South Cornwall · TR11 · Cornwall Council Central
House extension costs in Falmouth — what TR11 homeowners actually pay
Most Falmouth cost questions land in the same bracket: a single-storey rear sits roughly £2,200–£2,800/m² built, a two-storey side runs £2,000–£2,500/m², and anything touching a coastal elevation tends to add 8–12% for materials and detailing. We quote on measured drawings, not guesses. 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 Falmouth starts with a measured walk-round — Falmouth is a deep-water harbour town built around one of the world's largest natural harbours, with a thriving art college, Maritime Museum and a Victorian and Edwardian seafront, with a building stock that leans toward post-war suburbs at Trescobeas and Georgian merchants' houses.
Falmouth sits in South Cornwall — just off the A39; with Truro the closest city; 3 miles from Mawnan Smith.
- Conservation Area
- Cornwall AONB
- Coastal exposure zone
- ✓ Typical Falmouth single-storey rear: £55k–£85k build cost
- ✓ Two-storey side extension: £85k–£140k build cost
- ✓ Wrap-around / L-shaped: £110k–£180k build cost
- ✓ Design + planning + building regs fee from £4,800 (fixed)
Local watch-list
Falmouth-specific issues we screen on the first visit.
Watch #1
Marine exposure detailing on the harbour edge
Watch #2
HMO licensing pressure from university lets
Watch #3
Conservation Area sash-window restrictions on Arwenack and the Moor
Watch #4
Steep terraced plots above Stratton Place
Who this is for
In Falmouth the extension brief is almost always a private homeowner improving a forever home — so we lead with feasibility and long-term value, not show-home rhetoric.
Local context
Why Falmouth is its own job.
In Falmouth the planning picture is specific: falmouth has multiple Conservation Areas — Town Centre, Greenbank, Penryn River and Pendennis — each with its own character appraisal. Article 4 directions remove some permitted development rights in the Town Centre and seafront zones; HMO licensing is a separate active policy area. For extension specifically, parts of Falmouth 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 Falmouth drives detailing choices — fixings, render systems and timber treatments all need to be specified for exposure. That local reading is what makes a Falmouth (TR11) project different from a generic Cornwall scheme — and is the whole reason we work this way. On post-war suburbs at Trescobeas in particular — the kind you'll also find toward Flushing — 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.
What we focus on
Extensions considerations specific to Falmouth.
01
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.
02
Cornish granite and slate-hung walls react differently to new openings than modern brickwork — lintel choice and structural sequencing matter.
03
Wind and sea-spray exposure can drive material choices on west-facing extensions; we detail accordingly.
04
Drainage on older Cornish properties is rarely on a clean modern map; CCTV survey before design is often money well spent.
Recent work nearby
Recent HMO-to-family conversion on Killigrew Road undid 1990s subdivisions and reopened the original spine.
See more recent South Cornwall work →Our process
How a Falmouth 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.
FAQs
Falmouth Extensions — local questions answered.
- What's the average cost of a single-storey extension in Falmouth?
- For a typical 20–30m² rear extension in Falmouth (TR11) we'd expect £55k–£85k including VAT, depending on glazing spec and whether the kitchen is being reworked. Coastal exposure here pushes weather-tightness specs up, which is real money.
- Do extension costs in Falmouth include planning and building regs?
- Our fixed-fee design package covers measured survey, planning drawings, building regs and a tendered cost plan. Build cost is separate and quoted from drawings — never guessed from a phone call.
- What pushes a Falmouth extension over budget?
- Three things: ground conditions you didn't survey for, a planning condition that drives a material change, and "while we're at it" scope creep. We screen all three at feasibility stage so the number you start with is the number you finish on.
- 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. In Falmouth specifically, we'd start by checking the Conservation Area boundary before committing to a direction.
- 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.
- 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.
Falmouth is the hub for these neighbourhoods
We run extensions across Falmouth and the surrounding TR11 neighbourhoods — same studio, same site team.
Local proof — Most Falmouth homeowners come to us after a extension quote elsewhere felt vague on planning — we lead with feasibility instead.
Get a free feasibility viewOther services in Falmouth
Nearby places we cover
If you're scoping an extension in Falmouth, the honest number depends on three things: ground conditions, finish level and how much of the existing fabric stays. We'll tell you which bracket you're in before you commit to a fee.