Every figure checked against its source on 7 November 2026
Air conditioning and planning permission: the rules for England
Put a reversible unit on a house, satisfy all the permitted development conditions, and no application is needed. Fit a cooling-only unit, or work on a flat over a shop, a listed building, a road-facing wall inside a conservation area or an estate whose rights were taken away by condition, and one is. The rules below are England's, with Dartford's own wrinkles marked.
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What are the permitted development conditions?
| Condition | House | Block of flats |
|---|---|---|
| Not used solely for cooling | Yes | Yes |
| Installed to MCS 020a | Yes | Yes |
| Outdoor unit volume | Up to 1.5 cubic metres | Up to 0.6 cubic metres |
| How many units | One; two if the house is detached | One per block, and only where the block is entirely flats |
| On a pitched roof | Not permitted | Not permitted |
| On a flat roof | At least one metre in from the edge | At least one metre in from the edge |
Two further conditions apply: the installer must position the unit so that, so far as practicable, it does the least harm to the appearance of the building and its surroundings, and the unit has to come down as soon as reasonably practicable once it stops being needed for heating. Since 28 May 2026 the only certification that satisfies the rule is MCS 020a. Source: Planning Portal.
Why does the word "reversible" carry so much weight?
Because the rules were rewritten for heat pumps. The amendment that took effect on 29 May 2025 replaced the old condition with one that the unit is "not solely used for the purpose of cooling", raised the volume limit on a house from 0.6 to 1.5 cubic metres and removed the rule that kept a unit a metre from the boundary. A unit that heats as well as cools can use all of that; a cooling-only unit cannot, and needs an application. Nearly every modern split is reversible, so the question is only whether the one you are quoted for is. Sources: SI 2025/560; Baxi.
What is the noise test?
Part of MCS 020a. The installer calculates the sound level the outdoor unit would produce beside the nearest door or window of the neighbouring building, taking the unit's rated noise, the distance and any reflecting surfaces into account. A result of 37 dB(A) or less meets the condition. Ask to see the calculation; it is a single sheet and it decides whether the job is permitted development at all. Source: Grant UK.
What changes in a conservation area?
Where the unit may stand. In a conservation area no wall or roof fronting a highway may carry it, and nor may any spot between the house and the road. Dartford Borough Council has six: Dartford Town Centre, Greenhithe, Southfleet, Hook Green, Church Hill in Wilmington and Red Street. Bexley has 23, nine of them in Sidcup alone, and Gravesham's town-centre and suburban areas carry Article 4 directions as well. Away from conservation areas, a wall that faces a road may take a unit at ground-floor level only.
Sources: Planning Portal; Dartford Borough Council; Bexley Council; Gravesham Borough Council.
What about a new estate?
Check two documents before the survey. The first is the planning permission the estate was built under: councils sometimes attach a condition removing permitted development rights, so that every later change needs an application, and Dartford has added thousands of new homes since 2011. The second is the deeds or the management company's covenants, which may restrict what can be fixed to the outside of the house regardless of what planning allows. Neither is unusual at Ebbsfleet or on the newer streets at Stone and Swanscombe, and both are cheaper to read than to discover afterwards. Sources: Planning Portal; ONS.
What does an Article 4 direction do?
It removes particular permitted development rights in a defined area, so that work which would normally be allowed needs an application. Dartford's register lists five older directions, among them the Greenhithe conservation area, two stretches of West Hill and Darenth Wood at Bean; on shared houses, one direction has applied north of the A2 since December 2025 and another takes effect south of it on 10 December 2026. Gravesham's directions cover windows, doors and other features in its conservation areas; Bexley's cover shared houses across the borough and commercial premises turning into homes in 13 town centres. A direction on shared houses does not stop an outdoor unit, but one over a conservation area may. We check before quoting. Sources: planning.data.gov.uk; Dartford Borough Council; Gravesham Borough Council; Bexley Council.
What about listed buildings and business premises?
A listed building needs listed building consent for any work that affects its character, and doing it without consent is an offence; planning permission does not stand in for it. Historic England's draft advice of 2023 was that heat pumps on listed buildings will generally be acceptable where they are sympathetically sited, which is not the same as not needing consent. For a shop, office or other non-domestic building, the Planning Portal says a heat pump is likely to need an application, and a July 2026 legal review notes that an enforcement notice can require a unit to be removed. Our air conditioning in Dartford page sets out the local picture. Sources: section 7; section 9; The Construction Index; Planning Portal; Mishcon de Reya.
Questions people ask
My neighbour already has a unit on our block. Can I?
Not as permitted development: the allowance is one unit per block. You can apply for planning permission, or look at a unit with no outdoor box.
Does a detached house really get two?
Yes, since May 2025, each up to 1.5 cubic metres and each passing the noise test. A multi-split may still do the same job with one.
Who checks all this?
We do, at the survey, and the sound calculation goes in your file. If an application is needed, we prepare the drawings; you or your agent submit it.
Sources we checked
- Planning Portal: when an air source heat pump on a house or flats is permitted development
- legislation.gov.uk: the 2025 amendment to the permitted development order (SI 2025/560)
- Baxi: what changed for heat pump permitted development on 29 May 2025
- Grant UK: planning guide for heat pumps in England, with the 37 dB(A) test (May 2025)
- Dartford Borough Council: the borough's conservation areas
- Bexley Council: conservation areas, listed buildings and historic parks
- Gravesham Borough Council: Article 4 directions, a guide for owners (April 2020)
- ONS: how the population changed in Dartford, Census 2021
- planning.data.gov.uk: Dartford's Article 4 directions
- Dartford Borough Council: Article 4 directions for houses in multiple occupation
- Bexley Council: Article 4 directions in force
- legislation.gov.uk: section 7 of the Listed Buildings Act 1990
- legislation.gov.uk: section 9 of the Listed Buildings Act 1990
- The Construction Index: Historic England's draft advice on heat pumps and listed buildings (November 2023)
- Planning Portal: air source heat pumps on non-domestic buildings
- Mishcon de Reya: the legal checks before installing air conditioning (8 July 2026)
Worth knowing before you ring
With these we can usually tell you on the first call whether the job is simple.
- The postcode
- Whether it is a house, a flat or business premises, and roughly its age
- If you rent or lease, who owns the external wall
- Which room, how big, and the direction its window faces
- Any management company, conservation area or listing that applies
Decided? Our air conditioning in Dartford page covers what we install, what we maintain and where we go.
The services this guide leads to
Air-to-air heat pumps
The same wall unit, run the other way: a room heated for pence an hour, with the summer cooling thrown in.
Air conditioning installation
The whole job from the first measurement to the handover of the remote, with every consent checked on the way.
Commercial air conditioning
Retail and hospitality premises, sized with the door open and the bedroom over the shop remembered.
Other guides
What does air conditioning cost to fit and to run?
Where the money goes: the unit, the labour, the wiring, the electricity, and the extras a flat or a new estate brings.
Air conditioning with no outdoor unit: how monoblocs work
The through-the-wall units for flats and blocks that cannot take an outdoor box.
Air conditioning in a flat: who has to agree, and in what order
Lease, freeholder, management company and planning, in the order to tackle them.
Bedroom air conditioning: what it does for sleep, and what it costs
The sleep threshold, noise at night, sizing and the price of a quiet bedroom.
Cooling a loft conversion: the options that work
Why lofts cook, the free fixes first, then where a unit goes on a dormer.
What size of air conditioner does a room need?
Kilowatts and BTU by room size, with the adjustments that matter.
How to check an air conditioning installer on the F-gas register
The company certificate, the engineer's category and where to look them up.
Portable or fixed air conditioning: which is right for you?
Price, power, noise and running cost, and when a portable is the right call.
Want us to ring you?
A name, a number and a postcode is enough. Say which room if you can. Or ring 01322 952910.