Extensions over a garage in St Austell
Thinking about an extension over a garage in St Austell? We design it, take it through the approvals it needs and build it, with one team responsible from the first visit to the final certificate.
What we'd confirm first for a project in St Austell.
- Postcode districts
- PL23, PL24, PL25 and PL26
- County / area
- Cornwall, England
- Price region
- South West England
- Guide price
- £32,500–£47,500 (£1,800–£2,630 per m²)
- Approval route
- Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.
- Nearest towns
- Bodmin (9.2 miles), Truro (13.5 miles), Newquay (14.1 miles)
- Distance to Truro
- about 13.5 miles
- First visit
- Free, no obligation
About an extension over a garage
An extension over a garage is a new first-floor room built on top of an existing attached garage, usually a bedroom, en-suite or study. It uses a footprint you already have, so it adds floor space without taking any garden. The garage walls and foundations often need strengthening or replacing to carry the new floor.
Around St Austell we also work in Bodmin, Truro and Newquay, and across the rest of Cornwall. Postcode districts in and near St Austell: PL23, PL24, PL25 and PL26.
What it costs in St Austell
Our guide for South West England is £1,800–£2,630 per m² including VAT. On a project with 3 m × 6 m of new first-floor space (18 m²), that puts an extension over a garage in St Austell at roughly £32,500–£47,500. Keep a contingency of around 10% for things nobody can see until the ground is opened up.
| Spec | Per m² | 3 m × 6 m of new first-floor space (18 m²) |
|---|---|---|
| Essential | £1,660–£2,420 per m² | £30,000–£43,500 |
| Standard | £1,800–£2,630 per m² | £32,500–£47,500 |
| Premium | £2,160–£3,150 per m² | £39,000–£56,500 |
Planning and building regulations in St Austell
In England, most garages sit beside the house, so building over one makes a two-storey extension beyond a side wall, which always needs planning permission. If the garage is at the rear, the 3 m and 7 m rules for two-storey rear extensions apply, measured from the original house. A householder application costs £548 (or £575 for applications made from 8 December 2026).
Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.
Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.
Design points for St Austell homes
Garage walls and the door opening
Garage walls are often a single skin of brick or block with piers, and the wide door opening needs a beam over it. Many over-garage extensions need new inner walls or a steel frame to carry the floor and to insulate properly, which we confirm before the design is fixed.
Matching the house
A room over a garage usually sits beside the front of the house in full view, so roof form, ridge height, windows and brick matter. Setting the front wall and ridge back slightly from the main house usually helps it look as if it belongs.
How we'd run your project
Free site visit
We visit your home in St Austell, look at the structure, access and boundaries, and talk through what you want the new rooms to do.
Drawings, then consent
We draw the scheme, check it against the rules in England, and take it through the right consent with the council.
Price it properly
Once the engineer's calculations are in, we fix the build price in writing, with a clear list of what's included.
Build and hand over
We manage the build from groundworks to decoration-ready finish and hand over with the completion paperwork.
Questions about extensions over a garage in St Austell
How much does an extension over a garage cost in St Austell?
Our guide for South West England, which covers St Austell, is £1,800–£2,630 per m² including VAT. A typical project with 3 m × 6 m of new first-floor space (18 m²) comes to about £32,500–£47,500. Design and approval fees are extra, and we fix the build price in writing once the design is agreed.
Do I need planning permission for an extension over a garage in St Austell?
St Austell is in England, so England planning rules apply. Planning permission is needed: in England, permitted development only allows single-storey extensions to the side. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.
How long does an extension over a garage take?
Allow 4 to 8 weeks for survey and design, then the approval period (councils should decide householder applications within 8 weeks of validation), then 4 to 8 weeks of technical design, which can overlap. The build itself usually takes 14 to 20 weeks, longer for large or complex designs.
Can I add an en-suite above the garage?
Yes, and it is a common choice for a main bedroom. The en-suite needs an extract fan under Part F, a route for the soil pipe down to the drains and enough fall for the waste, which can be harder over a garage. We plan the pipe route through the garage or an outside wall early.
How do I get into a room over the garage?
Usually through a new opening off the existing landing or a bedroom, so the stairs stay where they are. If the floor levels do not match, a step or two may be needed inside the new room. Where a landing opening is not practical, a new stair from a converted garage is an option.
Nearby
We also cover places near St Austell, including:
Other extensions in St Austell
- Rear
- Side
- Wraparound
- Part two-storey
- First floor
- Semi-detached
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in St Austell · Extensions over a garage across Cornwall
Tell us about your house in St Austell and we'll call you back to arrange a free, no-obligation visit.