Mid Cornwall · TR3
One studio for extension in Threemilestone
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. The way we approach extension in Threemilestone starts with a measured walk-round — Threemilestone is the western residential and retail-park suburb of Truro, with the West Cornwall Hospital site nearby and significant new estate development on the Langarth Garden Village land, with a building stock that leans toward office and retail conversions and modern Persimmon, Bellway and Wainhomes estates.
Threemilestone sits in Mid Cornwall — covering TR3 from Truro, Shortlanesend, Playing Place outward.
- ✓ Local to Mid Cornwall — not a national franchise
- ✓ Same team on paper as on site
- ✓ Measured-survey accuracy from day one
- ✓ One studio — design, planning and build under one roof
Our process
How a Threemilestone 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 — Recent extension enquiries from Threemilestone have clustered around office and retail conversions — we know the route through Cornwall Council on these.
Get a free feasibility viewWhat we focus on
Extensions considerations specific to Threemilestone.
01
Cornish granite and slate-hung walls react differently to new openings than modern brickwork — lintel choice and structural sequencing matter.
02
Wind and sea-spray exposure can drive material choices on west-facing extensions; we detail accordingly.
03
Drainage on older Cornish properties is rarely on a clean modern map; CCTV survey before design is often money well spent.
04
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.
Local context
Why Threemilestone is its own job.
Two things shape a Threemilestone application: parish character and policy. On policy — outside Conservation Area and AONB. Langarth Garden Village (3,500+ homes) is reshaping the west of Truro with strict design code expectations on adjacent sites. For extension specifically, Threemilestone sits outside the headline designations, which usually gives a slightly more flexible starting point — but parish-level character still matters. Get that local reading right and the rest of the Threemilestone programme tends to run on time. On office and retail conversions in particular — the kind you'll also find toward Playing Place — 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
Local snags worth knowing before drawing a Threemilestone extension.
Watch #1
Parish-level character expectations that don't appear on any policy map
Threemilestone is part of Truro
Threemilestone sits inside the Truro catchment — we cover both as one extension territory.
See Extensions in Truro →Local fabric
Threemilestone extensions — the local-studio difference.
Building stock
Across Threemilestone (TR3) we work on 1970s and 1980s estates, modern Persimmon, Bellway and Wainhomes estates, self-build plots in the Garden Village, office and retail conversions. Each stock type drives a different extension response — office and retail conversions in particular needs careful detailing here.
Parish & policy
Threemilestone sits in the parish of Kenwyn, which matters for how parish-level consultation lands on a extension application.
Coverage
We cover TR3 from our studio, with regular extension jobs also running in Truro, Shortlanesend, Playing Place. Most Threemilestone site visits get booked within the same week.
Can you handle both planning and build in Threemilestone?
Yes — design, planning, building regs and full construction run under one roof. For clients with an existing Threemilestone builder we can stop at a tender-ready Full Plans pack instead.
Request a free visitWho this is for
Threemilestone 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
Threemilestone Extensions — local questions answered.
- 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. In Threemilestone specifically, we'd start by checking the latest parish-level planning history before committing to a direction.
- 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.
- How much does an extension cost in Cornwall?
- 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.
- 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 Threemilestone
Nearby places we cover
The TR3 stretch of Mid Cornwall has its own rhythm; our extension work respects it, and Cornwall Council usually responds in kind.