Permitted development, briefly
The General Permitted Development Order grants planning permission in advance for defined categories of work across England. Part 14 deals with renewable energy, and its Class G covers air source heat pumps on a house or a block of flats, while Class C covers ground source heat pumps. Work that keeps within every limit of its class needs no application to the borough council. Work that breaks one needs a normal application. The rules are national, so they are the same in all ten boroughs.
Class G after the 2025 changes
| Condition | House | Block of flats |
|---|---|---|
| Number of units | One; two on a detached house | One for the building |
| Size of each unit | Up to 1.5 cubic metres | Up to 0.6 cubic metres |
| Pitched roof | Not allowed | Not allowed |
| Flat roof | At least 1 metre from the edge | At least 1 metre from the edge |
| Wall facing a road | Not above the ground floor | Not above the ground floor |
| Conservation area | Nothing fronting a road or nearer the road | Nothing fronting a road or nearer the road |
| Listed building or scheduled monument | Not allowed | Not allowed |
| Sound | Must meet MCS 020 a) | Must meet MCS 020 a) |
Two more conditions apply to every unit: it must be sited, as far as practicable, to limit its effect on the building's appearance and the neighbours' amenity, and removed when no longer needed. It must not be used solely for cooling. SI 2025/560 also removed the old requirement to keep a unit a metre from the boundary, and dropped the wording that allowed an "equivalent" sound standard, so MCS 020 a) is the test.
What it means for Greater Manchester's homes
In 2021, 37.9% of households lived in semis and 28.5% in terraces, each allowed one unit; 14.2% in detached houses, allowed two; and 19.3% in flats, where the whole block shares one smaller unit. The block-of-flats limit matters most in Manchester, where 34.6% of households live in a flat. The road-facing rule matters most in the terraced towns, where the front wall meets the pavement and the back yard is the only practical spot.
The sound test
MCS 020 a) is a calculation done by the installer before fitting. It starts from the unit's published sound power and adjusts for the distance to the nearest habitable-room window of a neighbouring home, the hard surfaces near the unit and any solid barrier between the two. If the result is within the limit, the condition is met. In a terrace or a block, the neighbour's window is often close, so the position and the choice of model matter.
Ground source and Class C
Class C allows a ground source heat pump within the grounds of a house or a block of flats without Class G's size or position limits, because the collector is buried. In Greater Manchester few homes have the garden for horizontal trenches, but a borehole needs much less space. Check with the council if the property is listed or the ground holds anything protected.
Conservation areas and Article 4 directions
Each borough designates its own conservation areas, often including town centres. Class G still applies in them, but no unit may sit on a wall or roof that fronts a road or closer to the road than the building. A council can also withdraw permitted development rights in a defined area with an Article 4 direction. Check the borough's maps before choosing a position.
Listed buildings
Class G never applies to a listed building or within its curtilage. The ten boroughs hold 4,016 listed-building records, from 863 in Manchester and 554 in Oldham down to the low hundreds elsewhere. See listed buildings.
When to apply
- The building is listed, or might be.
- You want more units, or a bigger unit, than Class G allows, for example a shared system for a block.
- The only workable position is on a pitched roof, an upper road-facing wall or a road-facing wall in a conservation area.
- The sound calculation fails at every practical position.
- You want a lawful development certificate as proof the plan is permitted development.