First-floor extensions in Truro

Useful details for planning a first-floor extension in Truro.

Postcode districts: TR1, TR2, TR3 and TR4
County / area: Cornwall, England
Price region: South West England
Guide price: £26,000–£37,500 (£1,850–£2,680 per m²)
Approval route: It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission.
Nearest towns: Falmouth (7.7 miles), Redruth (7.8 miles), Newquay (10.4 miles)
First visit: Free, no obligation

About a first-floor extension

A first-floor extension is a new upstairs room built on top of an existing single-storey part of your house, such as a rear kitchen extension, a utility or a side annexe. It adds a bedroom, bathroom or study without enlarging the footprint. Whether it works depends mainly on whether the walls and foundations below can carry the extra load.

We cover postcode districts TR1, TR2, TR3 and TR4 in and around Truro, along with neighbouring Falmouth, Redruth and Newquay.

What it costs in Truro

Expect a first-floor extension in Truro to land somewhere around £26,000–£37,500 for 4 m × 3.5 m of new first-floor space (14 m²). Our South West England guide rate is £1,850–£2,680 per m², including VAT. Design fees, structural calculations and approval fees are separate and listed on our prices page.

Spec	Per m²	4 m × 3.5 m of new first-floor space (14 m²)
Essential	£1,710–£2,460 per m²	£24,000–£34,500
Standard	£1,850–£2,680 per m²	£26,000–£37,500
Premium	£2,220–£3,210 per m²	£31,000–£45,000

Planning and building regulations in Truro

In England, adding a first floor turns a single-storey extension into one of more than one storey. To be permitted development, the extension as a whole must go no more than 3 m beyond the rear wall of the original house and stay at least 7 m from the rear boundary, with matching materials and roof pitch. Over a side extension it always needs planning permission, costing £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 Truro homes

Can the existing structure take it?

Many single-storey extensions were built with foundations, walls and lintels sized for one storey. We find out what is there with trial holes and, where available, the original building control drawings. The engineer then decides whether to reuse, strengthen or rebuild parts of the structure.

Matching the roofline

A first-floor extension often changes how the back or side of the house looks more than the original single storey did. Matching the main roof pitch and materials, and keeping the ridge below the main ridge, usually gives the best result and is expected for permitted development in England.

How we'd run your project

Understand the brief
At your home in Truro we agree what you need: bedroom count, bathroom, kitchen space, and how much garden you want to keep.
Drawings and permission
Our designers produce plans and elevations, then we take care of planning or permitted development checks with the council covering Truro.
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 first-floor extensions in Truro

How long does a first-floor 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.

How much does a first-floor extension cost in Truro?

Our guide for South West England, which covers Truro, is £1,850–£2,680 per m² including VAT. A typical project with 4 m × 3.5 m of new first-floor space (14 m²) comes to about £26,000–£37,500. 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 a first-floor extension in Truro?

Truro is in England, so England planning rules apply. It may be permitted development if it goes no more than 3 m beyond the original rear wall (counting any single-storey part) and stays 7 m from the rear boundary; otherwise it needs planning permission. If in doubt, a lawful development certificate or a planning application gives you certainty before you build.

What happens to the room below while the first floor is built?

The old roof is removed, so the room below is exposed for a short period. We fit temporary weather protection, plan the work so the roof comes off only when the new structure is ready, and agree with you which rooms will be out of use and for roughly how long.

Will the first-floor extension match my house?

It should, and in England matching materials and roof pitch is a condition of permitted development. We match brick, tile, mortar colour and window style where we can, and tell you at the design stage if an exact brick match is not available, so you can choose between the closest match and render or cladding.

Nearby

Nearby towns we cover for first-floor extensions:

Other extensions in Truro

All two-storey extension services in Truro · First-floor extensions across Cornwall

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