Solar panels, heat pumps and insulation in Horsted Keynes conservation area
In the Horsted Keynes conservation area (Mid Sussex), 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 19 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. 107 homes inside the boundary have an energy certificate: 28.0% are solid-wall homes with no wall insulation, 1.9% heat with a gas boiler and 94.4% are rated D–G; 9 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
107homes with an energy certificate
28.0%solid walls, no insulation
1.9%heated by a gas boiler
9heat pumps
Article 4: Mid Sussex does not publish Article 4 areas on planning.data.gov.uk — check with the council.
What needs planning permission in Horsted Keynes
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: 19 in the area (grade I: 1, II*: 0). 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: 0% 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 = 107)
Walls
Homes
Share
Solid wall (brick or stone), no insulation
30
28.0%
Cavity wall, unfilled
27
25.2%
Cavity wall, insulated (as built or unspecified)
20
18.7%
Cavity wall, filled
14
13.1%
Timber frame
6
5.6%
Cavity wall, partly insulated
3
2.8%
Modern wall (U-value from the design)
3
2.8%
Solid wall, internal insulation
3
2.8%
Solid wall, external insulation
1
0.9%
Heating
Homes
Share
Oil
68
63.6%
LPG
14
13.1%
Electric (storage heaters, panels, boiler)
13
12.1%
Heat pump
9
8.4%
Gas boiler
2
1.9%
Solid fuel (wood, coal)
1
0.9%
Loft / roof insulation
Homes
Share
No insulation
9
8.4%
Under 200 mm
46
43.0%
200 mm or more
35
32.7%
Insulated (depth not recorded)
14
13.1%
Other
3
2.8%
Windows
Homes
Share
Double glazed
94
87.9%
Single glazed
9
8.4%
Secondary glazing
3
2.8%
Triple glazed
1
0.9%
DEF
Energy rating: C 6 (5.6%) · D 33 (30.8%) · E 52 (48.6%) · F 11 (10.3%) · G 5 (4.7%). Houses and bungalows: 100% of the homes; solar panels on 0.9% of the certificates. Most common build period on the certificates: before 1900. Designated: 1 January 1984.
Compared with Mid Sussex and England
Share of homes
Horsted Keynes
All 35 areas in Mid Sussex
England
Solid walls, no insulation
28.0%
25.2%
48.7%
Gas boiler
1.9%
77.3%
66.4%
Rated D–G
94.4%
—
56.5%
Caveats
Certificates describe a home when it was assessed; 38% of these are from 2020 or later (latest 12 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 Mid Sussex if in doubt.
Boundary: Mid Sussex District Council via planning.data.gov.uk (entity 44002111, reference 2855, 16.6 ha); the council's appraisal or map. Homes are placed by the coordinates of their UPRN (OS Open UPRN); addresses are not shown.