Roseland · TR2
Small rear extensions in St Mawes — under-3m designs that work hard
A St Mawes rear extension under 3m doesn't need to feel small. The compact TR2 terraces and cottages we work on benefit most from a single tight move: a glazed corner, a side-light over the new kitchen, or a re-jigged level threshold to the garden. Under-3m and single-storey usually sits inside permitted development, which removes most of the planning risk. 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. What works on a TR2 plot rarely works elsewhere — St Mawes sits on the Roseland Peninsula opposite Falmouth across the Carrick Roads, with a Henrician castle, ferry harbour and one of the highest property value markets in Cornwall, with a building stock that leans toward Edwardian villas above the harbour and Victorian villas.
St Mawes sits in Roseland — covering TR2 from St Just in Roseland, Portscatho, Gerrans outward.
- Conservation Area
- Cornwall AONB
- Coastal exposure zone
- Rural / open-countryside policy area
- ✓ Under-3m PD route — no planning needed
- ✓ Glazed corner detailing maximises light gain
- ✓ Typical 8–15m² build: £30k–£55k
- ✓ On-site build: 10–14 weeks
Who this is for
St Mawes 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
Local snags worth knowing before drawing a St Mawes extension.
Watch #1
Conservation Area material and fenestration controls in central St Mawes
Watch #2
AONB landscape-impact scrutiny on visible elevations
Watch #3
Coastal exposure driving fixing, render and joinery spec
Watch #4
Tighter Local Plan tests on isolated rural dwellings
Local proof — Our Roseland workload means a St Mawes extension project never has to wait for an out-of-county team to drive down.
Get a free feasibility viewFAQs
St Mawes Extensions — local questions answered.
- What's the smallest worthwhile rear extension in St Mawes?
- Anything from 8m² is worth doing if it unlocks a kitchen layout. Below that, the cost per m² makes a glazed door upgrade more sensible.
- Can I do a small extension in St Mawes under permitted development?
- If the property has its PD rights intact, single-storey rear extensions up to 3m (terraced/semi) or 4m (detached) are permitted. Conservation Area sites lose this — full planning needed.
- How much does a small extension cost in St Mawes?
- For 8–15m² in St Mawes, allow £30k–£55k including a basic kitchen refit. Coastal detailing and salt-resistant ironmongery add 5–8%.
- Do I need planning permission for an extension?
- Often no — single-storey rear extensions, side extensions and modest two-storey additions can sit inside permitted development on a typical detached house. Conservation Areas, AONB and Article 4 zones remove some of those rights, so we always check the address first. In St Mawes 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 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.
Local context
Why St Mawes is its own job.
Cornwall Council's lens on St Mawes is consistent: conservation Area covers the seafront and harbour; AONB and Heritage Coast across the peninsula. Tight policy resistance to second-home expansion in some Roseland parishes. For extension specifically, parts of St Mawes 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 St Mawes drives detailing choices — fixings, render systems and timber treatments all need to be specified for exposure; 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's why we treat every St Mawes project as a TR2-area job first — not a generic Cornwall job with a postcode bolted on. The Edwardian villas above the harbour that dominate St Mawes (and continue out toward Portscatho) set the tone for any extension scheme here.
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 St Mawes.
01
Cornish granite and slate-hung walls react differently to new openings than modern brickwork — lintel choice and structural sequencing matter.
02
Drainage on older Cornish properties is rarely on a clean modern map; CCTV survey before design is often money well spent.
03
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.
04
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.
Our process
How a St Mawes 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
Why a Roseland studio is the right fit for St Mawes extension.
Building stock
Across St Mawes (TR2) we work on Georgian seafront houses, Victorian villas, Edwardian villas above the harbour, modern architect-designed coastal homes. Each stock type drives a different extension response — Edwardian villas above the harbour in particular needs careful detailing here.
Parish & policy
St Mawes is its own town in Roseland, with planning history that's specific to the TR2 catchment.
Coverage
We cover TR2 from our studio, with regular extension jobs also running in St Just in Roseland, Portscatho, Gerrans. Most St Mawes site visits get booked within the same week.
How quickly can you visit a St Mawes site?
Usually within the same week. St Mawes (TR2) is on our regular Roseland run, alongside St Just in Roseland, Portscatho, Gerrans. First visits are free and you'll get an honest feasibility view inside seven days.
Request a free visitSt Mawes is the hub for these neighbourhoods
We run extensions across St Mawes and the surrounding TR2 neighbourhoods — same studio, same site team.
Other services in St Mawes
Nearby places we cover
Local neighbourhoods in St Mawes
Small extensions in St Mawes succeed on detailing, not scale. A well-placed rooflight and the right floor finish often deliver more than an extra metre of footprint.