Solar panels, heat pumps and insulation in Botwell: Thorn EMI conservation area
In the Botwell: Thorn EMI conservation area (Hillingdon), 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 Hillingdon 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 1 listed building; on a listed building solar panels and heat pumps are not permitted development at all and need planning permission and listed building consent. 528 homes inside the boundary have an energy certificate: 5.1% are solid-wall homes with no wall insulation, 0.0% heat with a gas boiler and 1.7% 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
528homes with an energy certificate
5.1%solid walls, no insulation
0.0%heated by a gas boiler
0heat pumps
Article 4: An Article 4 direction published by Hillingdon 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. (Changes of use from commercial, business and service uses to dwellinghouses; Construction of new dwellinghouses in employment areas; Residential extensions)
What needs planning permission in Botwell: Thorn EMI
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: 1 in the area. 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: 100% 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 = 528)
Walls
Homes
Share
Modern wall (U-value from the design)
350
66.3%
Cavity wall, insulated (as built or unspecified)
81
15.3%
Other or not known
54
10.2%
Solid wall (brick or stone), no insulation
27
5.1%
Timber frame
8
1.5%
Solid wall, internal insulation
6
1.1%
Solid wall, insulated
2
0.4%
Heating
Homes
Share
Communal heating
492
93.2%
Electric (storage heaters, panels, boiler)
36
6.8%
Loft / roof insulation
Homes
Share
No insulation
9
1.7%
Under 200 mm
1
0.2%
200 mm or more
7
1.3%
Insulated (depth not recorded)
34
6.4%
Flat or other home above
395
74.8%
Other
82
15.5%
Windows
Homes
Share
Double glazed
528
100.0%
BC
Energy rating: B 412 (78.0%) · C 107 (20.3%) · D 5 (0.9%) · E 3 (0.6%) · F 1 (0.2%). Houses and bungalows: 0% of the homes; solar panels on 0.0% of the certificates. Most common build period on the certificates: 2020. Designated: 20 June 1988.
Compared with Hillingdon and England
Share of homes
Botwell: Thorn EMI
All 32 areas in Hillingdon
England
Solid walls, no insulation
5.1%
25.5%
48.7%
Gas boiler
0.0%
62.7%
66.4%
Rated D–G
1.7%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 71% of these are from 2020 or later (latest 16 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 Hillingdon if in doubt.
Boundary: London Borough of Hillingdon via planning.data.gov.uk (entity 44015539, reference CA-16, 6.0 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.