Wraparound extensions in Harpenden: design, approvals and build
Thinking about a wraparound extension for your Harpenden home? Start with a free site visit: we measure up, check what the council will allow and give you honest guide figures on the day.
- Guide price in HarpendenFrom £38,000 inc VAT
- PlanningUsually a householder application
- Build time14–20 weeks on site
- Postcode districtsAL5
Working in Harpenden
We cover Harpenden and the postcode districts AL5. Nearby, we also take on projects in St Albans (5 miles), Hemel Hempstead (6 miles), Welwyn Garden City (6 miles), Hatfield (7 miles).
The East of England mixes market-town terraces, inter-war semis and modern estates. Clay soils are common in parts of the region, which can affect foundation design.
What should I budget for a wraparound extension in Harpenden?
For Harpenden we adjust our national guide rates by ×1.06, the factor we use for East of England. Figures include VAT; your written quote after the survey replaces them.
Typical rates in Harpenden: £2,120 to £3,920 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| Compact L-shape 18 m² | £38,000 – £46,000 | £43,500 – £55,500 | £55,000 – £71,000 |
| Medium L-shape 25 m² | £53,000 – £64,000 | £60,500 – £77,000 | £76,500 – £98,500 |
| Large L-shape 32 m² | £67,500 – £81,500 | £78,000 – £98,500 | £98,000 – £126,000 |
Try the guide-price tool to see a range for your own size and finish.
What we take care of
- Party wall notice support (England and Wales)
- Foundations, drainage and any manhole relocation
- Full internal finish or kitchen-ready shell
- Structural design for the corner and openings
- Householder planning application
Do I need planning permission in Harpenden?
In England a wraparound extension is assessed as both a side and a rear extension, and the combination usually falls outside permitted development, so most need a householder planning application (£548 from 1 April 2026).
The planning position for a specific Harpenden address depends on its history and any designations, which is why we check it at the first visit.
Building over or within 3 m of a public sewer needs the water company's consent, usually through a build-over agreement, before the foundations go in.
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).
What happens next
Site visits are free and there is no obligation. Where drawings are needed, the design stage is priced in writing before it starts.
Free site visit
A designer visits, takes measurements and photos, and discusses layouts, budget and timing with you.
Design and approvals
We produce the drawings and structural design, and manage the approvals so they are in place before work starts.
Fixed written price
We confirm the build price in writing, based on the approved drawings and the finishes you have chosen.
Build and sign-off
We build it with one project manager, book the building control inspections and hand over the completion certificate.
Wraparound extension questions answered
Do you cover all of Harpenden?
Yes. We cover Harpenden and the surrounding parts of Hertfordshire. Site visits are free and there is no obligation.
Will my neighbours in Harpenden be involved?
If a planning application or prior approval is needed, the council notifies neighbours. If the work is on or near a shared boundary, party wall notices may also be needed.
Do I need building regulations approval in Harpenden?
Yes. Almost every extension needs it, whatever the planning route. We prepare the drawings and book the inspections.
How much does a wraparound extension cost?
Our guide range is about £2,120 to £3,920 per m² including VAT. A 25 m² standard-spec wraparound typically lands around £60,500 to £77,000 in Harpenden before design and council fees.
Do wraparound extensions need planning permission?
Usually, yes. In England the side element counts as a side extension and the rear element as a rear extension, and the combination normally falls outside permitted development. A householder application costs £548 in England from 1 April 2026.
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.