Two-storey side extensions in Cornwall
From first sketch to completion certificate, we deliver two-storey side extensions for homeowners across Cornwall.
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 a two-storey side extension involves
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.
Towns in Cornwall include Redruth (TR5), Falmouth (TR10), St Austell (PL23), Truro (TR1), Camborne (TR14) and Newquay (PL28). If yours isn't listed, we still cover it.
Guide price in South West England
A guide price for Cornwall: around £88,500–£119,000 for a 3 m × 7 m footprint on two floors (42 m² of new floor space). That works out at £2,110–£2,830 per m² of new floor space, including VAT at 20%. Keep a contingency of around 10% for things nobody can see until the ground is opened up.
| Spec | Per m² | Typical project |
|---|---|---|
| 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 |
Rules in England
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.
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
Access and services
Side extensions often cover the only route to the back garden, a gas meter, soil pipes or a drain run. We plan bin and bike access, move meters and pipes where needed and check drains early, because these items affect both cost and layout.
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.
How we work in Cornwall
Start at your house
We come to your home in Cornwall, measure up, check the ground floor walls and roof structure, and note anything near the boundaries.
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.
Technical design
We prepare the building regulations drawings, structural calculations and specification so the build price can be fixed.
Build and hand over
We manage the build from groundworks to decoration-ready finish and hand over with the completion paperwork.
Towns we cover in Cornwall
Two-storey side extensions in Cornwall: questions
How much does a two-storey side extension cost in Cornwall?
In South West England our guide is £2,110–£2,830 per m² including VAT, so about £88,500–£119,000 for a 3 m × 7 m footprint on two floors (42 m² of new floor space). Essential and Premium specs move that by roughly 8% down or 20% up.
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.
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
- Two-storey side extensions in Devon
- Two-storey side extensions in Swansea and Neath Port Talbot
- Two-storey side extensions in Dyfed
- Two-storey side extensions in Cardiff and the Vale of Glamorgan
All extension services in Cornwall · About two-storey side extensions
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.