Solar panels, heat pumps and insulation in Mill Hill conservation area
In the Mill Hill conservation area (Barnet), 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 Barnet covers this area and removes permitted development rights for replacement windows and doors, and other alterations to the house, alterations to the roof (e.g. rooflights), painting the outside, so there these need planning permission too. The area has 46 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. 977 homes inside the boundary have an energy certificate: 16.9% are solid-wall homes with no wall insulation, 40.0% heat with a gas boiler and 24.6% are rated D–G; 7 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
977homes with an energy certificate
16.9%solid walls, no insulation
40.0%heated by a gas boiler
7heat pumps
Article 4: An Article 4 direction published by Barnet covers this area and removes permitted development rights for replacement windows and doors, and other alterations to the house, alterations to the roof (e.g. rooflights), painting the outside, so there these need planning permission too. (Article 4 Agricultural Land Restriction Area 2; Article 4 Agricultural Land Restriction Area 3; Article 4 Small Houses in Multiple Occupation (HMO) Area 1; Article 4 for Mill Hill CA Area 1; Article 4 for Mill Hill CA Area 2; Article 4 for Mill Hill CA Area 3)
What needs planning permission in Mill Hill
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: 46 in the area (grade I: 0, II*: 1). 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: 75% 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 = 977)
Walls
Homes
Share
Modern wall (U-value from the design)
656
67.1%
Solid wall (brick or stone), no insulation
165
16.9%
Cavity wall, insulated (as built or unspecified)
57
5.8%
Solid wall, insulated
36
3.7%
Cavity wall, unfilled
31
3.2%
Timber frame
8
0.8%
Cavity wall, filled
6
0.6%
Other or not known
6
0.6%
Cavity wall, partly insulated
5
0.5%
Solid wall, internal insulation
5
0.5%
Cavity wall, internal or external insulation
2
0.2%
Heating
Homes
Share
Communal heating
571
58.4%
Gas boiler
391
40.0%
Electric (storage heaters, panels, boiler)
8
0.8%
Heat pump
7
0.7%
Loft / roof insulation
Homes
Share
No insulation
35
3.6%
Under 200 mm
59
6.0%
200 mm or more
90
9.2%
Insulated (depth not recorded)
64
6.6%
Flat or other home above
476
48.7%
Other
253
25.9%
Windows
Homes
Share
Double glazed
921
94.3%
Single glazed
42
4.3%
Secondary glazing
12
1.2%
Other
1
0.1%
Triple glazed
1
0.1%
BCD
Energy rating: A 1 (0.1%) · B 625 (64.0%) · C 111 (11.4%) · D 186 (19.0%) · E 44 (4.5%) · F 8 (0.8%) · G 2 (0.2%). Houses and bungalows: 25% of the homes; solar panels on 0.3% of the certificates. Most common build period on the certificates: 2023. Designated: 20 December 1968.
Compared with Barnet and England
Share of homes
Mill Hill
All 16 areas in Barnet
England
Solid walls, no insulation
16.9%
48.2%
48.7%
Gas boiler
40.0%
84.8%
66.4%
Rated D–G
24.6%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 65% of these are from 2020 or later (latest 20 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 Barnet if in doubt.
Boundary: London Borough of Barnet via planning.data.gov.uk (entity 44002421, reference CA13, 186.6 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.