North Cornwall · TR5
Small rear extensions in St Agnes — under-3m designs that work hard
A St Agnes rear extension under 3m doesn't need to feel small. The compact TR5 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. Reading St Agnes on the ground is half of the extension job — St Agnes is a former mining village on the north coast with a strong artistic community, AONB and World Heritage designation, and dramatic coastal mining ruins (Wheal Coates) on its doorstep, with a building stock that leans toward modern coastal architect builds and miners' terraces.
St Agnes sits in North Cornwall — covering TR5 from Mount Hawke, Mithian, Porthtowan outward.
- Conservation Area
- Cornwall AONB
- Cornish Mining World Heritage Site
- Coastal exposure zone
- ✓ 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
Our process
How a St Agnes 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 — We typically have one or two extension jobs live in the TR5 area at any time, so the local planning officers know our drawings on sight.
Get a free feasibility viewWhat we focus on
Extensions considerations specific to St Agnes.
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
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
Drainage on older Cornish properties is rarely on a clean modern map; CCTV survey before design is often money well spent.
Local context
Why St Agnes is its own job.
Around St Agnes (TR5), conservation Area covers Vicarage Road, Town Hill and the church area. AONB, Heritage Coast and World Heritage Site designations across the parish. Mining heritage shapes most planning conversations. For extension specifically, parts of St Agnes 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; the wider area forms part of the Cornish Mining World Heritage Site, which adds a heritage assessment layer to most material changes; coastal salt-laden air around St Agnes drives detailing choices — fixings, render systems and timber treatments all need to be specified for exposure. Reading St Agnes properly up front saves more time than any drawing tool ever will. Most of our extension work in St Agnes lands on modern coastal architect builds, with detailing that has to nod to the wider Mount Hawke streetscape.
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
St Agnes-specific issues we screen on the first visit.
Watch #1
Conservation Area material and fenestration controls in central St Agnes
Watch #2
AONB landscape-impact scrutiny on visible elevations
Watch #3
World Heritage Site assessment on changes visible in the mining landscape
Watch #4
Coastal exposure driving fixing, render and joinery spec
St Agnes is the hub for these neighbourhoods
We run extensions across St Agnes and the surrounding TR5 neighbourhoods — same studio, same site team.
- Porthtowan
TR4
- Mount Hawke
TR4
- Trevellas
TR5
- Mithian
TR5
- Goonbell
TR5
- Mithian Downs
TR5
Local fabric
St Agnes extensions — the local-studio difference.
Building stock
Across St Agnes (TR5) we work on miners' terraces, Victorian villas, Edwardian guesthouses, modern coastal architect builds, AONB-sensitive replacement dwellings. Each stock type drives a different extension response — modern coastal architect builds in particular needs careful detailing here.
Parish & policy
St Agnes is its own town in North Cornwall, with planning history that's specific to the TR5 catchment.
Coverage
We cover TR5 from our studio, with regular extension jobs also running in Mount Hawke, Mithian, Porthtowan. Most St Agnes site visits get booked within the same week.
Do you work in St Agnes regularly?
Yes — St Agnes and the wider TR5 catchment are core territory. We're typically on a North Cornwall site at least once a week, so logistics are baked in, not bolted on.
Request a free visitWho this is for
St Agnes 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
St Agnes Extensions — local questions answered.
- What's the smallest worthwhile rear extension in St Agnes?
- 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 Agnes 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 Agnes?
- For 8–15m² in St Agnes, allow £30k–£55k including a basic kitchen refit. Coastal detailing and salt-resistant ironmongery add 5–8%.
- How much does an extension cost in St Agnes?
- 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 St Agnes specifically, we'd start by checking the Conservation Area boundary 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.
Other services in St Agnes
Nearby places we cover
Local neighbourhoods in St Agnes
Small extensions in St Agnes succeed on detailing, not scale. A well-placed rooflight and the right floor finish often deliver more than an extra metre of footprint.
Sketch a small St Agnes extension that punches above its size
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