Two-storey side extensions in St Austell
Adding a two-storey side extension in St Austell gives you two new rooms stacked on one footprint. Here's how we'd approach it, what it typically costs and the rules that apply in England.
Quick reference for homeowners in St Austell.
- Postcode districts
- PL23, PL24, PL25 and PL26
- County / area
- Cornwall, England
- Price region
- South West England
- Guide price
- £88,500–£119,000 (£2,110–£2,830 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 a two-storey side extension
A two-storey side extension is a new two-floor addition built into the space beside your house, often over a driveway or side passage. It typically adds one or two bedrooms upstairs and a utility, study or larger kitchen below, without giving up rear garden.
We cover postcode districts PL23, PL24, PL25 and PL26 in and around St Austell, along with neighbouring Bodmin, Truro and Newquay.
What it costs in St Austell
Guide prices for two-storey side extensions in South West England are around £2,110–£2,830 per m² of new floor space, including VAT. For a typical project with a 3 m × 7 m footprint on two floors (42 m² of new floor space), that's roughly £88,500–£119,000. Kitchens, bathroom fittings and flooring are priced separately so you can compare like with like.
| Spec | Per m² | A 3 m × 7 m footprint on two floors (42 m² of new floor space) |
|---|---|---|
| Essential | £1,940–£2,610 per m² | £81,500–£109,500 |
| Standard | £2,110–£2,830 per m² | £88,500–£119,000 |
| Premium | £2,530–£3,400 per m² | £106,500–£143,000 |
Planning and building regulations in St Austell
In England, a two-storey side extension always needs householder planning permission, because permitted development only allows single-storey extensions beyond a side wall. The fee is £548 (or £575 for applications made from 8 December 2026), and councils should decide within 8 weeks of validation. Expect them to look at set-back, roof height, gaps to the boundary and the effect on neighbours.
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
Set-down and set-back
Councils usually want a two-storey side extension to look subordinate to the house. Setting the front wall back from the main front and dropping the ridge slightly below the main roof helps it read as an addition, and is often expected in local design guidance.
Side windows, boundaries and gutters
Upstairs windows in the side wall face the neighbour, so they are usually obscure-glazed and fixed, or left out. Building close to the boundary also raises questions about foundations, overhanging gutters and access for maintenance, so we design the eaves and gutter to stay within your land.
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 and permission
Our designers produce plans and elevations, then we take care of planning or permitted development checks with the council covering St Austell.
Structure and building control
A structural engineer sizes the foundations and steels, and we get building regulations approval before work starts.
Build it
The new structure goes up first, then we open into the house, finish inside and get the completion certificate.
Questions about two-storey side extensions in St Austell
How long does a two-storey side extension 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.
Which postcodes do you cover around St Austell?
We cover St Austell (PL23, PL24, PL25 and PL26) and nearby places including Bodmin, Truro and Newquay, plus the rest of Cornwall. The first site visit is free.
Do I need planning permission for a two-storey side extension 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.
Who handles building regulations for a project in St Austell?
We handle it as part of the project. What's needed in England: building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end. We prepare the drawings and the engineer's calculations, book the inspections and pass you the completion paperwork at the end.
Can I build a two-storey side extension over my driveway?
Yes, if the drive is wide enough for a useful room and the council accepts the design. You may lose off-road parking, which some councils weigh up, and the foundations need to suit the ground below. We check parking, drains and meter positions at the free site visit before any drawings are prepared.
Nearby
The same service in neighbouring towns:
Other extensions in St Austell
- Rear
- Wraparound
- Part two-storey
- Over a garage
- First floor
- Semi-detached
- Detached
- Kitchen and bedrooms
- Bedroom and en-suite
All two-storey extension services in St Austell · Two-storey side extensions across Cornwall
Want a figure first? Try our guide price tool, then book a free visit to firm it up.