Air conditioning units on a house or flat: the planning rules

An external air conditioning condenser on a house in England will usually need planning permission, and on a flat it almost always does. There is no permitted development class written for air conditioning, so the question splits in two: does fixing the unit to the building count as development, and if it does, is there a class that covers it. Most householders find the answer is an application, a sound data sheet and a drawing showing exactly where the box sits.

That catches people out because air source heat pumps do have their own permitted development class and air conditioning does not, even though the hardware looks similar from the street.

Whether the unit is development at all

Section 55 of the Town and Country Planning Act 1990 defines development to include building operations, and alterations count. The useful exclusion is in section 55(2)(a)(ii): works that affect only the interior of a building, or that do not materially affect its external appearance, are not development.

A small condenser tucked at the rear of a two-storey house, below eaves level and invisible from any public vantage point, can sit within that exclusion. A pair of units bracketed to a front bay window does not. Between those extremes sits a judgement call, and the judgement belongs to the council rather than to the installer who tells you it is fine.

If you want certainty, a lawful development certificate under section 192 of the 1990 Act is the formal route. It costs a fee and takes eight weeks, and it is the document that actually binds the authority.

Permitted development, and why flats have none

Part 1 of Schedule 2 to the General Permitted Development Order 2015 gives householders rights to enlarge, improve or otherwise alter a dwellinghouse. A wall-mounted condenser can be argued as an alteration within Class A, subject to every limitation in A.1 and the conditions in A.3, including the requirement that materials be of similar appearance to the existing house. Councils vary in how readily they accept that argument, and some set out their position in a householder design guide.

Part 1 does not apply to flats. The definition of dwellinghouse in the Order excludes a building containing one or more flats and a flat within such a building, so there are no householder rights to rely on. Any external alteration to a flat needs permission unless it falls outside section 55.

Part 14 Class G is the air source heat pump class, and it does extend to a block of flats as well as a house. Its limits on unit volume, siting and compliance with the relevant microgeneration planning standard have been amended more than once, so check the current text of the Order rather than an older summary. A reversible heat pump installed to provide heating is a different proposition from a cooling-only condenser, and the paperwork should say which it is.

Where the unit can go

Siting decides most of these applications. Officers look at three things: whether the unit is visible from the street or a public footpath, whether it sits close to a neighbour's window or garden, and whether it reads as clutter on the elevation.

Ground-mounted units on an anti-vibration plinth, set behind a slatted timber screen, cause far fewer problems than wall brackets. The screen has to allow the airflow the manufacturer specifies, so take the clearance dimensions from the technical manual and show them on the plan.

Noise to the nearest window

This is where applications are won or lost. The council's environmental health team will want to know the sound pressure level at the nearest noise-sensitive window, usually a habitable room window in a neighbouring property, and how that compares with the existing background level.

Start with the manufacturer's sound power level in decibels, then calculate the level at the receptor allowing for distance, directivity and any reflecting surfaces. Where the unit will run at night, the night-time background matters more than the daytime figure, because the margin between plant noise and a quiet 3am background is what generates complaints. Planning Practice Guidance on noise sets out the significant observed adverse effect level framework that officers apply.

Conditions commonly require the rating level to sit at or below the background level, measured in accordance with the recognised method for industrial and commercial sound. For a single domestic condenser that is often achievable with a low-noise night mode, careful siting and an acoustic louvre. For three units serving a large house it may not be, and an honest Noise Impact Assessment will say so before the application goes in rather than after a refusal. Expect a condition fixing the limit, and treat it the same way you would treat an obscure glazing condition on a side window: it binds you and your successors.

Separately from planning, noise that unreasonably interferes with a neighbour's enjoyment of their home can be a statutory nuisance under Part III of the Environmental Protection Act 1990. A planning permission is not a defence to that.

Conservation areas and listed buildings

In a conservation area, external alterations visible from a public place attract much closer scrutiny, and an Article 4 direction may have removed the householder rights you would otherwise rely on. Check the council's constraint map before designing anything.

For a listed building, listed building consent is needed for works affecting character as a building of special architectural or historic interest, and that includes a condenser fixed through historic brickwork or a flue-like intervention on a principal elevation. Consent and planning permission are separate applications with separate tests. The same care applies to other external interventions, which is why removing a chimney stack in a conservation area is rarely as simple as it sounds.

Where heritage is engaged, a short Heritage Statement explaining significance, the harm the unit causes and why a less harmful position is not workable does more than a plan on its own.

Alternatives with fewer constraints

Passive measures first, because they need no permission and no electricity: external shutters or blinds on south and west glazing, solar control film, cross ventilation, insulated loft and a lighter roof finish. Approved Document O of the Building Regulations now requires new dwellings to limit overheating, and the same hierarchy works on an existing house.

Beyond that, a comfort cooling system with the condenser inside a ventilated roof void or garage, ducted to grilles, removes the external box altogether. It costs more and loses some efficiency. And it avoids the argument.

What to submit if you apply

• A householder application with a location plan and a block plan at a recognised scale.
• Existing and proposed elevations showing the unit, its brackets or plinth and any screen, dimensioned.
• The manufacturer's data sheet with sound power levels for the operating modes you intend to use.
• A short noise calculation identifying the nearest noise-sensitive window and the distance to it.
• Photographs of the proposed position and of the neighbouring windows that face it.
• A note on hours of use if you are willing to accept a restriction.

Officers refuse these applications for a short list of reasons: no noise evidence at all, a unit on a visible elevation, and a position so close to a boundary that no mitigation can work. Each one is avoidable at design stage.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and remember that a lawful development certificate is the formal way to confirm that works are lawful without permission.

If you are putting the application together, enter your postcode on PlanScope to see which supporting documents the site is likely to need.

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