Falmouth, Cornwall
Semi-detached rear extension in Falmouth
Single or two-storey extensions for semi-detached houses, with side access and one party wall. If you live in Falmouth and want to know what a semi-detached rear extension would cost and whether it needs planning, start with the online guide price or a free site visit.
Falmouth sits in Cornwall, with postcode districts including TR11. In Falmouth we measure the attached neighbour's extension at the survey, because it often sets the sensible depth for yours.
Book a free site visit
Tell us about the house and we'll call to arrange a free, no-obligation visit.
How much does a semi-detached rear extension cost in Falmouth?
For Falmouth we work from the South West England rate: £1,980–£3,220 per square metre of new floor, including VAT, standard specification. South West prices run slightly above our West Midlands baseline; natural stone to match the house is the main variable.
| Size | Guide price inc VAT |
|---|---|
| 3 m wide × 4 m deep (12 m²) | £23,500–£38,500 |
| 4 m wide × 5 m deep (20 m²) | £39,500–£64,500 |
| 4 m wide × 6 m deep (24 m²) | £47,500–£77,500 |
Your written price follows a measured survey and an agreed design, so it reflects your house, not an average.
Do you need planning permission for a semi-detached rear extension in Falmouth?
Whether your semi-detached rear extension in Falmouth needs a planning application depends on its size, your house and any local restrictions.
Under England's householder permitted development rules you can usually add 3 metres at the back of an attached house, or 4 metres on a detached house, without a planning application, as long as the extension stays under 4 metres high and its eaves stay under 3 metres where it 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.
England also has the larger home extension route: a single-storey rear extension of up to 6 metres on an attached house or 8 metres on a detached house, after prior approval from the council. The council notifies your neighbours and has 42 days to decide; the fee is £249 (£310 for applications made from 8 December 2026). The route is not available on designated land such as conservation areas.
Conservation areas, National Parks, National Landscapes and the Broads restrict permitted development, and listed buildings always need listed building consent. We check your house's planning history and any conservation area before drawing, so the route is clear before you spend on plans.
What are homes in Falmouth like to extend?
Falmouth has Victorian terraces nearer the centre and post-war semis on the edges. Sloping gardens are frequent, which affects floor levels and steps down to the patio.
How a semi-detached rear extension in Falmouth comes together
Survey visit
We visit free of charge, measure up, check access, drainage and neighbours' extensions, and note what you want the room to do.
Drawings and budget
Floor plans and elevations for the options, each with a guide price.
Approvals
Permitted development check, prior approval or planning application, then Building Regulations drawings and structural calculations, plus party wall notices where they apply.
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 Falmouth
Neighbouring places we cover include Truro (7.7 miles) and Redruth (8.7 miles).
- Semi-detached rear extension in Truro
- Semi-detached rear extension in Redruth
- Semi-detached rear extension in Helston
- Semi-detached rear extension in Camborne
- Semi-detached rear extension in Newquay
Other work in Falmouth:
FAQ
Semi-detached rear extension questions in Falmouth
How much does a semi-detached rear extension cost in Falmouth?
As a guide, £1,980–£3,220 per square metre including VAT for a standard specification. For example, 3 m wide × 4 m deep (12 m²): about £23,500–£38,500 at that rate. Your written price follows the survey.
Is the site visit in Falmouth free?
Yes. We visit, measure up and talk through the options with no cost and no obligation.
Single or two-storey on a semi?
Two-storey if you need bedrooms, single-storey if you need a bigger kitchen. Planning risk is lower for single-storey.
What postcode areas do you cover around Falmouth?
Including TR11, and the surrounding Cornwall area.
Can you match the brick or stone on my Falmouth house?
We source the closest match and show you samples before ordering; reclaimed materials are often the best match on older houses.
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.