Solar panels, heat pumps and insulation in Harley Street conservation area
In the Harley Street conservation area (Westminster), 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 Westminster covers this area and removes permitted development rights for replacement windows and doors, and other alterations to the house, so there these need planning permission too. The area has 234 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. 3,438 homes inside the boundary have an energy certificate: 66.9% are solid-wall homes with no wall insulation, 57.0% heat with a gas boiler and 39.6% are rated D–G; 143 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
3,438homes with an energy certificate
66.9%solid walls, no insulation
57.0%heated by a gas boiler
143heat pumps
Article 4: An Article 4 direction published by Westminster covers this area and removes permitted development rights for replacement windows and doors, and other alterations to the house, so there these need planning permission too. (Article 4 Basement Development Permitted Rights Removed; Article 4 Direction Class E To C3 In Central Activities Zone)
What needs planning permission in Harley Street
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
Planning permission needed (an Article 4 direction here removes this right)
Part 1 Class A, A.3(a)
Listed buildings: 234 in the area (grade I: 3, II*: 31). 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: 92% 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 = 3,438)
Walls
Homes
Share
Solid wall (brick or stone), no insulation
2,301
66.9%
Modern wall (U-value from the design)
323
9.4%
Timber frame
173
5.0%
Other or not known
148
4.3%
Solid wall, internal insulation
148
4.3%
Cavity wall, unfilled
133
3.9%
Solid wall, insulated
84
2.4%
Cavity wall, insulated (as built or unspecified)
56
1.6%
Cavity wall, partly insulated
50
1.5%
Solid wall, partly insulated
12
0.3%
Cavity wall, internal or external insulation
5
0.1%
Solid wall, external insulation
3
0.1%
Cavity wall, filled
2
0.1%
Heating
Homes
Share
Gas boiler
1,958
57.0%
Communal heating
870
25.3%
Electric (storage heaters, panels, boiler)
467
13.6%
Heat pump
143
4.2%
Loft / roof insulation
Homes
Share
No insulation
492
14.3%
Under 200 mm
93
2.7%
200 mm or more
50
1.5%
Insulated (depth not recorded)
286
8.3%
Flat or other home above
2,327
67.7%
Other
190
5.5%
Windows
Homes
Share
Double glazed
1,412
41.1%
Single glazed
1,268
36.9%
Secondary glazing
745
21.7%
Triple glazed
13
0.4%
BCDE
Energy rating: A 3 (0.1%) · B 287 (8.3%) · C 1,787 (52.0%) · D 945 (27.5%) · E 355 (10.3%) · F 43 (1.3%) · G 18 (0.5%). Houses and bungalows: 8% of the homes; solar panels on 0.0% of the certificates. Most common build period on the certificates: before 1900. Designated: 14 May 1990.
Compared with Westminster and England
Share of homes
Harley Street
All 56 areas in Westminster
England
Solid walls, no insulation
66.9%
66.4%
48.7%
Gas boiler
57.0%
59.2%
66.4%
Rated D–G
39.6%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 58% of these are from 2020 or later (latest 30 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 Westminster if in doubt.
Boundary: City of Westminster via planning.data.gov.uk (entity 44002856, reference 07/01600/CONARA, 53.0 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.