First, can the plan change?
A Class G failure usually comes down to one of a few rules, and several have simple fixes. Before applying, it is worth asking the installer whether a different plan would fit:
- Road-facing in a conservation area. Moving the unit to the back yard, a rear wall or the side return, no nearer the road than the house, usually solves it.
- On a flat roof edge. Moving it at least 1 metre in from every outer edge.
- Too big. A unit, or unit and enclosure, within 1.5 cubic metres on a house or 0.6 cubic metres on a building of flats.
- Fails the sound calculation. A different spot, a quieter model or a solid barrier.
- A second unit on a terrace or semi. One larger unit instead of two smaller ones.
Some failures cannot be designed away: a listed building, a site with a wind turbine, or a scheduled monument. For those, the application route is the only one.
Applying to the council
Planning applications for homes in the city go to Liverpool City Council. The council publishes validation guidance, its local list, setting out the plans and documents it expects on top of the national requirements, and it reviews every submission against both. For a heat pump, the facts the decision turns on are the same ones Class G uses, so the documents are much the same as for a lawful development certificate:
- A location plan and a site plan showing the outdoor unit's exact position, the roads around the property and the nearest neighbouring windows.
- Elevations or photographs showing how the unit will look on the building.
- The unit's data sheet, with dimensions and sound power level.
- The installer's MCS 020 a) calculation for the proposed position.
- For a listed building, a heritage statement explaining the effect on the building and how the design limits it.
Listed buildings: two consents
The council's guidance says that, in addition to planning permission, listed building consent is needed to alter a listed building in a way that affects its character, and that this applies to internal as well as external works, and to separate buildings within the grounds. For a heat pump that can include the outdoor unit, pipe routes through walls, a cylinder cupboard and radiator changes. The city has 1,569 listed-building records; the listed buildings page explains how to check the status of a building.
While you wait
Do not start work, or pay a non-refundable deposit, until the decision is in. If the grant is part of the plan, remember that the installer applies for it and then has a fixed period to finish the job, so the planning decision should come first. If permission is refused, the decision notice gives the reasons; read them with the installer, because they usually point to a change that would make a new application acceptable.
If you are not sure whether an application is needed at all, a lawful development certificate is the way to ask the council formally.