Solar panels, heat pumps and insulation in High Street and King Street conservation area
In the High Street and King Street conservation area (Watford), 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 15 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. 142 homes inside the boundary have an energy certificate: 40.1% are solid-wall homes with no wall insulation, 57.0% heat with a gas boiler and 37.3% 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
142homes with an energy certificate
40.1%solid walls, no insulation
57.0%heated by a gas boiler
24heat pumps
Article 4: Watford does not publish Article 4 areas on planning.data.gov.uk — check with the council.
What needs planning permission in High Street and King 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), unless an Article 4 direction removes it — check with the council
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), unless an Article 4 direction removes it — check with the council
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)
Prior approval of appearance from the council, unless an Article 4 direction removes it — check with the council
Replacement windows and doors of similar appearance
No permission needed (permitted development), unless an Article 4 direction removes it — check with the council
Part 1 Class A, A.3(a)
Listed buildings: 15 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: 71% 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 = 142)
Walls
Homes
Share
Solid wall (brick or stone), no insulation
57
40.1%
Other or not known
34
23.9%
Modern wall (U-value from the design)
31
21.8%
Cavity wall, insulated (as built or unspecified)
5
3.5%
Solid wall, insulated
4
2.8%
Cavity wall, filled
3
2.1%
Cavity wall, partly insulated
3
2.1%
Cavity wall, unfilled
2
1.4%
Timber frame
2
1.4%
Solid wall, external insulation
1
0.7%
Heating
Homes
Share
Gas boiler
81
57.0%
Communal heating
25
17.6%
Heat pump
24
16.9%
Electric (storage heaters, panels, boiler)
12
8.5%
Loft / roof insulation
Homes
Share
No insulation
16
11.3%
Under 200 mm
18
12.7%
200 mm or more
16
11.3%
Insulated (depth not recorded)
30
21.1%
Flat or other home above
39
27.5%
Other
23
16.2%
Windows
Homes
Share
Double glazed
135
95.1%
Single glazed
7
4.9%
BCDE
Energy rating: B 44 (31.0%) · C 45 (31.7%) · D 37 (26.1%) · E 15 (10.6%) · F 1 (0.7%). Houses and bungalows: 29% of the homes; solar panels on 0.0% of the certificates. Most common build period on the certificates: 1900-1929. Designated: 8 June 2006.
Compared with Watford and England
Share of homes
High Street and King Street
All 10 areas in Watford
England
Solid walls, no insulation
40.1%
56.5%
48.7%
Gas boiler
57.0%
76.7%
66.4%
Rated D–G
37.3%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 57% of these are from 2020 or later (latest 27 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 Watford if in doubt.
Boundary: Watford Borough Council via planning.data.gov.uk (entity 44001731, reference 1701, 3.7 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.