Solar panels, heat pumps and insulation in Letchworth conservation area
In the Letchworth conservation area (North Hertfordshire), 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 78 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. 2,585 homes inside the boundary have an energy certificate: 65.4% are solid-wall homes with no wall insulation, 86.0% heat with a gas boiler and 70.8% are rated D–G; 4 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
2,585homes with an energy certificate
65.4%solid walls, no insulation
86.0%heated by a gas boiler
4heat pumps
Article 4: North Hertfordshire does not publish Article 4 areas on planning.data.gov.uk — check with the council.
What needs planning permission in Letchworth
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: 78 in the area (grade I: 0, II*: 8). 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: 25% 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 = 2,585)
Walls
Homes
Share
Solid wall (brick or stone), no insulation
1,690
65.4%
Cavity wall, insulated (as built or unspecified)
253
9.8%
Modern wall (U-value from the design)
184
7.1%
Cavity wall, unfilled
178
6.9%
Other or not known
72
2.8%
Cavity wall, filled
70
2.7%
Timber frame
58
2.2%
Solid wall, internal insulation
32
1.2%
Solid wall, external insulation
19
0.7%
Cavity wall, partly insulated
8
0.3%
Solid wall, insulated
8
0.3%
Solid wall, partly insulated
8
0.3%
Cavity wall, internal or external insulation
5
0.2%
Heating
Homes
Share
Gas boiler
2,222
86.0%
Electric (storage heaters, panels, boiler)
276
10.7%
Communal heating
78
3.0%
Heat pump
4
0.2%
Solid fuel (wood, coal)
3
0.1%
LPG
1
0.0%
Oil
1
0.0%
Loft / roof insulation
Homes
Share
No insulation
355
13.7%
Under 200 mm
822
31.8%
200 mm or more
610
23.6%
Insulated (depth not recorded)
355
13.7%
Flat or other home above
334
12.9%
Other
109
4.2%
Windows
Homes
Share
Double glazed
2,362
91.4%
Single glazed
140
5.4%
Secondary glazing
79
3.1%
Other
2
0.1%
Triple glazed
2
0.1%
CDE
Energy rating: B 154 (6.0%) · C 602 (23.3%) · D 1,236 (47.8%) · E 509 (19.7%) · F 73 (2.8%) · G 11 (0.4%). Houses and bungalows: 75% of the homes; solar panels on 0.2% of the certificates. Most common build period on the certificates: 1900-1929. Designated: 17 December 1974.
Compared with North Hertfordshire and England
Share of homes
Letchworth
All 44 areas in North Hertfordshire
England
Solid walls, no insulation
65.4%
44.7%
48.7%
Gas boiler
86.0%
67.6%
66.4%
Rated D–G
70.8%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 55% 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 North Hertfordshire if in doubt.
Boundary: North Hertfordshire District Council via planning.data.gov.uk (entity 44005788, reference 4953, 293.1 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.