West Cornwall · TR13
Two-storey extension costs in Porthleven — what TR13 homeowners really pay
A two-storey extension in Porthleven sits at £2,000–£2,500/m² built for standard finishes, rising to £2,800/m² when the existing gable needs opening up. On fishermen's cottages above the harbour the biggest cost driver is almost never the shell — it's rooflines, matching stone or render, and how the new stair lands upstairs. 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. In Porthleven, that work is shaped by the place itself — Porthleven is the most southerly port on mainland Britain, AONB-designated, with a working harbour, dramatic winter swell and a terraced cliff-edge of Victorian cottages, with a building stock that leans toward fishermen's cottages above the harbour and converted lofts and warehouses.
Porthleven sits in West Cornwall — covering TR13 from Helston, Breage, Ashton outward.
- Conservation Area
- Cornwall AONB
- Coastal exposure zone
- ✓ Two-storey side: £90k–£150k build
- ✓ Two-storey rear: £110k–£180k build
- ✓ £2,000–£2,500/m² typical rate
- ✓ Full planning route mapped before design fee
Who this is for
Porthleven runs the full mix — owner-occupier, holiday-let, commercial and the occasional smallholding — so we scope every extension enquiry from the use-class up.
Local watch-list
Porthleven-specific issues we screen on the first visit.
Watch #1
Conservation Area material and fenestration controls in central Porthleven
Watch #2
AONB landscape-impact scrutiny on visible elevations
Watch #3
Coastal exposure driving fixing, render and joinery spec
Local proof — Most Porthleven extension clients we work with are second-time builders — they've seen the templated approach fail once already.
Get a free feasibility viewFAQs
Porthleven Extensions — local questions answered.
- Is a two-storey extension worth it in Porthleven?
- On average, yes — value uplift on TR13 stock typically covers the build cost within 3–5 years. The exception is where the existing bedroom layout won't take a new stair without losing a room.
- How much does a two-storey side extension cost in Porthleven?
- £90k–£150k for a 30–45m² double-storey side, including matching render/stone, new stair and one extra bedroom + en-suite upstairs.
- Does a two-storey extension need full planning in Porthleven?
- Yes — Conservation Area removes two-storey PD entirely. Full householder application, 8-week determination.
- 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. In Porthleven specifically, we'd start by checking the Conservation Area boundary before committing to a direction.
- 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 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.
Local context
Why Porthleven is its own job.
Locally, porthleven Conservation Area covers the harbour and most residential streets; AONB designation extends across the whole parish. Coastal exposure and views from the South West Coast Path are routine planning considerations. For extension specifically, parts of Porthleven sit within a designated Conservation Area, which means materials, fenestration and roof pitches all need to read sympathetically with the existing streetscape; the surrounding landscape falls inside the Cornwall Area of Outstanding Natural Beauty, so massing, height and landscape impact carry extra weight in any planning decision; coastal salt-laden air around Porthleven drives detailing choices — fixings, render systems and timber treatments all need to be specified for exposure. Which is why we scope Porthleven projects parish-up, not template-down — the TR13 context shapes the design from day one. Whether the project is on fishermen's cottages above the harbour in the centre or further out toward Praa Sands, the extension response is locally tuned.
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.
What we focus on
Extensions considerations specific to Porthleven.
01
Drainage on older Cornish properties is rarely on a clean modern map; CCTV survey before design is often money well spent.
02
Wind and sea-spray exposure can drive material choices on west-facing extensions; we detail accordingly.
03
Cornish granite and slate-hung walls react differently to new openings than modern brickwork — lintel choice and structural sequencing matter.
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.
Our process
How a Porthleven 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 fabric
Choosing a extension team that actually knows TR13.
Building stock
Across Porthleven (TR13) we work on fishermen's cottages above the harbour, Victorian terraces, modern coastal homes set back from the cliff, converted lofts and warehouses. Each stock type drives a different extension response — fishermen's cottages above the harbour in particular needs careful detailing here.
Parish & policy
Porthleven is its own town in West Cornwall, with planning history that's specific to the TR13 catchment.
Coverage
We cover TR13 from our studio, with regular extension jobs also running in Helston, Breage, Ashton. Most Porthleven site visits get booked within the same week.
What does a first Porthleven consultation cost?
Nothing. We come to the property, walk the site, talk through what works on a TR13 plot and follow up with a written feasibility note inside a week — no obligation either way.
Request a free visitOther services in Porthleven
Nearby places we cover
A well-scoped two-storey extension in Porthleven nearly always beats moving house. The value is in getting the upstairs plan right in the first sketch, not the last.
Get a two-storey feasibility for your Porthleven home
Free · No obligation
Book a free visit in Porthleven
No obligation. Reply usually same working day.