The short answer for most Kent homes is “probably not, but check anyway.” The longer answer involves permitted development thresholds, conservation areas, listed buildings, the difference between mono-splits and multi-splits, and what happens when your neighbour decides to object. This guide walks through the rules as they stood at the start of 2026, what the seven Kent planning authorities actually enforce, and the practical design choices that keep most jobs out of a formal application altogether.
1. Permitted development — the domestic baseline
Under the General Permitted Development Order, a homeowner in England can install air conditioning without planning permission if all of these are true:
- The outdoor unit (condenser) volume is 0.6 m³ or less
- The unit is mounted at least 1 m from any boundary
- The unit is not on a wall facing a highway if the property fronts a road
- The unit is not on a roof or chimney
- The property is not in a conservation area
- The property is not listed
- The unit is removed when no longer required
A typical residential single split (Mitsubishi MSZ-AP35, Daikin FTXM35) has an outdoor unit around 0.15 m³ — well under the 0.6 m³ ceiling. Multi-splits with two indoor units typically use a slightly larger outdoor unit but still inside permitted development. Three- and four-zone systems push toward the threshold; five-zone units typically exceed it.
2. Conservation areas in Kent — the big exception
Conservation areas remove permitted development for external plant. The conservation areas we encounter most often:
- Sevenoaks Town — covers the High Street, Vine, Old House, plus several residential streets
- Westerham — the whole town centre and significant surrounding residential
- Otford — village centre plus High Street
- Tonbridge Castle area — immediately around the castle and along the High Street
- Royal Tunbridge Wells — multiple conservation areas covering most of the historic town
- Penshurst, Chiddingstone, Edenbridge — village conservation areas
If you’re in any of these, even a small side-elevation outdoor unit needs planning permission. The application is a householder one (Form 1A in Sevenoaks DC’s system), with a £258 fee and 6–8 week determination. We routinely submit these on clients’ behalf as part of the install package.
3. Listed buildings
Listed buildings need both planning permission and Listed Building Consent (LBC). LBC is the harder approval — you’re asking permission to alter a building of special architectural or historic interest. The approach that gets approved:
- Concealed indoor units — cassette or ducted, hidden in ceiling voids; not the visible wall-mounted box
- Refrigerant routing through existing wall holes or via service-duct routes that don’t require new fabric penetrations
- Ground-mounted condenser at the back, screened by planting or a discreet timber surround
- Reversible install — documentation showing how the system could be removed without permanent alteration
A typical listed-building AC install through to commissioned system runs £6,000–£12,000 and 6–9 months from first survey to switching on, depending on how the LPA responds.
4. The pragmatic side-elevation install
For 80% of Kent homes, the standard install — outdoor unit on the side or rear elevation, 1.5–2 m above ground, 1.5 m from the boundary, neat refrigerant pipe route — sits inside permitted development. No application, no fee, no neighbour notification. What we always do at survey:
- Measure the outdoor unit volume against the 0.6 m³ threshold
- Confirm boundary distances with a tape, not an estimate
- Check the property online against the conservation-area and listed-building registers
- Note any neighbour overlooking concerns that might trigger a complaint
Even when no planning is needed, we still write the install up properly — F-Gas logbook, refrigerant charge, commissioning data. That paperwork matters if the property sells later and a buyer’s solicitor asks “was planning needed for the AC?”
5. Commercial installs in Kent
Commercial permitted development rules are looser than domestic in some respects, tighter in others. The headline thresholds for shops, offices and similar:
- Single condenser unit up to 1 m³ volume
- At least 1 m from any boundary
- Not on a wall fronting a highway
- Not on a roof unless the property is over 4 stories
Larger units, VRF condensers serving multiple zones, and any rooftop plant on lower buildings need planning. So do most installs in high-street conservation areas (Sevenoaks High Street, Tonbridge High Street, Tunbridge Wells Pantiles).
6. Noise — the real complaint vector
Even where planning isn’t needed, noise complaints are. Modern condensers run at 48–52 dB(A) at 1 m — quieter than ambient daytime road noise in most Kent streets. But siting matters:
- Avoid mounting on the boundary side closest to a neighbour’s bedroom window
- Use anti-vibration mounts on cavity walls
- Consider a sound jacket on units within 3 m of a habitable neighbouring room
- Schedule night-mode operation (most modern AC supports a -3 to -5 dB night setting)
We do a noise assessment at survey for any install within 3 m of a neighbour’s habitable space, and design out problems before the install rather than after the complaint.
7. Pre-application advice — worth the £250
Every Kent planning authority offers paid pre-application advice. For about £200–£400 you get a written officer response telling you whether your proposal is likely to be approved. For listed buildings and conservation areas this is essentially mandatory — submitting a full application without it usually gets you a refusal you could have avoided.
8. What we handle as part of the install
For Kent clients who need planning, we typically include in the install quote:
- Site assessment against permitted-development criteria
- Conservation-area / listed-building check via the LPA register
- Pre-application advice request and response review
- Drawings and photos for the formal application
- The planning application itself (you sign as applicant, we submit and manage)
- Liaison with the case officer through to determination
Get the planning right at the start; the install is the easy bit.