Extensions over a garage in Cornwall
Looking for extensions over a garage in Cornwall? We handle the full job: survey, design, approvals, structural design and build.
Cornwall at a glance
- Nation
- England
- Price region
- South West England
- Postcode areas
- PL, TR
- Towns covered
- 10 listed below, plus surrounding villages
- Approval route
- Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.
- Site visits
- Free, no obligation
What an extension over a garage involves
An extension over a garage suits you if you have an attached single garage beside the house and need an extra bedroom or a larger main bedroom with an en-suite. You get an inspection of the garage structure, a design that matches the house, the approvals your nation needs, structural design, building regulations approval and the build, carried out by vetted teams working under S&K.
Cornwall towns we list: Redruth (TR5), Falmouth (TR10), St Austell (PL23), Truro (TR1), Camborne (TR14) and Newquay (PL28). Every other address in Cornwall is covered as well.
Guide price in South West England
For budgeting in Cornwall, allow around £32,500–£47,500 for an extension over a garage with 3 m × 6 m of new first-floor space (18 m²). That's based on £1,800–£2,630 per m² including VAT for South West England. We'll give you a written design-stage price first, then a fixed build price once the drawings are agreed.
| Spec | Per m² | Typical project |
|---|---|---|
| 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 |
Rules in England
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.
The Party Wall etc. Act 1996 applies, so notices may be needed for work on or near a shared wall or boundary.
Getting the design right
Floor levels and headroom
Garage floors are often lower than the house, and the new first floor may not line up with the existing landing. We set the floor level to avoid awkward steps upstairs, while keeping enough headroom in the garage below for a car or storage.
Fire separation
If the garage stays a garage, the floor between it and the room above, and any door into the house, must give fire separation under building regulations. That usually means fire-resisting plasterboard ceilings, sealed gaps and a fire door, which we design in from the start.
How we work in Cornwall
Visit and first ideas
One of our team visits your house in Cornwall, checks the walls, roof and drains, and sketches out options with you.
Get it approved
Once you're happy with the design we submit it to the council for Cornwall and deal with any questions from the planning officer.
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
Foundations, walls, floor, roof, windows, then first and second fix. We break through into the house as late as we can.
Towns we cover in Cornwall
Extensions over a garage in Cornwall: questions
How much does an extension over a garage cost in Cornwall?
In South West England our guide is £1,800–£2,630 per m² including VAT, so about £32,500–£47,500 for 3 m × 6 m of new first-floor space (18 m²). Essential and Premium specs move that by roughly 8% down or 20% up.
Can my garage take a room on top?
Sometimes, but it needs checking. Many garages are built on shallow footings with thin walls, designed only for a single storey. We dig a trial hole and inspect the walls, and the structural engineer decides whether to reuse them, strengthen them, underpin the footings or build new foundations inside the garage.
Do I need to convert the garage as well?
No. You can keep the garage for parking or storage and build only the room above, as long as the floor between them and any door into the house meet fire separation rules. Converting the garage at the same time is often good value, because the walls and foundations may be upgraded anyway.
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.
Will I need planning permission in Cornwall?
Cornwall is in England. Planning permission is needed: in England, permitted development only allows single-storey extensions to the side.
Neighbouring areas
- Extensions over a garage in Devon
- Extensions over a garage in Swansea and Neath Port Talbot
- Extensions over a garage in Dyfed
- Extensions over a garage in Cardiff and the Vale of Glamorgan
All extension services in Cornwall · About extensions over a garage
Ready to see what a second storey could do for your home?
Book a free site visit. We'll look at your house, talk through options and explain the approvals you'd need, then price the design stage in writing.