Solar panels, heat pumps and insulation in Rilla Mill conservation area
In the Rilla Mill conservation area (Cornwall), external wall insulation needs planning permission, and so does an air source heat pump on a wall or roof facing the road; one at the back or side, internal and loft insulation and solar panels on a roof slope normally do not. 56 homes inside the boundary have an energy certificate: 43% are solid-wall homes with no wall insulation, 4% heat with a gas boiler and 86% are rated D–G; 3 have a heat pump. EPC register November 2026; rules as at 21 October 2026.
Data: EPC register November 2026 (latest certificate per home), conservation area boundaries 3 November 2026, permitted development rules as at 21 October 2026 · calculated 5 November 2026 · Methodology and sources
56homes with an energy certificate
43%solid walls, no insulation
4%heated by a gas boiler
3heat pumps
Article 4: Cornwall does not publish Article 4 areas on planning.data.gov.uk — check with the council.
What needs planning permission in Rilla Mill
Work (house, not listed)
In a conservation area
Rule
Air source heat pump on a wall or roof facing the road, or nearer the road than the house
Planning permission needed
Part 14 Class G, G.1(j)
Air source heat pump at the back or side (outdoor unit up to 1.5 m³, MCS Planning Standards, one per house — two on a detached house)
No permission needed (permitted development), unless an Article 4 direction removes it — check with the council
Part 14 Class G
Solar panels on a pitched roof (up to 0.2 m proud, not above the ridge)
No permission needed (permitted development), unless an Article 4 direction removes it — check with the council
Part 14 Class A, A.2(c)
Solar panels on a wall, balcony or roof enclosure facing the road
Planning permission needed
Part 14 Class A, A.2(e)
Solar panels on a flat roof (up to 0.6 m above the roof)
Prior approval of appearance from the council, unless an Article 4 direction removes it — check with the council
Replacement windows and doors of similar appearance
No permission needed (permitted development), unless an Article 4 direction removes it — check with the council
Part 1 Class A, A.3(a)
Listed buildings: none recorded inside the boundary; on a listed building, solar panels and heat pumps are not permitted development and need listed building consent.
Flats: 5% of the certified homes here are flats or maisonettes. Homes in a block of flats have no householder rights for alterations; heat pumps and solar have their own, tighter rules for blocks of flats.
The homes in the area (latest certificate per home, n = 56)
Walls
Homes
Share
Solid wall (brick or stone), no insulation
24
43%
Timber frame
9
16%
Cavity wall, insulated (as built or unspecified)
6
11%
Cavity wall, filled
3
5%
Modern wall (U-value from the design)
3
5%
Other or not known
3
5%
Solid wall, internal insulation
3
5%
Cavity wall, partly insulated
2
4%
Cavity wall, unfilled
2
4%
Solid wall, external insulation
1
2%
Heating
Homes
Share
Oil
27
48%
LPG
10
18%
Electric (storage heaters, panels, boiler)
9
16%
Heat pump
3
5%
Solid fuel (wood, coal)
3
5%
Communal heating
2
4%
Gas boiler
2
4%
Loft / roof insulation
Homes
Share
No insulation
6
11%
Under 200 mm
10
18%
200 mm or more
29
52%
Insulated (depth not recorded)
7
12%
Flat or other home above
1
2%
Other
3
5%
Windows
Homes
Share
Double glazed
53
95%
Single glazed
3
5%
CDEF
Energy rating: A 1 (2%) · B 1 (2%) · C 6 (11%) · D 14 (25%) · E 17 (30%) · F 13 (23%) · G 4 (7%). Houses and bungalows: 95% of the homes; solar panels on 2% of the certificates. Most common build period on the certificates: before 1900. Designated: 1 April 1988.
Compared with Cornwall and England
Share of homes
Rilla Mill
All 145 areas in Cornwall
England
Solid walls, no insulation
43%
56.0%
48.7%
Gas boiler
4%
51.3%
66.4%
Rated D–G
86%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 50% of these are from 2020 or later (latest 20 March 2026). “No insulation (assumed)” is the assessor's default for older walls.
The rules are England's national permitted development rules (General Permitted Development Order 2015, Schedule 2, as at 21 October 2026). They do not cover building regulations or a council's own conditions. This is not a planning decision: ask Cornwall if in doubt.
Boundary: Cornwall Council via planning.data.gov.uk (entity 44002644, reference DCO158, 25.8 ha). Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.