North Cornwall · TR5
House Extensions in Mithian
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. A Mithian brief starts on the street, not the screen — Mithian is a rural parish in the TR5 area, with farmsteads, lanes and scattered homes defining its built character, with a building stock that leans toward rural cottages and scattered modern homes.
Mithian sits in North Cornwall — covering TR5 from St Agnes, Mount Hawke, Trevellas outward.
- Cornwall AONB
- Rural / open-countryside policy area
- ✓ Same team on paper as on site
- ✓ Fixed-fee planning packages, no surprise invoices
- ✓ Measured-survey accuracy from day one
- ✓ One studio — design, planning and build under one roof
Local watch-list
Local snags worth knowing before drawing a Mithian extension.
Watch #1
AONB landscape-impact scrutiny on visible elevations
Watch #2
Tighter Local Plan tests on isolated rural dwellings
Who this is for
Mithian 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 Mithian is its own job.
Open-countryside policy, access lanes, drainage and agricultural building history all need to be addressed before drawings go too far. For extension specifically, 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; 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. So every Mithian job runs as a TR5-specific piece of work — local policy, local fabric, local builders. Most of our extension work in Mithian lands on rural cottages, 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.
What we focus on
Extensions considerations specific to Mithian.
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
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 Mithian 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
Mithian Extensions — local questions answered.
- How much does an extension cost in Mithian?
- 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 Mithian specifically, we'd start by checking AONB landscape sensitivity 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.
- How long does the whole process take?
- Allow roughly three months for design and approvals, then twelve to twenty weeks on site for a typical single-storey extension. Wraparounds and two-storey add-ons take longer, mostly through approval and groundworks.
Mithian is part of St Agnes
Mithian sits inside the St Agnes catchment — we cover both as one extension territory.
See Extensions in St Agnes →Local proof — Our North Cornwall workload means a Mithian extension project never has to wait for an out-of-county team to drive down.
Get a free feasibility viewOther services in Mithian
Nearby places we cover
For Mithian homeowners weighing up a extension, the right starting point is honest feasibility — that's what we lead with, before any drawings.