Putting an outdoor unit on a flat balcony is one of the hardest domestic installs in the UK. You may be fixing to a slab you do not own, dripping on the flat below, blocking an escape route, and facing a highway. Class G can apply to a block of flats in England, with a tighter outdoor volume cap and only the first installation treated as permitted development, but balconies often fail those limits or the highway rules. The lease can say no even when the council would not. Survey structure and consent before you choose an indoor. F-gas work comes after that.
A glass Juliet asked to carry a condenser
Outdoor units are heavy, they vibrate, and they need airflow on several faces. A glass Juliet balcony or a thin deck with a pretty balustrade may not be a place to stand one. Ask who owns the slab and whether a structural check is required before anyone promises a bracket.
Water on the flat below, and a path for the engineer
Condensate and defrost water must not pour onto the balcony below or down the facade. A pump or a proper drain is part of the survey. So is service access: an engineer has to reach the unit without climbing over your furniture every summer.
- Check ownership of the slab and the balustrade.
- Do not block a fire escape or a common walkway.
- Manufacturer clearances still apply in a tight balcony.
The 0.6 cubic metre cap on a block of flats
On the Planning Portal's current Class G summary, the outdoor compressor housing on a block of flats must not exceed 0.6 cubic metres, and only the first installation is permitted development. Detached houses are treated more generously. Highway-facing walls have their own limits, and many balconies are exactly that elevation. Legislation.gov.uk is the Class G text.
The unit must not be used solely for cooling if you are relying on that permitted development. Listed buildings, conservation areas and Article 4 directions add further reasons to apply. Often a balcony job needs permission. Sometimes a discreet well-sited first unit does not. Do not generalise from one block to the next. Energy Saving Trust describes air-to-air heat pumps. That description is separate from whether this balcony is allowed.
A council letter that does not amend the lease
Freeholders and managing agents regularly ban external plant, balcony storage and anything fixed to the facade. Written consent, sometimes a licence to alter, is the document that matters. A council letter saying permission is not required does not amend the lease.
If the balcony is refused, a through-wall monobloc still needs holes in an external wall, which is also usually a lease matter. It is quieter outside and noisier inside. It is not a secret route around the freeholder.
Stop if the slab, the escape route or the lease is open
Photos of the balcony, the slab edge, the flat below if you can see it, and the elevation from the street are the survey record. Say whether the balcony is an escape route. Name the floor. Ask the installer to pause if the lease is unsigned. GOV.UK F-gas commissioning is the last step, not the first. The balcony does not change refrigerant law. A competent firm will talk about consent and structure before a designer fascia.
Frequently asked questions
Is a balcony condenser always illegal?
No. Some are acceptable with consent, a sound fixing and a lawful planning position. Many fail the lease, the structure, the highway test or the volume cap. Treat it as unproven until this block has been checked.
Can I stand the unit on rubber feet so it is not fixed?
An unfixed unit that can vibrate into a glass balustrade is not a clever exception. It can be more dangerous, and the lease may still forbid plant on the balcony. Ask before you improvise.
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How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.