Cornwall · Single-storey · Two-storey · Kitchen · Side return
House extensions across Cornwall.
Single-storey rear, two-storey side, kitchen extensions and side returns — designed, consented and (if you want) built by one Cornwall studio. Cornwall Council planning, Full Plans building regs and a tender-ready package that any Cornish builder can price without a list of provisional sums.
Extension types
What works on a Cornish house.
Single-storey rear extension
The Cornwall default — kitchen-diner, family room, garden link. Often within permitted development outside designations; needs planning inside Conservation Areas and AONB. Typically £55,000–£90,000 built for 20–30m².
Two-storey side / rear extension
Adds a bedroom and bathroom upstairs alongside the kitchen extension below. Always needs planning. Careful on ridge heights, eaves matching and materials — the case officer's first read.
Kitchen extension
Usually a single-storey rear with a glazed rear elevation, rooflights or lantern, and the kitchen designed in alongside the architecture rather than bolted on afterwards.
Side return / wrap-around
Closes off the unused alley on a Victorian terrace and combines with a rear extension to deliver a full-width back of house. Common across the older streets of Penzance, Falmouth, Redruth and Truro.
Glazed link / orangery
Joins a contemporary extension to an original cottage or barn without pretending to be old stone. Planners usually prefer it to a fake granite pastiche.
Cornwall specifics
Why extending in Cornwall isn't the same as extending in the home counties.
Coastal exposure
Most of the county sits in Wind Zone 3 or 4. Roof uplift, fixing schedules, render systems and window weather-tightness all need spec'ing for exposure — not copied from an inland detail.
Designation overlap
AONB, Conservation Area, World Heritage Site, Heritage Coast — most addresses touch at least one. We brief the constraints on day one so the design isn't redrawn at validation.
Granite, cob and slate
Pre-1900 Cornish fabric behaves nothing like modern blockwork. Junction details, breathability and lintel choices are project decisions, not Approved Document defaults.
Process
How a Cornwall extension runs.
Step 1
Free site visit
We come out, measure roughly, look at planning constraints and rough cost. No fee, no obligation.
Step 2
Feasibility & design
Sketch options, planning route, realistic cost range. Fixed fee, fixed scope.
Step 3
Planning submission
Drawings, statements and Cornwall Council submission. Householder applications decided in about 8 weeks.
Step 4
Building regs & structural
Full Plans at 1:50, junction details at 1:10, structural calcs coordinated. Submitted to Cornwall Building Control.
Step 5
Tender or build
Out to your builder for a fixed-price tender, or to our build team for a single-contract delivery.
Step 6
On site to handover
Site queries answered, Building Control inspections attended, completion certificate seen through.
FAQs
Cornwall extensions — what we get asked every week.
- Do I need planning permission for an extension in Cornwall?
- It depends on the size, the position and the designation status of your address. Many single-storey rear extensions sit comfortably inside permitted development. Two-storey extensions, side extensions wider than half the original, and almost anything inside a Conservation Area, AONB or on a listed building will need a full planning application to Cornwall Council. We check your address against the General Permitted Development Order on the first visit and tell you straight.
- How much does an extension cost in Cornwall?
- Budget £2,200–£2,800 per m² built for a standard single-storey rear extension in 2026 prices, more for kitchen-and-bathroom-heavy fit-outs or steel-heavy openings. A typical 25m² rear extension lands £55,000–£75,000 built. Coastal sites add 5–10% for upgraded weather-tightness and fixings. We quote a realistic range at feasibility, not a hopeful number to win the design fee.
- How long does an extension take in Cornwall, start to finish?
- Three to four months for design, planning and building regs running in parallel, then eight to sixteen weeks on site depending on size and finish. Cornwall Council householder planning is decided in about eight weeks from validation. Coastal and Conservation Area projects can add four to six weeks for additional consents.
- Can you extend a Cornish granite cottage without ruining the character?
- Yes — and most planners actively prefer a clearly contemporary extension that doesn't pretend to be original Cornish stone. A glazed or rendered link element joining a modern extension to the original cottage usually reads better than fake granite. We design for the property and the parish, not to a template.
- Do you handle both planning and building regulations?
- Yes — same studio, same project lead. Planning drawings, Cornwall Council submission, officer liaison, Full Plans building regs at 1:50, junction details at 1:10, structural engineering coordinated. One package, one fee schedule, no hand-offs.
- What about extensions inside the Cornwall AONB?
- Workable but design-led. Landscape impact, ridge height and material choice all carry extra weight. Single-storey rear extensions tucked behind the house are usually fine; two-storey or seaward-facing additions need a tighter design rationale and often a Landscape and Visual Impact note. We've worked across most of the AONB and know which moves the case officers will accept.
- Can you build the extension as well as design it?
- Yes. We run a full-build arm for clients who want one team and one point of accountability through the whole project. For clients who already have a Cornwall builder, we deliver a tender-ready Full Plans pack — no provisional sums, no 'builder to confirm' notes.
- Which Cornwall towns do you cover for extensions?
- All of them. Penzance, St Ives, Hayle, Helston, Falmouth, Truro, Newquay, St Austell, Redruth, Camborne, Wadebridge, Padstow, Bude, Liskeard, Saltash and every village in between. Free first visit anywhere in Cornwall — the studio is in Penzance.