Cowes, Isle of Wight
Semi-detached rear extension in Cowes
Thinking about a semi-detached rear extension in Cowes? Single or two-storey extensions for semi-detached houses, with side access and one party wall. Our team handles the drawings, the planning route and the build, and your contract is with one company throughout.
Cowes and its postcode districts PO31 are part of our Isle of Wight coverage. Where a Cowes semi already has a small lean-to at the back, we usually replace it rather than extend it.
Ask about a site visit
Visits here are by arrangement; we'll confirm before booking.
Cowes is outside our regular coverage, so visits and projects here are by arrangement: we confirm whether we can take the job, and agree any travel costs, before the first visit.
How much does a semi-detached rear extension cost in Cowes?
For Cowes we work from the South East England rate: £2,130–£3,470 per square metre of new floor, including VAT, standard specification. South East prices run above our West Midlands baseline, mainly on labour rates and clay-soil foundations.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £25,500–£41,500 |
| 4 m wide × 5 m deep (20 m²) | £42,500–£69,500 |
| 4 m wide × 6 m deep (24 m²) | £51,000–£83,500 |
Ground conditions, glazing, the roof and how far the house is opened up move the final figure within the range.
Do you need planning permission for a semi-detached rear extension in Cowes?
Whether your semi-detached rear extension in Cowes needs a planning application depends on its size, your house and any local restrictions.
In England a single-storey rear extension can often be built under permitted development: up to 3 metres beyond the original rear wall of an attached house, or 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres if any part is within 2 metres of a boundary.
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.
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.
Conservation areas, National Parks, National Landscapes and the Broads restrict permitted development, and listed buildings always need listed building consent. At the first visit we measure what is there now and tell you which route fits: permitted development, prior approval or a planning application.
What are homes in Cowes like to extend?
Cowes has a mix of Victorian terraces near the centre and larger Edwardian and inter-war houses further out. Clay soils across much of the South East mean deeper foundations near trees, which we plan for at the survey.
How a semi-detached rear extension in Cowes comes together
Look round and measure
We see the back of the house, measure it, check the drains and boundaries and hear what you need.
Options and costs
We draw layout options and price each one, so the budget shapes the design rather than surprising you later.
Planning and regulations
We take the design through the right planning route, then produce the construction drawings and engineer's calculations for building control.
Fixed price and build
A written price for the agreed design, a start date and a named contact through the build, ending with the building control completion certificate.
Semi-detached rear extensions near Cowes
We also build rear extensions for semi-detached houses in nearby East Cowes (0.5 miles) and Newport (4.2 miles).
- Semi-detached rear extension in East Cowes
- Semi-detached rear extension in Newport
- Semi-detached rear extension in Ryde
- Semi-detached rear extension in Sandown
- Semi-detached rear extension in Shanklin
Other work in Cowes:
FAQ
Semi-detached rear extension questions in Cowes
How much does a semi-detached rear extension cost in Cowes?
As a guide, £2,130–£3,470 per square metre including VAT for a standard specification. For example, 3 m wide × 4 m deep (12 m²): about £25,500–£41,500 at that rate. Your written price follows the survey.
Do I need planning permission for a rear extension in Cowes?
Often not for a single-storey rear extension of up to 3 metres (4 metres on a detached house) under permitted development, or up to 6 or 8 metres with prior approval, unless the house is in a conservation area or its rights have been removed.
How long does a semi extension take?
10 to 16 weeks on site for a single-storey extension.
Do I need a party wall agreement?
In England, usually yes if the extension is on or near a shared boundary or the foundations are close to a neighbour's building. We serve the notices.
Will I need a structural engineer?
Yes for the beam over the new opening and usually the foundations; we arrange them and their calculations go to building control.
Is the site visit in Cowes free?
Visits here are by arrangement; we confirm whether we can take the job and agree any travel costs first.