Solar panels, heat pumps and insulation in Harwell conservation area
In the Harwell conservation area (Vale of White Horse), 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. The area has 56 listed buildings; on a listed building solar panels and heat pumps are not permitted development at all and need planning permission and listed building consent. 139 homes inside the boundary have an energy certificate: 30.9% are solid-wall homes with no wall insulation, 77.0% heat with a gas boiler and 66.2% 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
139homes with an energy certificate
30.9%solid walls, no insulation
77.0%heated by a gas boiler
2heat pumps
Article 4: Vale of White Horse does not publish Article 4 areas on planning.data.gov.uk — check with the council.
What needs planning permission in Harwell
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: 56 in the area (grade I: 1, II*: 5). The table is for houses that are not listed: on a listed building, solar panels and air source heat pumps are not permitted development at all (they need planning permission), and any of these works needs listed building consent.
Flats: 24% 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 = 139)
Walls
Homes
Share
Cavity wall, filled
44
31.7%
Solid wall (brick or stone), no insulation
43
30.9%
Cavity wall, insulated (as built or unspecified)
12
8.6%
Cavity wall, unfilled
11
7.9%
Timber frame
11
7.9%
Cavity wall, partly insulated
8
5.8%
Modern wall (U-value from the design)
6
4.3%
Solid wall, insulated
2
1.4%
Solid wall, internal insulation
2
1.4%
Heating
Homes
Share
Gas boiler
107
77.0%
Electric (storage heaters, panels, boiler)
30
21.6%
Heat pump
2
1.4%
Loft / roof insulation
Homes
Share
No insulation
19
13.7%
Under 200 mm
29
20.9%
200 mm or more
43
30.9%
Insulated (depth not recorded)
27
19.4%
Flat or other home above
14
10.1%
Other
7
5.0%
Windows
Homes
Share
Double glazed
124
89.2%
Single glazed
10
7.2%
Secondary glazing
3
2.2%
Triple glazed
2
1.4%
CDE
Energy rating: A 1 (0.7%) · B 6 (4.3%) · C 40 (28.8%) · D 65 (46.8%) · E 24 (17.3%) · F 3 (2.2%). Houses and bungalows: 76% of the homes; solar panels on 3.6% of the certificates. Most common build period on the certificates: before 1900. Designated: 22 July 1970.
Compared with Vale of White Horse and England
Share of homes
Harwell
All 54 areas in Vale of White Horse
England
Solid walls, no insulation
30.9%
39.8%
48.7%
Gas boiler
77.0%
56.2%
66.4%
Rated D–G
66.2%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 58% of these are from 2020 or later (latest 3 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 Vale of White Horse if in doubt.
Boundary: Vale of White Horse District Council via planning.data.gov.uk (entity 44004469, reference HAW, 18.7 ha). Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.