsAL5
- Price regionEast of England (×1.06)
- Planning rulesEngland
- Site visitFree, no obligation
Planning and building control in Harpenden
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 England a two-storey rear extension is permitted development only if it projects no more than 3 m from the original rear wall, sits at least 7 m from the rear boundary, matches the roof pitch and uses obscure, non-opening side windows upstairs. Most two-storey extensions therefore go through a householder planning application, which costs £548 from 1 April 2026 and normally takes about 8 weeks.
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.
Applications are decided by the local planning authority (your district, borough or unitary council).
Popular extension prices in Harpenden
We publish guide prices so you can budget before anyone visits. For Harpenden they are adjusted by ×1.06, the factor we use across East of England.
| Extension type | Example size | Standard spec (inc VAT) |
|---|---|---|
| Extensions over a garage | 12 m² | £26,500 – £34,500 |
| Orangery extensions | 16 m² | £47,000 – £59,500 |
| Wraparound extensions | 25 m² | £60,500 – £77,000 |
| Side return extensions | 11 m² | £27,500 – £35,000 |
| Kitchen extensions | 20 m² | £44,500 – £56,500 |
| Double-storey extensions | 32 m² | £61,000 – £80,000 |
Areas we cover around Harpenden
Across AL5, we can visit, measure and advise. The same team covers St Albans (5 miles), Hemel Hempstead (6 miles), Welwyn Garden City (6 miles), Hatfield (7 miles), Stevenage (9 miles), all within easy reach. Luton, in Bedfordshire, is roughly 5 miles from Harpenden and also on our list.
What works best for Harpenden houses?
Across the East of England many houses sit on generous plots, and single-storey and wraparound extensions are a natural fit.
The types we would usually look at first for a home in Harpenden are double-storey extensions, bungalow extensions and wraparound extensions, depending on the garden and how the house is laid out.
All extension types we build in Harpenden
- Glass box extensions · from £31,500
- Annexe extensions · from £58,000
- Side return extensions · from £19,000
- Double-storey extensions · from £40,000
- Pitched roof extensions · from £23,500
- Single-storey rear extensions · from £22,000
- Flat roof extensions · from £22,000
- Side extensions · from £23,000
- Kitchen extensions · from £28,500
- Orangery extensions · from £31,500
- Planning permission for extensions · from £350
- Extension plans and drawings · from £1,250
- Bedroom extensions · from £27,500
- Timber frame extensions · from £22,000
- Home office extensions · from £16,500
- Building regulations for extensions · from £950
- Utility and boot room extensions · from £14,500
- Conservatory replacement extensions · from £21,000
- Bungalow extensions · from £27,500
- Porch extensions · from £4,200
- Wraparound extensions · from £38,000
- Extensions over a garage · from £25,000
Free site visit
A designer visits, takes measurements and photos, and discusses layouts, budget and timing with you.
Design and approvals
Once the layout is agreed, we deal with the council: planning permission or written confirmation that none is needed, plus building control.
Fixed written price
The price is fixed in writing once the design is settled, with a clear programme and payment stages.
Build and sign-off
We build it with one project manager, book the building control inspections and hand over the completion certificate.
Questions about extensions in Harpenden
How much does an extension cost in Harpenden?
Using our East of England factor (×1.06), a standard-spec single-storey extension of 20 m² is a guide £43,000 to £55,500 including VAT, and a 32 m² two-storey extension £61,000 to £80,000. Your written price follows the survey.
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 Harpenden?
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.
Who do I contract with?
Your contract is with S&K Property Investments and Improvement Ltd, which designs and manages the project and the build teams who carry it out.
Book a free site visit in Harpenden
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.