Solar panels, heat pumps and insulation in Harrow on-the-Hill / South Hill Avenue conservation area
In the Harrow on-the-Hill / South Hill Avenue conservation area (Harrow), 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. 103 homes inside the boundary have an energy certificate: 37.9% are solid-wall homes with no wall insulation, 84.5% heat with a gas boiler and 60.2% are rated D–G; 2 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
103homes with an energy certificate
37.9%solid walls, no insulation
84.5%heated by a gas boiler
2heat pumps
Article 4: Harrow does not publish Article 4 areas on planning.data.gov.uk — check with the council.
What needs planning permission in Harrow on-the-Hill / South Hill Avenue
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: 59% 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 = 103)
Walls
Homes
Share
Solid wall (brick or stone), no insulation
39
37.9%
Cavity wall, unfilled
35
34.0%
Cavity wall, insulated (as built or unspecified)
13
12.6%
Cavity wall, partly insulated
10
9.7%
Solid wall, insulated
2
1.9%
Cavity wall, filled
1
1.0%
Modern wall (U-value from the design)
1
1.0%
Solid wall, external insulation
1
1.0%
Timber frame
1
1.0%
Heating
Homes
Share
Gas boiler
87
84.5%
Communal heating
13
12.6%
Heat pump
2
1.9%
Electric (storage heaters, panels, boiler)
1
1.0%
Loft / roof insulation
Homes
Share
No insulation
21
20.4%
Under 200 mm
18
17.5%
200 mm or more
6
5.8%
Insulated (depth not recorded)
16
15.5%
Flat or other home above
41
39.8%
Other
1
1.0%
Windows
Homes
Share
Double glazed
77
74.8%
Single glazed
22
21.4%
Secondary glazing
4
3.9%
CDE
Energy rating: B 4 (3.9%) · C 37 (35.9%) · D 43 (41.7%) · E 15 (14.6%) · F 4 (3.9%). Houses and bungalows: 41% of the homes; solar panels on 0.0% of the certificates. Most common build period on the certificates: 1930-1949.
Compared with Harrow and England
Share of homes
Harrow on-the-Hill / South Hill Avenue
All 31 areas in Harrow
England
Solid walls, no insulation
37.9%
55.6%
48.7%
Gas boiler
84.5%
90.9%
66.4%
Rated D–G
60.2%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 52% of these are from 2020 or later (latest 30 September 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 Harrow if in doubt.
Boundary: London Borough of Harrow via planning.data.gov.uk (entity 44009094, reference 174_HRW_CA6, 19.2 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.