Solar panels, heat pumps and insulation in Thorney Hedge conservation area
In the Thorney Hedge conservation area (Hounslow), 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. An Article 4 direction published by Hounslow covers this area but deals with other things (such as changes of use); it does not change the rules below. 233 homes inside the boundary have an energy certificate: 78.5% are solid-wall homes with no wall insulation, 92.3% heat with a gas boiler and 59.2% are rated D–G; 5 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
233homes with an energy certificate
78.5%solid walls, no insulation
92.3%heated by a gas boiler
5heat pumps
Article 4: An Article 4 direction published by Hounslow covers this area but deals with other things (such as changes of use); it does not change the rules below. (Change of use or development that would result in new dwellings (Class MA/ZA); Dwellinghouses (C3) to small HMOs (C4) - borough-wide Article 4 Direction)
What needs planning permission in Thorney Hedge
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)
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)
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)
Replacement windows and doors of similar appearance
No permission needed (permitted development)
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: 65% 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 = 233)
Walls
Homes
Share
Solid wall (brick or stone), no insulation
183
78.5%
Modern wall (U-value from the design)
18
7.7%
Timber frame
11
4.7%
Solid wall, internal insulation
10
4.3%
Cavity wall, insulated (as built or unspecified)
7
3.0%
Solid wall, insulated
2
0.9%
Cavity wall, partly insulated
1
0.4%
Cavity wall, unfilled
1
0.4%
Heating
Homes
Share
Gas boiler
215
92.3%
Electric (storage heaters, panels, boiler)
12
5.2%
Heat pump
5
2.1%
Communal heating
1
0.4%
Loft / roof insulation
Homes
Share
No insulation
56
24.0%
Under 200 mm
35
15.0%
200 mm or more
17
7.3%
Insulated (depth not recorded)
30
12.9%
Flat or other home above
81
34.8%
Other
14
6.0%
Windows
Homes
Share
Double glazed
200
85.8%
Single glazed
33
14.2%
CDE
Energy rating: A 2 (0.9%) · B 13 (5.6%) · C 80 (34.3%) · D 89 (38.2%) · E 40 (17.2%) · F 6 (2.6%) · G 3 (1.3%). Houses and bungalows: 35% of the homes; solar panels on 0.0% of the certificates. Most common build period on the certificates: 1900-1929. Designated: 3 December 2002.
Compared with Hounslow and England
Share of homes
Thorney Hedge
All 29 areas in Hounslow
England
Solid walls, no insulation
78.5%
49.9%
48.7%
Gas boiler
92.3%
77.4%
66.4%
Rated D–G
59.2%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 58% of these are from 2020 or later (latest 9 October 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 Hounslow if in doubt.
Boundary: London Borough of Hounslow via planning.data.gov.uk (entity 44015603, reference HSLCA24, 5.0 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.