Documents for a heat pump on a block of flats
Class G covers blocks of flats as well as houses, but not a communal array. Here is where the right stops and what a planning submission needs instead.
Planning a heat pump for a block of flats starts with a correction. Class G of Part 14 of Schedule 2 to the General Permitted Development Order 2015 covers the installation of an air source heat pump on, or within the curtilage of, a dwellinghouse or a block of flats, so the right is not limited to houses. What is limited is the kind of installation it covers. A single modest unit serving one flat may well be permitted development. A communal array on the roof serving forty flats, with new plant screening and an upgraded electrical supply, almost never is.
Read the current text of Class G before anything else, because its conditions have been amended more than once in recent years and an older summary will mislead you.
Where the permitted development right actually stops
Class G grants the right subject to conditions and limitations, and the limitations are where most block installations fail. The themes are consistent even as the detail changes:
- Capacity and size of the unit. The Class sets limits, and a plant item sized for a whole building exceeds them.
- Compliance with the relevant microgeneration planning standard, which is a condition of the right rather than a recommendation.
- Siting restrictions relative to the building, the curtilage and the boundary.
- Restrictions on land described in Article 2(3) of the Order, which covers conservation areas, National Landscapes, National Parks, the Broads and World Heritage Sites. On that land the right is narrowed, typically excluding walls or roof slopes fronting a highway.
- Total exclusion for listed buildings and land within their curtilage, and for scheduled monuments.
- A requirement to remove the equipment when it is no longer needed for microgeneration.
Beyond the Order there is a plainer problem. The right attaches to equipment installed for the purpose of microgeneration at the premises. A centralised plant installation serving many dwellings, with a distribution system, buffer vessels and a plant enclosure, is a different animal and should be treated as needing express permission. Where any doubt exists, a certificate of proposed lawful use or development under section 192 of the Town and Country Planning Act 1990 is the only formal way to confirm that works are lawful.
Noise assessment and the relevant method
Two methods apply depending on scale, and using the wrong one wastes the fee.
For a single domestic unit relying on Class G, the microgeneration planning standard sets the test. It works from the manufacturer's declared sound power level, the distance and the acoustic environment, and compares the calculated sound pressure level at an assessment position, taken a short distance from a window or door of a habitable room of a neighbouring property, against a fixed limit expressed in A-weighted decibels. The calculation is a defined procedure with a published worksheet, and the output is a pass or a fail.
For a communal installation, that standard does not fit and the assessment follows BS 4142:2014+A1:2019 instead, comparing the rating level of the plant against the measured background sound level, with corrections for tonal and intermittent character. That means a background survey covering the night period, because heat pumps run through the night on a heating or hot water demand and the night background is the hardest case. A Noise Impact Assessment of this kind is a report councils usually expect from a suitably qualified author, and professional review is strongly advised.
Two practical points. Fan speed modulation means the worst case is not always full output, so ask for the acoustic data across the operating range. And defrost cycles produce a short, tonal event that residents notice far more than a steady hum.
Siting, enclosures and maintenance access
On a flat roof the usual arrangement is a plant deck set back from the parapet, with acoustic screening on the sides facing habitable windows and an air path that does not recirculate. Three constraints fight each other here: the acoustic screen wants to be solid and tall, the units want free airflow, and the elevation wants the plant invisible from the street.
Resolve it with a section drawing rather than a plan. Show the parapet height, the screen height, the unit height and the sightline from the nearest upper floor window opposite. That one drawing answers the design question and the amenity objection together.
Leave room for maintenance. Filters, fans and refrigerant circuits need access, and a plant deck reached only by a ladder through a hatch will not be maintained. Safe access, a handrail where required and space to lift a unit out are part of the scheme, not an afterthought.
Visual impact on the elevation and roofscape
For a block in a street of similar buildings, the roofscape reads as a whole. Officers look at whether the plant breaks the roofline, whether screening matches the existing parapet material, and whether the installation is visible in the views that matter.
Produce verified or annotated views from two or three positions at street level and from any taller neighbour. Where the block sits in a conservation area or in the setting of a listed building, a short Heritage Statement assessing the effect on significance is needed, and the honest answer is sometimes to move the plant to a rear roof slope or a basement area instead.
Where individual units are proposed on balconies or rear elevations, the cumulative picture is what matters. Forty separate units appearing one at a time over five years produces a worse elevation than a single designed array, and some authorities now ask for a building-wide strategy in response.
Electrical capacity and the works that follow
A communal heat pump installation often needs more electrical capacity than the block has. The distribution network operator's connection process runs separately from planning and takes its own time, and the answer sometimes includes a new substation or a transformer upgrade.
That has planning consequences. A substation needs a location, access for the network operator, and sometimes its own permission. A Utilities Assessment setting out the existing supply, the proposed load and the connection strategy is worth preparing early, because discovering the capacity problem after permission is granted is the common failure on retrofit schemes.
Where the scheme is part of a wider refurbishment or an extension taking it over a threshold, an Energy Statement may be required by the local plan, and in London the energy hierarchy and carbon reporting requirements apply. The thresholds work in much the same way as those discussed for the ten unit major threshold.
Listed buildings and conservation areas
Class G does not apply to a listed building or land within its curtilage. Works to a listed building affecting its character as a building of special interest need listed building consent whether or not they amount to development, and that includes running pipework through historic fabric and fixing a unit to a rear elevation.
In a conservation area the right is narrowed rather than removed, and an Article 4 direction may remove it altogether. Check the direction's schedule, not a summary. Where consent is needed, the argument that usually works is a rear or roof location invisible from the street, with careful routing of pipework and a commitment to reinstate on removal.
Conditions to expect
- A noise limit expressed at a defined assessment position, sometimes with a requirement for post-installation verification.
- Acoustic screening to be installed as approved and retained.
- Colour, finish and screening material specified.
- Removal of the equipment and making good when no longer needed.
- Restrictions on operating the units in a particular mode or at particular hours, which is unusual and worth resisting where heating demand requires continuous operation.
The documents to submit
For a communal installation on a block, expect to prepare a planning statement describing the existing heating system and the proposal, a noise impact assessment to BS 4142 with a night-time background survey, drawings including roof plan, sections and elevations with the screening shown, a structural statement on roof loading, a utilities or electrical capacity note, and a heritage statement where the building is listed or in a conservation area. For a single unit relying on Class G, the paperwork is the microgeneration noise calculation and a record that each condition of the Class is met.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. Enter the building postcode on PlanScope to see which reports the constraint check flags before you commission the acoustic work.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Does permitted development cover heat pumps on flats?
Class G of Part 14 of Schedule 2 to the General Permitted Development Order 2015 applies to installations on or within the curtilage of a dwellinghouse or a block of flats, so flats are not excluded as a category. The conditions and limitations are what matter, and they have been amended recently, so read the current text rather than an older summary.
Why does a communal heat pump usually need permission?
Because the right attaches to equipment for microgeneration at the premises, subject to capacity and size limits that a plant installation serving a whole building exceeds. A centralised system with distribution pipework, buffer vessels and an acoustic enclosure should be treated as needing express permission, and a lawful development certificate is the only formal way to confirm otherwise.
Which noise method applies?
For a single domestic unit relying on Class G, the microgeneration planning standard calculation applies, comparing a calculated sound pressure level at an assessment position near a neighbouring habitable room window against a fixed limit. For a communal installation, use BS 4142:2014+A1:2019 with a measured background survey covering the night period, since heat pumps run overnight.
Do I need the freeholder's consent as well?
Almost always. In a block of flats the external walls, roof and risers are usually retained by the freeholder, so a licence to alter is needed whatever the planning position. Planning permission grants nothing in private law, and a leaseholder who installs plant on retained structure without consent risks a breach of covenant claim.
What about electrical capacity?
A communal installation often exceeds the block's existing supply, and the distribution network operator's connection process runs on its own timetable. The answer sometimes includes a transformer upgrade or a new substation, which needs a location, access and possibly its own permission. Deal with capacity before the planning application rather than after permission is granted.
Can a heat pump be installed on a listed building?
Class G does not apply to a listed building or land within its curtilage, and works affecting the character of the building as one of special interest need listed building consent whether or not they are development. That includes pipework routed through historic fabric. A rear or concealed location with careful routing and a commitment to reinstate is the argument that usually succeeds.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.