Lizard Peninsula · TR12 · Cornwall Council West
Extending a period terrace in Mullion — side-return, rear and infill
Mullion's late-Victorian and Edwardian terraces share a predictable trio of headaches: the side-return dogleg, a chimney breast nobody wants to keep, and party walls to two neighbours. On TR12 stock we detail the roof junction, the flank cavity and the party-wall notices before drawings go anywhere near planning. 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 — just off the A394; covering TR12 from Mawgan, Ruan Minor, The Lizard outward.
- Conservation Area
- Cornwall AONB
- Coastal exposure zone
- Rural / open-countryside policy area
- ✓Side-return infill: typical £48k–£75k on a Mullion 2-bed terrace
- ✓Full-width rear + side return: £75k–£120k
- ✓Party wall notices handled in-house
- ✓Chimney-breast removal + gallows detailing coordinated with SE
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Free Mullion feasibility call
Tell us about your extension. We reply within 1 working day — no obligation.
Page purpose
Drawings only, or drawings through to handover in Mullion?
Both routes are open on a TR12 project, and the honest answer depends on whether you already have a builder you trust. Plenty of Mullion clients take the drawings, tender them locally, then come back to us for the build if the numbers do not stack up.
- Route one: feasibility, planning and a tender-ready technical pack
- Route two: the same pack, then the build under one contract
- Either way the survey and feasibility work is identical, so the decision can wait
- Fees quoted per stage against the TR12 scope, not as one opaque figure
Scope
Scope options for Mullion clients
Not every project needs every stage. On a Mullion job we scope to what the site and the consent route actually require.
Heritage and design statements
Written justification where designation makes the design case as important as the drawing.
Structural coordination
Calculations coordinated with the drawings so building control sees one consistent story.
Full design and build
One contract from first sketch to handover, with the same team on paper and on site.
Construction and technical drawings
1:10 and 1:20 details for the parts of the job builders normally have to guess at.
Building regulation drawings
Full Plans sets with sections, construction notes and coordinated structural information.
Local watch-list
Local snags worth knowing before drawing a Mullion extension.
Watch #1
Conservation Area controls on materials, window proportions and roof form through central Mullion
Watch #2
AONB landscape-impact testing on anything read in long views across Lizard Peninsula
Watch #3
Exposure detailing on granite cottages around the church — fixings, render systems and joinery specified for salt-laden air
Watch #4
Local Plan tests on isolated dwellings, plus lane access for plant and deliveries around Mullion
Who this is for
Straight facts about working with us here
- Applications for Mullion are handled through Cornwall Council, with Truro the nearest planning office we deal with regularly.
- Designated-area work is routine here, so heritage and landscape statements are produced alongside the drawings rather than outsourced.
- Drawings, planning and building regulations are all produced in-house, so an extension enquiry does not get passed between firms.
Planning rules change and every site is different. For the final position on your address, check with Cornwall Council as the local planning authority or the Planning Portal.
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.
Quick check
Want a straight answer on whether your Mullion project is worth pursuing?
Send a few details — we'll come back within 1 working day with a plain-English view on planning risk, likely cost band and whether it's a project we'd take on.
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Get a free feasibility view
For projects in Mullion and the TR12 area.
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. Historic fabric changes the sequence: survey first, then design around what the building can take. Consent routes for listed buildings sit separately from ordinary planning, so treat any general guidance here as a starting point and check with Cornwall Council. Coastal sites tend to raise questions about roof form, glazing exposure and how a scheme reads from public viewpoints. Those are policy judgements rather than fixed rules, so the local planning authority or the Planning Portal should confirm the position for a given plot.
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.
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.
- Do I need a party wall agreement for a side-return in Mullion?
- Almost always yes — cutting into the flank wall or excavating within 3m of the neighbouring foundation triggers the Party Wall etc. Act 1996. We serve notices at RIBA Stage 3 so consent lands before tender.
- Can I remove the chimney breast during a Mullion rear extension?
- Yes, but the stack above needs propping (usually a gallows bracket or steel) and a structural engineer's calc. On listed or Conservation Area terraces the stack usually has to stay externally even if the breast goes.
- How do you stop the extension looking bolted-on to a period terrace?
- Match the eaves line, keep the ridge subservient, and either contrast honestly (zinc/glass) or match brick+lime mortar. The worst outcome is a half-hearted "matching" brick that ages differently.
- 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.
- We live in the house. Can an extension in Mullion be done while we stay put?
- Usually yes for single-storey and rear work, with a temporary kitchen or bathroom arrangement agreed before the start. Whole-house remodels and roof work in Mullion are often easier if you move out for a few weeks. We set that expectation at feasibility stage rather than halfway through.
- 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.
Keep reading
Where to go next from Mullion
We cover Mullion and the wider TR12 district directly. Extensions enquiries here are common enough that we know the constraints before the first visit.
Other services in Mullion
Nearby places we cover
A Mullion terrace extension lives or dies on three details: the party-wall route, the flashing at the original rear-slope junction, and how the new kitchen ceiling meets the retained chimney breast. Get those right at design stage and the build is calm.
Book a period-terrace feasibility visit in Mullion
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