Can a flat in a conservation area have an outdoor unit?
For a flat in a conservation area the outdoor unit is usually permitted development on a wall that does not face a highway, if the building is wholly flats and the unit is within 0.6 m³ (Class G, G.2(j), checked 25 Sep 2026). If that wall or the roof faces a highway, Class G does not cover it.
computed
Worked case from the decision engine
Result on the facts named above: permitted development.
The worked case enters a building that is wholly flats, one unit, volume 0.5 m³, conservation area yes, wall and roof not facing a highway, noise entered as a pass. Wales uses 1 m³ for a block of flats, not 0.6 m³.
Volume, noise and listing in the worked case are entered facts. They are not read off the postcode.
Cooling paths
At 400 hours and the Ofgem cap, the split scenario is £27.71 and the portable scenario delivering the same 2.5 kW is £101.23.
| Path | What it is | Up front | £ for 400 h | Open |
|---|---|---|---|---|
| External shading | No outdoor unit | Shelf prices sit in the shade class of the retail file | No compressor draw in the catalogue | /tools/sizing/ |
| Fan | Devola Low Noise 20W 9 Speed 9-inch DC Desk Fan - White - DVF7DCFAN | £59.95 | £2.11 for 400 h at 20 W | /tools/running-cost/ |
| Portable | Cirro® 12000 BTU Super Quiet Smart Portable Air Conditioner - Cooling | £519.99 | £101.23 to deliver 2.5 kW for 400 h at EER 2.6 | /tools/running-cost/ |
| Split / air-to-air | Daikin Perfera 2.5 kW, SEER 9.5 | median shelf £1,027.49 (n=14) | £27.71 for 400 h | /tools/payback/ |
The clauses this situation turns on
ENG-10 · G.2(j) · checked 25 Sep 2026. in the case of land within a conservation area or which is a World Heritage Site the air source heat pump—(i) would be installed on a wall or a roof which fronts a highway; or (ii) would be installed so that it is nearer to any highway which bounds the curtilage … nearest to that highway Source
ENG-14 · interpretation, ‘block of flats’ · checked 25 Sep 2026. “block of flats” means a building which consists wholly of flats Source
ENG-05 · G.2(d), as substituted by SI 2025/560 art. 5(3)(b) · checked 25 Sep 2026. the volume of the air source heat pump's outdoor compressor unit (including any housing) would—(i) … a dwellinghouse, exceed 1.5 cubic metres; (ii) … a block of flats, exceed 0.6 cubic metres Source
ENG-01 · Class G, permitted development · checked 25 Sep 2026. The installation, alteration or replacement of a microgeneration air source heat pump—(a) on a dwellinghouse or a block of flats; or (b) within the curtilage of a dwellinghouse or a block of flats, including on a building within that curtilage. Source
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· · n= · · updated 25 Sep 2026 · version 1.0.0 · CSV of the values on this page