West Cornwall · TR18 · Cornwall Council West
Granny annexes in Penzance — self-contained living, done well
A granny annexe in Penzance is either an attached extension with a separate entrance, a garden building with independent services, or a garage conversion. Cornwall Council treats all three under the "ancillary residential" test — meaning they must remain connected to the main dwelling's planning use. Get the planning wording right and the design opens up. 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 Penzance on the ground is half of the extension job — Penzance is the principal town of Penwith, with a working harbour, Georgian and Regency seafront and a dense conservation core around Chapel Street and Market Jew Street, with a building stock that leans toward Victorian terraces and 1930s seafront flats.
Penzance sits in West Cornwall — just off the A30; with Truro the closest city; covering TR18 from Newlyn, Marazion, Heamoor outward.
- Conservation Area
- Cornish Mining World Heritage Site
- Coastal exposure zone
- ✓Attached annexe: £75k–£110k built
- ✓Detached garden annexe: £95k–£140k
- ✓Ancillary use planning included
- ✓Self-contained services throughout
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Local watch-list
Common Penzance pitfalls we plan around.
Watch #1
Listed-building constraints on Chapel Street and the seafront
Watch #2
Salt-driven render failure on west-facing elevations
Watch #3
Slim Georgian floorplans that resist standard rear-extension layouts
Watch #4
Article 4 restrictions on shopfront and window changes in the core
Who this is for
In Penzance the extension brief is almost always a private homeowner improving a forever home — so we lead with feasibility and long-term value, not show-home rhetoric.
Scope
The parts of the job we can take on in Penzance
Clients in Penzance take different slices of this list, and that is deliberate.
Full design and build
One contract from first sketch to handover, with the same team on paper and on site.
Measured survey
An accurate record of what is actually there, which is where most avoidable cost is removed.
Commercial drawings
Change of use, fit-out and access documentation for Class E and mixed-use premises.
Structural coordination
Calculations coordinated with the drawings so building control sees one consistent story.
Construction and technical drawings
1:10 and 1:20 details for the parts of the job builders normally have to guess at.
Who this is for
What we can genuinely back up in Penzance
- Commercial and mixed-use work in Penzance tends to sit around Long Rock Industrial Estate.
- Applications for Penzance are handled through Cornwall Council, with Truro the nearest planning office we deal with regularly.
- Sites we know on the ground here include the area around Chapel Street and Market Jew Street.
- 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.
Keep reading
Other work we do around Penzance
We cover Penzance and the wider TR18 district directly. Extensions enquiries here are common enough that we know the constraints before the first visit.
Page purpose
Drawings only, or drawings through to handover in Penzance?
Both routes are open on a TR18 project, and the honest answer depends on whether you already have a builder you trust. Plenty of Penzance 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 TR18 scope, not as one opaque figure
Local context
Why Penzance is its own job.
Around Penzance (TR18), the Penzance Conservation Area covers most of the central streets and seafront; expect close design scrutiny on shopfronts, sash windows, render colours and roofing materials. Listed buildings are common, including grade II* properties along Chapel Street. For extension specifically, parts of Penzance sit within a designated Conservation Area, which means materials, fenestration and roof pitches all need to read sympathetically with the existing streetscape; 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 Penzance drives detailing choices — fixings, render systems and timber treatments all need to be specified for exposure. Reading Penzance properly up front saves more time than any drawing tool ever will. Most of our extension work in Penzance lands on Victorian terraces, with detailing that has to nod to the wider Gulval streetscape. Where a property sits inside a conservation area or is listed, the assessment tends to turn on materials, window detailing and how visible the change is from the street rather than floor area alone. Cornwall Council's conservation team, or the Planning Portal, is the right place to confirm what applies to a specific address. Salt air and prevailing wind change specification long before they change planning. We tend to draw weathering details in full, then check whether coastal or AONB policy narrows the design options for this address.
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 Penzance.
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.
Quick check
Want a straight answer on whether your Penzance 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 Penzance and the TR18 area.
Recent work nearby
Recent feasibility on a Regency seafront flat just off the Promenade — rear lightwell strategy in lieu of a side return.
See more recent West Cornwall work →Our process
How a Penzance 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
Penzance Extensions — local questions answered.
- Do I need planning permission for a granny annexe in Penzance?
- Yes — annexes always need planning consent to establish ancillary residential use. Attached annexes go through householder; detached garden annexes need full planning.
- How much does a granny annexe cost in Penzance?
- £75k–£140k for a 30–55m² annexe with kitchenette, bedroom, bathroom and living area. Detached garden annexes cost 10–20% more than attached (utility runs and separate roof).
- Can we let out the annexe as a holiday let later?
- Only with a further change-of-use application. Ancillary consent explicitly ties the annexe to the main dwelling — subletting breaches that condition.
- 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. In Penzance specifically, we'd start by checking the Conservation Area boundary before committing to a direction.
- How much does an extension cost in Cornwall?
- 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.
- 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.
Local proof — Recent extension enquiries from Penzance have clustered around Victorian terraces — we know the route through Cornwall Council on these.
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Nearby places we cover
A Penzance granny annexe is 50% design, 50% planning wording — get the ancillary-use case right and everything downstream is straightforward.
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