An air conditioning unit and a neighbour complaint

An air conditioning unit complaint from a neighbour almost always arrives after the unit is installed, and it raises two separate questions that get muddled. Did the installation need planning permission, and is the noise it makes unlawful. The answers are independent. A unit can be perfectly lawful in planning terms and still be abated as a statutory nuisance, and it can need permission while making almost no noise at all.

This walkthrough is illustrative. It follows a composite householder case built from the pattern these disputes usually take, not a real decision, and no figures are quoted from one.

The installation and how the complaint arose

A 1930s semi in a conservation area. The owner converted the loft into a home office, found it unbearable in summer, and had a wall mounted split system fitted with the condenser on the rear flank wall at first floor level, roughly half a metre from the boundary with the attached neighbour.

The condenser ran through the working day and, because the owner left it on a timer, through much of the night in July. The neighbour's bedroom window was about three metres away and at the same level.

The complaint went to environmental health first, which is usually what happens. Environmental health notified planning, and the planning enforcement team opened a case.

Whether permission was needed in the first place

The owner's installer had said no permission was needed, citing the permitted development rights for heat pumps. That advice was wrong, and it is the single most common error in this type of case.

Part 14 of Schedule 2 to the General Permitted Development Order 2015 grants rights for microgeneration equipment, and Class G of that Part deals with air source heat pumps, subject to conditions including compliance with the relevant microgeneration planning standards. A comfort cooling condenser is not an air source heat pump, so Class G did not apply.

That left Part 1, which grants rights for the enlargement, improvement or other alteration of a dwellinghouse. Two limitations mattered here. Part 1 rights apply to dwellinghouses and not to flats or maisonettes at all. And in a conservation area the rights are restricted, including for alterations to a wall facing a highway and for cladding, which narrows what can be done without an application.

The officer's conclusion was that permission was required. Where the position is arguable, the formal way to settle it is a certificate of lawfulness under section 191 or 192 of the Town and Country Planning Act 1990, not an installer's assurance.

The acoustic measurement taken by the officer

The environmental health officer measured at the neighbour's bedroom window over two nights, taking the background sound level with the unit switched off and the specific sound level with it running.

The approach followed the principles of BS 4142:2014+A1:2019, which is written for sound of an industrial and commercial nature and is routinely applied to building plant by environmental health teams, with a character correction applied for the tonal hum of the compressor. The measured specific level sat several decibels above the night-time background once the correction was applied, which under that method indicates an adverse impact.

The officer also noted the internal level with the window open, against the guideline night-time value for bedrooms in BS 8233:2014, and the distinct audibility of the compressor cycling on and off. Intermittency is what makes plant noise so complained about. A steady level is tolerated. A unit that starts up every twenty minutes is not.

For reference, the microgeneration planning standards that apply to heat pumps use a calculated sound level of 42 dB at the assessment position as the threshold for permitted development. The unit here was never within that figure, although as a cooling unit it was not subject to the standard in any event.

Relocating against replacing the unit

Three options were modelled before anything was bought.

1. Replace the unit with a quieter inverter model. The published sound power data showed a worthwhile improvement, but not enough on its own to bring the rating level down to the background.
2. Relocate the condenser to ground level at the far end of the rear garden, inside an acoustic enclosure, with longer refrigerant lines.
3. Keep the unit in place and add anti-vibration mounts and a barrier screen.

Option three was the cheapest and the weakest. A barrier only works if it breaks the line of sight between the source and the receiver, and at three metres with the receiver at the same height, a screen tall enough to do that would have been a planning problem in its own right.

Option two worked, because distance plus an enclosure plus removing the direct path to a first floor window attacks the problem on three fronts at once. The refrigerant pipe run cost more and the performance penalty was slight.

A Noise Impact Assessment was commissioned to model the relocated position before committing to it. On a domestic job that feels disproportionate until you consider the alternative, which is installing twice.

The retrospective application and its evidence

Development already carried out can be regularised by an application under section 73A of the 1990 Act. The application here covered the relocated unit rather than the installed one, which is the right way round: apply for what you intend to end up with.

The submission comprised existing and proposed elevations and a site plan showing the enclosure, the manufacturer's sound power data, the acoustic assessment with the predicted rating level at the neighbour's window, a short Heritage Statement addressing the effect on the conservation area, and a Planning Statement explaining the need and the mitigation.

The heritage element surprised the owner. A condenser in a rear garden within a conservation area still has to be assessed for its effect on the character and appearance of the area, and the answer is usually that a screened unit at low level in a garden is acceptable where a first floor flank wall unit visible from a side passage is not.

Conditions on operating hours

Permission was granted with four conditions: the acoustic enclosure to be installed before the unit is used and retained thereafter, a numerical noise limit expressed as a rating level relative to the measured background at a defined assessment position, no operation between 23:00 and 07:00, and the unit to be maintained in accordance with the manufacturer's schedule.

The hours condition is the one that resolved the dispute, and it was also the one the owner resisted hardest. Comfort cooling for a loft office does not need to run overnight. For a reader in the same position, offering an hours restriction voluntarily in the application is a strong move, because it removes the neighbour's principal objection and gives the officer a reason to recommend approval.

Note that a planning condition does not displace the statutory nuisance regime. Environmental health can still act under Part III of the Environmental Protection Act 1990 if the noise amounts to a statutory nuisance, even where the unit complies with its planning conditions.

What the resolution cost

The direct costs were the acoustic assessment, the relocation and enclosure works, the application fee under the national fee schedule, which is indexed annually so check the current figure, and the drawings. The indirect cost was four months of a soured relationship with the person sharing the party wall.

The version of this that costs almost nothing is doing the sequence in the other order: establish whether permission is needed, get the sound power data and check it against the distance to the nearest window, choose a position at low level away from boundaries, and tell the neighbour before the installer arrives. The same logic applies to commercial plant, and the walkthrough of a commercial extraction system and the odour objection shows how much larger the stakes get.

This is general guidance, not legal advice, and the walkthrough is illustrative rather than a report of a real decision. A lawful development certificate is the only formal way to confirm that works are lawful. Check the position with your local planning authority or a qualified professional before relying on it.

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