How much does an extension cost in Twelveheads?

Build costs in Cornwall typically run from around £2,200 to £3,200 per square metre for a good-quality single-storey extension, more for kitchen-grade fit-out or complex glazing. We give a realistic budget before drawings start, not after. In Twelveheads specifically, we'd start by checking the latest parish-level planning history before committing to a direction.

Can you handle the build as well as the design?

Yes — that's the whole point of the studio. One contract, one point of contact, no finger-pointing between architect and builder when something needs a decision on site.

What about the Party Wall Act?

If you share a wall with a neighbour or build close to a boundary, the Act applies. We flag it early, recommend a surveyor and keep the programme aligned with the notice period.

Will my house be liveable during the build?

For most rear and side extensions, yes — we sequence the works so the kitchen and one bathroom stay functional until the new build is watertight and connected.

How long does the whole process take?

Allow roughly three months for design and approvals, then twelve to twenty weeks on site for a typical single-storey extension. Wraparounds and two-storey add-ons take longer, mostly through approval and groundworks.

Mid Cornwall · TR4

Extensions for Twelveheads (TR4)

Extensions are the bread and butter of Cornish homes — adding the kitchen-diner the original layout never had, the bedroom for a growing family, or the light and views the back of the house should always have had. Working in Twelveheads means starting from the TR4 context — Twelveheads is a former mining settlement in the TR4 area, with granite terraces, chapel buildings and industrial landscape character still visible, with a building stock that leans toward miners cottages and chapel conversions.

Twelveheads sits in Mid Cornwall — covering TR4 from Truro, St Michael Penkivel, Calenick outward.

Cornish Mining World Heritage Site
Rural / open-countryside policy area

Book a free Twelveheads site visit Call the studio More on Extensions →

✓ Fixed-fee planning packages, no surprise invoices
✓ Measured-survey accuracy from day one
✓ One studio — design, planning and build under one roof
✓ Local to Mid Cornwall — not a national franchise

Cornish mining-landscape ridge with engine-house silhouette

coastal contemporary build above the dunes

Our process

How a Twelveheads extension project runs.

Step 1
Brief
We meet on site, talk through how you live now and what's missing from the current layout.
Step 2
Design
Two or three sketch directions with rough budgets, then refinement of the chosen route.
Step 3
Approvals
Planning or Cert of Lawfulness, then a full building regs package.
Step 4
Build
Either through your own builder with our drawings, or as a full build by our team.
Step 5
Handover
Snag, certify, hand over the keys to your new space.

Typical single-storey rear extensions run twelve to twenty weeks on site; two-storey and wraparound projects sixteen to thirty weeks.

Local proof — Our Mid Cornwall workload means a Twelveheads extension project never has to wait for an out-of-county team to drive down.

Get a free feasibility view

What we focus on

Extensions considerations specific to Twelveheads.

01
Permitted development for rear extensions runs to four metres on a detached house, three on a semi or terrace — but Article 4 areas remove this in some parishes.
02
Extensions over a certain proportion of the original house trigger full Part L upgrade obligations to the existing building — worth knowing before brief is set.
03
Cornish granite and slate-hung walls react differently to new openings than modern brickwork — lintel choice and structural sequencing matter.
04
Wind and sea-spray exposure can drive material choices on west-facing extensions; we detail accordingly.

Local context

Why Twelveheads is its own job.

In Twelveheads the planning picture is specific: mining heritage, old plot widths and traditional materials make proportion and detailing more important than generic extension templates. For extension specifically, the wider area forms part of the Cornish Mining World Heritage Site, which adds a heritage assessment layer to most material changes; Cornwall Council's Local Plan applies tighter tests to isolated rural dwellings here, so design rationale and policy fit need to be set out clearly from the outset. That local reading is what makes a Twelveheads (TR4) project different from a generic Cornwall scheme — and is the whole reason we work this way. On miners cottages in particular — the kind you'll also find toward Malpas — the extension brief always has to read the existing fabric first.

Planning note

Most extensions in Cornwall are either permitted development or a straightforward householder application — but Conservation Area and AONB sites need a more careful design conversation upfront.

Local watch-list

The TR4 constraints that shape a extension brief.

Watch #1
World Heritage Site assessment on changes visible in the mining landscape
Watch #2
Tighter Local Plan tests on isolated rural dwellings

Twelveheads is part of Truro

Twelveheads sits inside the Truro catchment — we cover both as one extension territory.

See Extensions in Truro →

Local fabric

Twelveheads extensions — the local-studio difference.

Building stock

Across Twelveheads (TR4) we work on miners cottages, granite terraces, chapel conversions, workers cottages, post-war estates. Each stock type drives a different extension response — miners cottages in particular needs careful detailing here.

Parish & policy

Twelveheads sits in the parish of Twelveheads, which matters for how parish-level consultation lands on a extension application.

Coverage

We cover TR4 from our studio, with regular extension jobs also running in Truro, St Michael Penkivel, Calenick. Most Twelveheads site visits get booked within the same week.

Can you handle both planning and build in Twelveheads?

Yes — design, planning, building regs and full construction run under one roof. For clients with an existing Twelveheads builder we can stop at a tender-ready Full Plans pack instead.

Request a free visit

Who this is for

Twelveheads runs the full mix — owner-occupier, holiday-let, commercial and the occasional smallholding — so we scope every extension enquiry from the use-class up.

FAQs

Twelveheads Extensions — local questions answered.

How much does an extension cost in Twelveheads?: Build costs in Cornwall typically run from around £2,200 to £3,200 per square metre for a good-quality single-storey extension, more for kitchen-grade fit-out or complex glazing. We give a realistic budget before drawings start, not after. In Twelveheads specifically, we'd start by checking the latest parish-level planning history before committing to a direction.
Can you handle the build as well as the design?: Yes — that's the whole point of the studio. One contract, one point of contact, no finger-pointing between architect and builder when something needs a decision on site.
What about the Party Wall Act?: If you share a wall with a neighbour or build close to a boundary, the Act applies. We flag it early, recommend a surveyor and keep the programme aligned with the notice period.
Will my house be liveable during the build?: For most rear and side extensions, yes — we sequence the works so the kitchen and one bathroom stay functional until the new build is watertight and connected.
How long does the whole process take?: Allow roughly three months for design and approvals, then twelve to twenty weeks on site for a typical single-storey extension. Wraparounds and two-storey add-ons take longer, mostly through approval and groundworks.

Other services in Twelveheads

Nearby places we cover

If you're balancing ambition against TR4 planning realism, our Twelveheads extension work threads that needle without the usual drama.

Ready to discuss your project in Twelveheads?

Start a conversation

Extensions for Twelveheads (TR4)

How a Twelveheads extension project runs.

Brief

Design

Approvals

Build

Handover