Solar panels, heat pumps and insulation in Mill Road conservation area
In the Mill Road conservation area (Cambridge), 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. The area has 14 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. 3,883 homes inside the boundary have an energy certificate: 66.2% are solid-wall homes with no wall insulation, 78.2% heat with a gas boiler and 62.5% are rated D–G; 24 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
3,883homes with an energy certificate
66.2%solid walls, no insulation
78.2%heated by a gas boiler
24heat pumps
Article 4: Cambridge publishes its Article 4 areas on planning.data.gov.uk and none overlaps this area; a direction can still exist on paper, so check with the council.
What needs planning permission in Mill Road
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: 14 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: 28% 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 = 3,883)
Walls
Homes
Share
Solid wall (brick or stone), no insulation
2,572
66.2%
Cavity wall, insulated (as built or unspecified)
623
16.0%
Modern wall (U-value from the design)
358
9.2%
Solid wall, internal insulation
113
2.9%
Cavity wall, filled
50
1.3%
Timber frame
48
1.2%
Cavity wall, partly insulated
39
1.0%
Cavity wall, unfilled
39
1.0%
Other or not known
17
0.4%
Solid wall, insulated
10
0.3%
Solid wall, external insulation
9
0.2%
Solid wall, partly insulated
3
0.1%
Cavity wall, internal or external insulation
2
0.1%
Heating
Homes
Share
Gas boiler
3,035
78.2%
Electric (storage heaters, panels, boiler)
525
13.5%
Communal heating
291
7.5%
Heat pump
24
0.6%
LPG
5
0.1%
Solid fuel (wood, coal)
3
0.1%
Loft / roof insulation
Homes
Share
No insulation
620
16.0%
Under 200 mm
1,043
26.9%
200 mm or more
921
23.7%
Insulated (depth not recorded)
521
13.4%
Flat or other home above
560
14.4%
Other
218
5.6%
Windows
Homes
Share
Double glazed
3,440
88.6%
Single glazed
385
9.9%
Secondary glazing
50
1.3%
Triple glazed
8
0.2%
BCDE
Energy rating: A 3 (0.1%) · B 344 (8.9%) · C 1,108 (28.5%) · D 1,846 (47.5%) · E 502 (12.9%) · F 57 (1.5%) · G 23 (0.6%). Houses and bungalows: 72% of the homes; solar panels on 0.3% of the certificates. Most common build period on the certificates: before 1900. Designated: 21 November 2018.
Compared with Cambridge and England
Share of homes
Mill Road
All 18 areas in Cambridge
England
Solid walls, no insulation
66.2%
52.2%
48.7%
Gas boiler
78.2%
71.7%
66.4%
Rated D–G
62.5%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 59% of these are from 2020 or later (latest 31 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 Cambridge if in doubt.
Boundary: Cambridge City Council via planning.data.gov.uk (entity 44006866, reference 70, 99.6 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.