Domestic wind turbines and the Class H limits

A domestic wind turbine can be permitted development, and the limits are tight enough that most installations on an ordinary house will not fit inside them. Class H of Part 14 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015 covers a turbine installed on a dwellinghouse or a building within its curtilage, with a companion class dealing with a standalone turbine on the ground. Both cap the swept area, control the height and require that the property does not already have an air source heat pump or another turbine.

That last condition catches more people than any dimension. A house that installed an air source heat pump two years ago has used up the right.

What Class H of Part 14 permits

The class allows the installation, alteration or replacement of a wind turbine on a dwellinghouse, or on a building within the curtilage of a dwellinghouse, subject to limits and conditions. A separate class in the same Part covers a standalone turbine within the curtilage, with its own and slightly more generous height limits.

Read the current text of Part 14 on legislation.gov.uk before relying on any figure quoted anywhere, including here. The Order has been amended repeatedly since 2015 and the renewable energy Part has had more changes than most.

The structure of the controls is consistent across both classes:

• A cap on the swept area of the blades.
• A height limit, expressed relative to the roof for a building-mounted turbine and as an overall height for a standalone one.
• A minimum clearance between ground level and the lowest part of the blade.
• A separation distance from the boundary of the curtilage.
• A limit of one turbine, with no air source heat pump already installed.
• A requirement that the installation complies with the applicable microgeneration certification scheme planning standards or equivalent.

Height, blade and siting limits

For a turbine mounted on a building, the limit is framed as blade tip height measured against the highest part of the roof excluding the chimney, with an absolute ceiling expressed above ground level, and the lower of the two applies. For a standalone turbine the control is an overall height above ground level.

The swept area cap is the one that usually decides whether a turbine of any useful output can be installed within permitted development. Small roof-mounted machines fall inside it comfortably. Anything with a rotor large enough to generate meaningful output on an inland site generally does not.

Siting limits do the rest of the work. A minimum clearance under the blades and a minimum distance from the curtilage boundary mean that a small or narrow garden cannot accommodate a standalone turbine at all, and a terraced or semi-detached house is unlikely to meet the boundary distance for a building-mounted one.

Measure before you specify. The clearance is measured to the lowest part of the blade, which on a three bladed turbine is the bottom of the rotor sweep rather than the hub.

Only one turbine and the air source heat pump interaction

The condition is cumulative across technologies. The right is not available where the dwellinghouse or the building already has a wind turbine, and it is not available where it already has an existing air source heat pump installed under the equivalent class in the same Part.

The logic is about the aggregate visual and noise effect of domestic microgeneration equipment on a single property, and in practice it means a choice has to be made. A household going down the heat pump route and later wanting a turbine will need a full planning application for the turbine, and the reverse is equally true.

The sequencing point matters for anyone planning a package of measures. Decide the whole strategy first, because the order of installation determines which items keep their permitted development route. Borehole-based systems sit in a different class with different consent issues, which ground source heat pumps and borehole permitting deals with.

Conservation areas, listed buildings and safeguarded land

The exclusions remove the right in the settings where visual effect matters most. A turbine on a listed building or within its curtilage is outside the class and needs both planning permission and listed building consent for any works affecting the listed structure.

Conservation areas and World Heritage Sites are treated restrictively. Safeguarded areas around aerodromes and defence establishments are also excluded, because a rotating blade is an aviation and radar issue as well as a planning one.

Where any of those apply, the route is a full application, and the case is made on the ordinary design and amenity tests. On a rural holding outside a designation the picture is different again, and the limits for larger agricultural turbines work on a separate basis, as farm wind turbines and permitted development limits explains.

Noise assessment expectations

Noise is the issue that generates complaints about domestic turbines, and the mechanism is specific: mechanical noise from the generator and gearbox transmitted through the mounting structure, plus aerodynamic noise from the blades.

For a building-mounted turbine, structure borne transmission into the building it is fixed to is often the dominant effect. A turbine bolted to a gable wall puts vibration into the structure, and the bedroom behind that wall is the receptor nobody assessed.

Within permitted development, the microgeneration certification scheme planning standards include a noise assessment method, and compliance with those standards is a condition of the right. Where a full application is needed, authorities commonly ask for an assessment of noise at the nearest neighbouring dwelling. The method used for large wind farms is not designed for a single domestic machine, so expect a simpler approach based on the manufacturer's sound power data with distance attenuation, and a comparison against background levels at the nearest window.

Ask the supplier for sound power level data at the wind speeds where the turbine actually operates rather than a single headline figure. A Noise Impact Assessment built on one number at one wind speed will be sent back.

Shadow flicker and separation distances

Shadow flicker is the strobing effect produced when a rotating blade passes between the sun and a window. National guidance on renewable energy indicates that it occurs only within ten rotor diameters of a turbine, which for a small domestic machine is a short distance, and that is the reason it rarely troubles domestic applications.

Where a window does sit within that range, the assessment is geometric: the sun path through the year, the position of the rotor, and the windows affected. Mitigation is usually repositioning, or in persistent cases a control system that shuts the turbine down during the affected periods.

Separation from neighbouring dwellings also addresses the general amenity question of a moving structure in close view, which is a separate matter from either noise or flicker and is judged rather than measured.

An illustrative example

A detached house on a one acre rural plot outside any designation considers a standalone turbine. The garden offers a position meeting the boundary separation, but the household installed an air source heat pump three years ago, so the permitted development right is not available. A full application is made instead, supported by a noise assessment using the manufacturer's sound power data, a shadow flicker check for two windows within range, and a statement on visual effect in the wider countryside. This example is illustrative and not a prediction of any decision.

When a full application is unavoidable

Four situations put a domestic turbine outside the permitted development route, and recognising them early saves a wasted enforcement conversation:

1. The property already has an existing air source heat pump or a turbine.
2. The site is in a conservation area or World Heritage Site, or the building is listed, or the land is safeguarded.
3. The machine exceeds the swept area or height limits, which is common for anything with useful output.
4. The siting cannot meet the clearance or boundary distance.

A full application is not a bad outcome. It allows a larger machine, which on many sites is the only way the economics work, and it produces a permission that is not vulnerable to an argument about whether a limit was met.

Where energy performance is part of a wider scheme, the turbine belongs in an Energy Statement with the rest of the strategy rather than as a standalone item, so the officer sees the whole picture.

This is general guidance, not legal advice. The limits in Part 14 have been amended several times, so check the current text of the Order and the position with your local planning authority before relying on it. A Lawful Development Certificate is the only formal way to confirm that an installation is lawful.

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