North Cornwall · TR5
House Extensions in Mithian Downs
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 Downs brief starts on the street, not the screen — Mithian Downs is a small rural hamlet in the TR5 area, with scattered homes, lanes and a deliberately quiet settlement pattern, with a building stock that leans toward small infill homes and farmhouses.
Mithian Downs sits in North Cornwall — covering TR5 from St Agnes, Mount Hawke, Trevellas outward.
- Cornwall AONB
- Rural / open-countryside policy area
- ✓ Measured-survey accuracy from day one
- ✓ One studio — design, planning and build under one roof
- ✓ Local to North Cornwall — not a national franchise
- ✓ Same team on paper as on site
Local watch-list
The TR5 constraints that shape a extension brief.
Watch #1
AONB landscape-impact scrutiny on visible elevations
Watch #2
Tighter Local Plan tests on isolated rural dwellings
Who this is for
Mithian Downs 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 Downs is its own job.
The main planning test is usually whether the proposal remains subordinate, locally detailed and acceptable on access, drainage and neighbour amenity. 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 Downs job runs as a TR5-specific piece of work — local policy, local fabric, local builders. Most of our extension work in Mithian Downs lands on small infill homes, 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 Downs.
01
Wind and sea-spray exposure can drive material choices on west-facing extensions; we detail accordingly.
02
Drainage on older Cornish properties is rarely on a clean modern map; CCTV survey before design is often money well spent.
03
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.
04
Cornish granite and slate-hung walls react differently to new openings than modern brickwork — lintel choice and structural sequencing matter.
Our process
How a Mithian Downs 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 Downs Extensions — local questions answered.
- How much does an extension cost in Mithian Downs?
- 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 Downs 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.
- 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.
- Will my house be liveable during the build?
- For most rear and side extensions, yes — we sequence the works so the kitchen and one bathroom stay functional until the new build is watertight and connected.
Mithian Downs is part of St Agnes
Mithian Downs sits inside the St Agnes catchment — we cover both as one extension territory.
See Extensions in St Agnes →Local proof — Most Mithian Downs 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 Mithian Downs
Nearby places we cover
For Mithian Downs homeowners weighing up a extension, the right starting point is honest feasibility — that's what we lead with, before any drawings.