Air conditioning in a flat: consent, rules and your real options
Here's the thing most articles get backwards: for flats, planning permission is rarely the real obstacle — your lease is. Since the May 2025 rule changes, permitted development can cover an outdoor unit on a block of flats. But planning law only governs what the state allows; your lease governs what your freeholder allows, and fixing anything to the outside of a building you don't own the outside of almost always needs their written consent. Get that sequence right and flats are very doable. Get it wrong and you can be ordered to remove a £3,000 installation.
First, which of these are you?
| Your situation | Who you need to convince | Realistic outlook |
|---|---|---|
| Leaseholder (most flat owners) | Freeholder or managing agent, via formal consent | Achievable — with process and patience |
| Share of freehold | Your co-freeholders (often just your neighbours) | Usually easiest — it's a conversation, then paperwork |
| Renting | Landlord (who may then need freeholder consent themselves) | Fixed install rarely worth pursuing — go portable |
| Top-floor flat with private roof terrace/demised balcony | Still the freeholder — "demised" doesn't mean structural freedom | Better siting options, same consent process |
Why you can't just install and apologise later
A split system needs an outdoor unit fixed to an external wall, balcony or roof, plus a hole drilled through the structure for pipework. In almost every lease, external walls, the roof and the building's structure belong to the freeholder — they are not part of what you own, even though your flat is behind them. Installing without consent is a breach of lease, and the standard remedies run from being made to remove the unit and make good, up to forfeiture proceedings in extreme cases. It also surfaces at the worst possible moment: when you sell, the buyer's solicitor will ask for the consent paperwork, and an undocumented unit becomes a last-minute negotiation you'll lose.
The consent process (licence to alter)
Formal freeholder consent for works like this usually takes the form of a licence to alter — a short legal document recording what you're allowed to install, where, and on what conditions. The process that works:
- Read your lease first. Look for the alterations clause. "Not without landlord's written consent, such consent not to be unreasonably withheld" is the common and friendly version. An absolute bar on external alterations is rarer and harder — though freeholders can still agree voluntarily.
- Approach with a package, not a question. "Can I have AC?" invites a no. A one-page proposal — unit model and size, exact siting (rear elevation, below the parapet, on anti-vibration mounts), the MCS 020 noise assessment your installer will produce, installer's F-Gas certification and public liability insurance, and confirmation you'll cover reasonable costs — invites a yes. Freeholders say no to vagueness, not to air conditioning.
- Budget for their costs. The freeholder's solicitor and sometimes a surveyor review the proposal at your expense — typically several hundred pounds, and it can pass £1,000 for managed blocks. Annoying, standard, and worth it for paper that protects your investment when you sell.
- Expect conditions, and accept the reasonable ones. Common asks: noise limits, maintenance obligations, siting away from neighbours' windows, and reinstatement if you ever remove it. All fine. What you've bought is certainty.
Timescale: allow one to three months from proposal to signed licence for a professionally managed block; often just weeks where the freeholder is a small landlord or your fellow residents.
Where planning fits in
Separately from the lease, the May 2025 permitted development changes do extend to flats — but more tightly than houses: one outdoor unit per block (not per flat) and a smaller 0.6 m³ size limit, which still fits typical single-room condensers. Conservation areas add the no-highway-facing-elevation rule. If another resident already has a unit under permitted development, yours may need a planning application — a question your installer or the council can answer quickly. The full rules, conditions and property-type breakdown are in our planning permission guide.
What it costs and what's different about flat installs
The hardware and labour mirror any single-room split — typically £1,500–£3,500 fitted (see the full cost guide) — plus the consent costs above. Flat-specific factors installers will price on survey: condenser siting (balcony on anti-vibration mounts is the classic solution; high external walls may mean access equipment), pipe runs through communal areas being generally off-limits, and condensate drainage. Mention the floor level and balcony situation in any quote request and you'll get realistic numbers first time.
If consent is refused — or you're renting
The fallback is the one no freeholder can veto: a portable air conditioner, because it's an appliance, not an alteration. Nothing is fixed to the building, so neither the lease's alterations clause nor planning law is engaged. The trade-offs are real — more noise, more running cost, a hose to a window — and our portable vs split guide and current portable picks cover them honestly. Two flat-specific tips: pick the quietest unit you can afford (flat neighbours hear more than house neighbours), and if your windows are the tilt-or-sealed type common in newer blocks, check hose kit compatibility before buying. A leaseholder refusal is also rarely forever — freeholders change, managing agents change, and a neighbour getting consent first creates your precedent.
Ready to test the water? Size your room, then get free quotes from certified installers — say it's a flat and mention your floor and balcony situation. A written quote with unit specs and siting is exactly the document that turns a freeholder conversation into a yes.
Quick answers
Can my freeholder unreasonably refuse consent?
If your lease says consent is "not to be unreasonably withheld", a refusal must have genuine grounds — visual impact, noise risk, structural concern — not mere preference. In practice, a well-evidenced proposal (siting plan, noise assessment, insured installer) removes most legitimate grounds. If you believe a refusal is unreasonable, take advice from a leasehold solicitor before escalating; the Leasehold Advisory Service (lease-advice.org) offers free initial guidance.
Do I need consent for a unit on my own balcony?
Almost always yes. Even a "demised" balcony usually only gives you the surface, not the right to fix plant to the structure or alter the external appearance. The good news: a balcony unit on anti-vibration mounts with no wall drilling into communal structure is the easiest consent to obtain.
Can my landlord install AC if I ask as a tenant?
They can — and the winter-heating capability of a reversible unit is the argument that occasionally lands, since it upgrades their property. Realistically most won't fund it for a standard tenancy. A portable you own and take with you is the pragmatic answer for renters.
Does air conditioning add value to a flat?
Increasingly, yes — a consented, documented installation in a top-floor or south-facing flat is a genuine selling point as UK summers trend hotter. An unconsented one is the opposite: a liability your buyer's solicitor will find.