Solar panels, heat pumps and insulation in Chiswick House conservation area
In the Chiswick House 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. The area has 22 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. 990 homes inside the boundary have an energy certificate: 50.6% are solid-wall homes with no wall insulation, 79.4% heat with a gas boiler and 52.1% are rated D–G; 25 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
990homes with an energy certificate
50.6%solid walls, no insulation
79.4%heated by a gas boiler
25heat 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. (Dwellinghouses (C3) to small HMOs (C4) - borough-wide Article 4 Direction)
What needs planning permission in Chiswick House
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: 22 in the area (grade I: 17, II*: 0). 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: 47% 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 = 990)
Walls
Homes
Share
Solid wall (brick or stone), no insulation
501
50.6%
Modern wall (U-value from the design)
204
20.6%
Cavity wall, insulated (as built or unspecified)
106
10.7%
Cavity wall, unfilled
70
7.1%
Cavity wall, filled
58
5.9%
Timber frame
16
1.6%
Other or not known
9
0.9%
Solid wall, internal insulation
7
0.7%
Cavity wall, partly insulated
6
0.6%
Solid wall, insulated
5
0.5%
Solid wall, partly insulated
4
0.4%
Solid wall, external insulation
3
0.3%
Cavity wall, internal or external insulation
1
0.1%
Heating
Homes
Share
Gas boiler
786
79.4%
Communal heating
159
16.1%
Heat pump
25
2.5%
Electric (storage heaters, panels, boiler)
20
2.0%
Loft / roof insulation
Homes
Share
No insulation
191
19.3%
Under 200 mm
165
16.7%
200 mm or more
83
8.4%
Insulated (depth not recorded)
161
16.3%
Flat or other home above
289
29.2%
Other
101
10.2%
Windows
Homes
Share
Double glazed
898
90.7%
Single glazed
65
6.6%
Secondary glazing
24
2.4%
Triple glazed
3
0.3%
BCDE
Energy rating: B 196 (19.8%) · C 278 (28.1%) · D 362 (36.6%) · E 136 (13.7%) · F 17 (1.7%) · G 1 (0.1%). Houses and bungalows: 53% of the homes; solar panels on 0.4% of the certificates. Most common build period on the certificates: 1900-1929. Designated: 18 July 1977.
Compared with Hounslow and England
Share of homes
Chiswick House
All 29 areas in Hounslow
England
Solid walls, no insulation
50.6%
49.9%
48.7%
Gas boiler
79.4%
77.4%
66.4%
Rated D–G
52.1%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 44% of these are from 2020 or later (latest 27 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 44015581, reference HSLCA09, 78.3 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.