Permitted Development: Solar on a Roof and Heat Pumps at a Boundary

A neighbour wants an air source heat pump a metre from the fence. An older textbook says that is not permitted development. A current one says it is. Both were right when they were printed.

The short answer

Permitted development means the installation can go ahead without the need for planning permission — the right is granted in advance, subject to conditions, so no application is made.

It is a right, not an exemption from everything else. The Climate Change and Sustainable Energy Act 2006 brought micro-renewables within the Building Regulations, so even where no planning application is needed, the relevant Parts still apply in full.

And three situations are never permitted development, whatever else changes: listed buildings, scheduled monuments, and areas covered by an Article 4 direction. A conservation area is not one of them: the right survives there, with conditions.

Where the right comes from

The right comes from the Town and Country Planning (General Permitted Development) Order — the GPDO — which is amended periodically. Published guidance and textbooks lag behind those amendments, which is why older material can be confidently wrong.

Planning is also devolved: Scotland, Wales and Northern Ireland each have their own order, so check the one for the country you are working in.

Two practical points follow. The local planning authority is the arbiter — not the certification body, not building control, not environmental health. And where a customer wants certainty in writing that the work is lawful without permission, the document is a lawful development certificate.

For solar on a listed building, planning consent is always required — not only if the panels face the road, not only above a certain number, and not only if the roof is thatched.

The solar conditions

For a building mounted system on a house, the order sets a figure for each position:

• On a pitched roof: not more than 200 mm beyond the roof slope, and not above the ridge, excluding the chimney.
• On a flat roof: the highest part not more than 600 mm above the highest part of the roof.
• On a wall that abuts a highway: not more than 200 mm beyond the plane of the wall.
• On any other wall: not more than 400 mm.

Do not carry the 200 mm across to all four. A flat roof has had its own 600 mm since 21 December 2023, and the wall figures above are a house’s from 27 August 2026 (SI 2026/896). A block of flats keeps 200 mm on every wall; its roof figures are the same as a house’s.

For a standalone system in the grounds of a house, SI 2026/896 rewrote the rules from 27 August 2026. The panels must be not more than 9.0 m², and the height is the lowest limit that applies: 4.0 m normally, 2.0 m within 5.0 m of the boundary, and 1.0 m within 5.0 m of the boundary and in front of the house. There is no limit on the number of arrays, or on any one dimension.

Much published material still prints the rules before 27 August 2026, which still apply to a block of flats: one only; not more than 4.0 m high; at least 5.0 m from the boundary; not more than 9.0 m² in area; and no dimension over 3.0 m. Beside a house, being within 5.0 m of the boundary is no longer a bar — it is what lowers the height.

On a world heritage site a standalone array must not stand nearer a highway than the house, nor within 5.0 m of the boundary. In a conservation area it may: since 21 December 2023 (SI 2023/1279), one nearer a highway than the house is limited to 2.0 m, and a prior approval application about its appearance must go to the local authority first. Since 27 August 2026 an array within 5.0 m of the boundary needs the same application there, or anywhere else on article 2(3) land, such as a National Park. Exam questions may still give the older rule that a standalone array in a conservation area is not permitted development, or must not stand nearer the highway than the house; the order said the second until 21 December 2023.

Water conservation systems are treated more gently. Rainwater harvesting and greywater re-use do not generally need planning permission where the external appearance is unaltered. Ask the authority where the tank is above ground, or the property is listed or in a designated area — and remember that if a building is put up to house the plant, that building needs permission in its own right.

Two habits keep you out of trouble. Record on the survey which order you checked and when, because the conditions are amended and last year's note is not evidence about this year's rules. And where the customer needs certainty in writing, apply for the lawful development certificate rather than relying on anybody's opinion, your own included.

Heat pumps: the rules moved

The position in England, as at August 2026, is that:

• The 1 m from the boundary rule has been removed.
• A volume limit of 1.5 m³ applies to the outdoor unit.
• Two units may be installed on a detached house.

Much published material, and many older exam papers, still print the previous position: one unit only, a 0.6 m³ volume limit and a 1 m separation from the boundary. Recognise it for what it is — the old rule — and check the current order.

One 1 m rule does survive, and it is easy to confuse with the one that went: where a unit is installed on a flat roof, it must be at least 1 m from the external edge of that roof. A different measurement, to a different thing, for a different reason.

Noise

Noise is what most of the conditions are really about. The assessment is made 1 m out from the centre of any door or window to a habitable room of a neighbouring property — a neighbour's opening, and a habitable room such as a bedroom or living room, rather than the boundary line or a point one metre from the unit. Read that carefully: any such opening, not just the nearest, and a door counts as well as a window. The limit is 37 dB L_Aeq,5mins under MCS 020 a). Do not confuse it with 42 dB: that is MCS 020 b), the wind turbine version, and it was also the figure in the single MCS 020 that covered both before the two were split.

Passing the assessment does not close the subject. Noise from an installed heat pump can still be pursued as a statutory nuisance by the local authority, whatever the planning assessment concluded. They are two separate regimes, and passing one does not immunise you against the other.

In practice that means the siting decisions matter as much as the paperwork: distance from windows, anti-vibration mounts, and never fixing the unit rigidly to the house wall.

And it shapes the quotation as well as the form. A position that satisfies the assessment on paper can still be the wrong one for the household: a unit under a bedroom window may be within the rules and outside common sense. Say at survey where the unit will stand and why, so the customer hears the reasoning before the machine arrives rather than after it starts running.

A conservation area is a difficult place for an air source unit, but the right survives there: the unit may not go on a wall or roof that fronts a highway, or anywhere nearer a highway than the house, and a world heritage site is treated the same way. A ground source installation raises fewer planning difficulties there for one reason: the collector is buried and the heat pump itself is indoors, so there is no visual impact — and visual impact is precisely what conservation area control is about. It is not because groundworks are permitted development in every circumstance, and not because ground source is exempt from planning control.