Lizard Peninsula · TR12
Small rear extensions in Mullion — under-3m designs that work hard
A Mullion rear extension under 3m doesn't need to feel small. The compact TR12 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. The way we approach extension in Mullion starts with a measured walk-round — Mullion is the largest village on the Lizard Peninsula, AONB-designated, with a fifteenth-century church, a working cove and the highest concentration of period housing on the peninsula, with a building stock that leans toward modern AONB-sensitive replacement dwellings and Edwardian guesthouses.
Mullion sits in Lizard Peninsula — covering TR12 from Mawgan, Ruan Minor, The Lizard 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
Local watch-list
Local snags worth knowing before drawing a Mullion extension.
Watch #1
Conservation Area material and fenestration controls in central Mullion
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
Who this is for
Mullion 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 context
Why Mullion is its own job.
In Mullion the planning picture is specific: mullion Conservation Area covers the village centre; the wider parish is entirely within the AONB and includes Heritage Coast designation. Cliff-edge and coastal margin sites face the strictest controls in West Cornwall. For extension specifically, parts of Mullion 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 Mullion 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 local reading is what makes a Mullion (TR12) project different from a generic Cornwall scheme — and is the whole reason we work this way. On modern AONB-sensitive replacement dwellings in particular — the kind you'll also find toward The Lizard — 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 Mullion.
01
Cornish granite and slate-hung walls react differently to new openings than modern brickwork — lintel choice and structural sequencing matter.
02
Wind and sea-spray exposure can drive material choices on west-facing extensions; we detail accordingly.
03
Drainage on older Cornish properties is rarely on a clean modern map; CCTV survey before design is often money well spent.
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 Mullion 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
Mullion Extensions — local questions answered.
- What's the smallest worthwhile rear extension in Mullion?
- 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 Mullion 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 Mullion?
- For 8–15m² in Mullion, allow £30k–£55k including a basic kitchen refit. Coastal detailing and salt-resistant ironmongery add 5–8%.
- How much does an extension cost in Mullion?
- 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 Mullion 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.
Mullion is the hub for these neighbourhoods
We run extensions across Mullion and the surrounding TR12 neighbourhoods — same studio, same site team.
- Cury
TR12
- Gunwalloe
TR12
- Predannack
TR12
Local proof — Most Mullion 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 Mullion
Nearby places we cover
Local neighbourhoods in Mullion
Small extensions in Mullion 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 Mullion extension that punches above its size
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