Solar panels on a pitched roof and the projection limit

The solar panel projection limit roof rule is 200 mm. Under Class A of Part 14 of Schedule 2 to the General Permitted Development Order 2015, solar photovoltaic or solar thermal equipment on a house is permitted development provided it does not protrude more than 200 mm beyond the plane of the roof slope, and provided no part of it stands higher than the highest part of the roof, excluding any chimney. On a standard pitched roof with in-plane or low-profile mounting, that is comfortable. On a shallow pitch with tilt frames, it is not.

Two further conditions apply whatever the geometry: the equipment must be sited, so far as practicable, to minimise its effect on the external appearance of the building and the amenity of the area, and it must be removed as soon as reasonably practicable when no longer needed.

Measuring the 200 mm

The measurement is from the plane of the roof slope to the outermost part of the installation, and the outermost part includes the frame and any fixing that projects, not just the panel face.

Where this goes wrong:

• Tilt frames on a shallow pitch. Raising panels to improve the angle on a 15 degree roof will normally break the limit at the high edge.
• Mounting rails on uneven tiles. Pantiles and deep profile concrete tiles need standoffs, and a deep rail plus a standoff can use most of the allowance before the panel is fitted.
• Optimisers and isolators fixed on the roof rather than inside.
• Bird protection mesh added later, which is usually within the limit but should be checked against the installed projection rather than the panel depth alone.

Ask the installer for the installed projection dimension in writing, measured from the roof plane to the highest point of the assembly, before the work is booked. That single figure is the one an enforcement officer would measure.

The ridge condition

No part of the equipment may be higher than the highest part of the roof, chimneys excluded. On a simple gable roof that means nothing may break the ridge line.

Three situations need care. A panel array on the upper part of a shallow pitch, where the frame carries the top edge above the ridge. An installation on a lower flat-roofed extension where the measurement is taken against that roof rather than the main house. And a hipped roof where the highest part is a short ridge, so the reference line is lower than people assume.

Where the installation would break the ridge, planning permission is required for the whole installation rather than just the offending panel, so the design usually moves rather than the application being made.

Siting to minimise the effect on appearance

This condition is often treated as decorative wording. It is not, and it is the condition an authority is most likely to rely on if it takes issue with an installation.

The requirement is to site the equipment so far as practicable to minimise effect on the external appearance of the building and on the amenity of the area. Practicable allows for solar performance, so an installation on a rear roof slope facing north when the south-facing front slope is the only viable orientation is unlikely to be expected. But an array spread across a front elevation when a rear slope would have produced a comparable yield is vulnerable.

Practical steps that keep an installation defensible:

1. Choose in-plane mounting over tilt frames where the pitch allows.
2. Use all-black panels and dark frames on dark roofs, and keep the array to a rectangular block rather than a scattered layout.
3. Set the array back from ridge, eaves and verge so a margin of roof covering remains visible.
4. Keep cable runs and isolators inside the roof space or on a rear elevation.
5. Record the yield comparison between the chosen slope and the alternatives, so the practicability judgement can be evidenced if questioned.

Step five costs nothing at the design stage and is the answer to a complaint two years later.

Designated land and listed buildings

On what the Order calls article 2(3) land, which covers conservation areas, National Parks, National Landscapes, the Broads and World Heritage Sites, the right does not permit installation on a wall forming the principal elevation where the equipment would be visible from a highway. Roof installations remain possible, subject to the general conditions, and the appearance condition carries more weight in these areas in practice.

Listed buildings are a separate matter. Listed building consent is required for works affecting the character of a listed building, and an installation on a principal roof slope will normally be resisted where it is visible in important views. Consent is more likely on a rear slope, an outbuilding roof or a ground-mounted position screened from public view, supported by a short Heritage Statement explaining the effect on significance and why alternatives were rejected.

An Article 4 direction can also withdraw Part 14 rights, so check the position for the address rather than assuming that only conservation area designation matters.

The removal condition

The right is conditional on the equipment being removed as soon as reasonably practicable when no longer needed for microgeneration.

In practice nobody enforces this against a working system, and it matters in two situations. Where an array has been disconnected and abandoned, leaving redundant panels and frames on a roof, the authority can require removal. And on sale, a buyer's surveyor asking about a dead system raises a question that is easier to answer with a decommissioning record than with a shrug.

Keep the commissioning certificate, the inverter warranty and the installer's details with the property papers. They also evidence the installation date, which matters if the lawfulness of the installation is ever questioned.

Flat roofs and stand-alone installations

Flat roofs are the awkward case. The 200 mm allowance is measured from the plane of the roof, and any framing that tilts panels to a useful angle on a flat roof will exceed it. Installations on flat roofs therefore frequently need planning permission, and the application is usually judged on visibility from the street and from neighbouring windows.

A separate class in Part 14 covers stand-alone solar equipment within the curtilage of a house, and its limits are different in kind:

Read the current text of that class for the figures, because Part 14 has been amended several times and the limits for stand-alone equipment differ from the roof-mounted conditions. A ground-mounted array in a rear garden is often the better answer on a sensitive building, since it keeps the roof unaltered.

Where an application is needed, and what to submit

Apply where the installation would break the 200 mm limit, rise above the ridge, sit on a flat roof with tilt framing, exceed the stand-alone limits, or fall within an Article 4 area. Apply separately for listed building consent where the building is listed.

What to submit for a householder application:

• Existing and proposed roof plans and elevations showing the array position and extent.
• A section through the roof at the array, dimensioned to show the projection from the roof plane.
• The panel and mounting system data sheet, with the frame depth.
• Photographs of the roof from the street and from any position where the array would be visible.
• A short note on the orientation assessed and the yield comparison, which addresses the appearance condition directly.
• A Planning Statement where the proposal is contentious or the property is in a sensitive location.

Fixings and projections on a house elevation raise closely related questions, covered in our note on flues, vents and stoves on a house elevation, and the general approach to measuring small projections is set out in our note on bay windows, canopies and small projections.

PlanScope can draft the supporting statements for an installation of this kind in minutes. Reports should be reviewed before submission, and we do not guarantee planning approval. To check what your address is likely to need, enter your postcode on PlanScope.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. A Lawful Development Certificate is the only formal way to confirm that works are lawful.