Solar panels on a flat roof: what you need to know

A flat roof does raise its own questions: planning limits, how the panels are held down, wind, and keeping the roof watertight.

In England, rooftop solar on a house is usually “permitted development”, so no planning application is needed within the limits. Flat roofs got their own limit on 21 December 2023; the government said the change meant homes with flat roofs could fit panels without planning permission. For a house, the main points are:

• Height. The highest part of the panels and frames can’t be more than 0.6 metres above the highest part of the roof, not counting any chimney.
• Protected areas. In a conservation area, national park, the Broads, an Area of Outstanding Natural Beauty or a World Heritage Site, you must apply to the council before starting, so it can decide whether to approve the appearance.
• Listed buildings and scheduled monuments aren’t covered, so speak to the council.
• Appearance. Panels should be placed, as far as practicable, to minimise their effect on the building and the area, and removed when no longer needed.

The rules are updated from time to time, so check the current position on the Planning Portal or with your council before you commit. Leaseholders may need the freeholder’s permission too. See do you need planning permission for solar panels? for England, Wales and Scotland.

Wales and Scotland have their own rules. The Welsh Government’s guidance says panels on a flat roof can’t be within 1 metre of the roof’s outside edge or stand more than 1 metre above the roof. The Scottish Government’s 2024 householder guidance says no part may stick out more than 1 metre from the roof surface, with separate rules for listed buildings, conservation areas and World Heritage Sites.

The Planning Portal says building regulations normally apply, and the roof’s ability to carry the load has to be checked. MCS says a system must not harm the building’s weather tightness or structure for its whole life. Before panels go on:

• Check the roof’s age and condition. If the covering is near the end of its life, re-cover it first. Otherwise the panels have to come off again when it’s replaced. If panels are already on the roof, see solar panel removal and refit.
• Protect the membrane. Under ballasted frames, MCS requires a protection or slip layer that is compatible with the waterproofing. Mounting manufacturers use protection mats so metal parts can’t scratch the roof surface.
• Check any cover on the roof. If your roof covering is still within the roofer’s or manufacturer’s cover, MCS says to ask them whether fitting panels would affect it.
• Keep water moving. The layout shouldn’t change how rainwater runs off the roof or block outlets.

Panels tilted up to the south cast a shadow behind them, especially when the sun is low in winter. The rows need gaps between them, which limits how many fit.

East–west frames lean pairs of panels back to back in low rows that sit close together. One mounting manufacturer says its east–west system maximises roof space and module density, and the trade press notes that more panels can mean more generation overall, even though each produces less. Lower frames also catch less wind.

Watch for other shade too: parapet walls, chimneys, roof lights and neighbouring buildings.

Flat roofs look safe to walk on. They’re not. The Health and Safety Executive says the main causes of death and injury in roof work are falls from roof edges and through fragile roofs and roof lights. It says all roofs should be treated as fragile until a competent person confirms otherwise, and flat roof edges need proper edge protection.

Please don’t go up yourself to check or clean the panels, and don’t touch the cables: panels produce electricity whenever there’s daylight. Our engineers use the right access equipment. See solar panel maintenance.

Our own engineers fit both ballasted and fixed systems on flat roofs, and we carry out the structural assessment ourselves. If the roof needs re-covering first, we work with a roofer so it’s done before the panels go on. We survey flat roofs across England, Wales and southern Scotland and give you a clear written quote. See solar panel installations and how many solar panels do I need?

Sources: The General Permitted Development Order (England), Part 14 Class A; Welsh and Scottish Government planning guidance; MCS MIS 3002; Energy Saving Trust; HSE.