Solar panels, heat pumps and insulation in Harpenden conservation area
In the Harpenden conservation area (St Albans), 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 St Albans covers part of this area (about 0% of it) 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 39 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. 2,395 homes inside the boundary have an energy certificate: 31.1% are solid-wall homes with no wall insulation, 87.5% heat with a gas boiler and 52.7% 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
2,395homes with an energy certificate
31.1%solid walls, no insulation
87.5%heated by a gas boiler
24heat pumps
Article 4: An Article 4 direction published by St Albans covers part of this area (about 0% of it) 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. (Childwickbury and Ayres End Lane)
What needs planning permission in Harpenden
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
Inside the Article 4 part of the area: planning permission needed; elsewhere: no permission needed (permitted development)
Part 1 Class A, A.3(a)
Listed buildings: 39 in the area (grade I: 0, II*: 4). 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: 42% 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 = 2,395)
Walls
Homes
Share
Solid wall (brick or stone), no insulation
745
31.1%
Cavity wall, insulated (as built or unspecified)
503
21.0%
Modern wall (U-value from the design)
325
13.6%
Cavity wall, filled
311
13.0%
Cavity wall, unfilled
282
11.8%
Cavity wall, partly insulated
99
4.1%
Timber frame
74
3.1%
Solid wall, internal insulation
22
0.9%
Solid wall, insulated
14
0.6%
Cavity wall, internal or external insulation
10
0.4%
Other or not known
8
0.3%
Solid wall, external insulation
2
0.1%
Heating
Homes
Share
Gas boiler
2,095
87.5%
Electric (storage heaters, panels, boiler)
201
8.4%
Communal heating
71
3.0%
Heat pump
24
1.0%
LPG
2
0.1%
Oil
1
0.0%
Solid fuel (wood, coal)
1
0.0%
Loft / roof insulation
Homes
Share
No insulation
271
11.3%
Under 200 mm
590
24.6%
200 mm or more
424
17.7%
Insulated (depth not recorded)
360
15.0%
Flat or other home above
501
20.9%
Other
249
10.4%
Windows
Homes
Share
Double glazed
2,180
91.0%
Single glazed
134
5.6%
Secondary glazing
59
2.5%
Triple glazed
22
0.9%
BCDE
Energy rating: A 6 (0.3%) · B 313 (13.1%) · C 813 (33.9%) · D 820 (34.2%) · E 386 (16.1%) · F 54 (2.3%) · G 3 (0.1%). Houses and bungalows: 58% of the homes; solar panels on 0.4% of the certificates. Most common build period on the certificates: 1900-1929. Designated: 24 March 1969.
Compared with St Albans and England
Share of homes
Harpenden
All 45 areas in St Albans
England
Solid walls, no insulation
31.1%
37.1%
48.7%
Gas boiler
87.5%
76.8%
66.4%
Rated D–G
52.7%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 49% 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 St Albans if in doubt.
Boundary: St Albans City and District Council via planning.data.gov.uk (entity 44000007, reference CA1, 325.1 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.