Solar panels, heat pumps and insulation in St Stephen's conservation area
In the St Stephen's 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. 172 homes inside the boundary have an energy certificate: 79.7% are solid-wall homes with no wall insulation, 89.0% heat with a gas boiler and 73.8% are rated D–G; 0 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
172homes with an energy certificate
79.7%solid walls, no insulation
89.0%heated by a gas boiler
0heat 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 St Stephen's
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: 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 = 172)
Walls
Homes
Share
Solid wall (brick or stone), no insulation
137
79.7%
Cavity wall, unfilled
13
7.6%
Cavity wall, insulated (as built or unspecified)
6
3.5%
Modern wall (U-value from the design)
5
2.9%
Cavity wall, filled
3
1.7%
Cavity wall, partly insulated
2
1.2%
Other or not known
2
1.2%
Solid wall, internal insulation
2
1.2%
Solid wall, external insulation
1
0.6%
Timber frame
1
0.6%
Heating
Homes
Share
Gas boiler
153
89.0%
Electric (storage heaters, panels, boiler)
14
8.1%
Communal heating
5
2.9%
Loft / roof insulation
Homes
Share
No insulation
42
24.4%
Under 200 mm
43
25.0%
200 mm or more
28
16.3%
Insulated (depth not recorded)
19
11.0%
Flat or other home above
35
20.3%
Other
5
2.9%
Windows
Homes
Share
Double glazed
164
95.3%
Single glazed
5
2.9%
Triple glazed
2
1.2%
Secondary glazing
1
0.6%
CDE
Energy rating: B 7 (4.1%) · C 38 (22.1%) · D 85 (49.4%) · E 38 (22.1%) · F 3 (1.7%) · G 1 (0.6%). Houses and bungalows: 53% of the homes; solar panels on 1.7% of the certificates. Most common build period on the certificates: 1900-1929. Designated: 26 March 1987.
Compared with Hounslow and England
Share of homes
St Stephen's
All 29 areas in Hounslow
England
Solid walls, no insulation
79.7%
49.9%
48.7%
Gas boiler
89.0%
77.4%
66.4%
Rated D–G
73.8%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 62% of these are from 2020 or later (latest 18 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 44015599, reference HSLCA11, 10.1 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.