Installing Solar Panels on a Flat Roof

Flat roofs and solar panels are a natural combination. Unlike pitched roof installations, flat roof solar panels can be mounted on frames tilted to the optimal angle for maximum energy generation, regardless of which direction the roof faces.

Mounting Systems for Flat Roofs

Flat roof solar systems typically use ballasted frames — weighted frames that sit on the roof surface without penetrating the waterproofing membrane. This is the preferred approach as it avoids any risk of puncturing the roof. Alternatively, penetrating fixings can be used with proper waterproof detailing.

Roofing Considerations

Before installing solar on a flat roof, the roof condition must be assessed. Solar panel systems have a lifespan of 25+ years — if your roof membrane is approaching the end of its life, replace the roof first. It will be far more disruptive and expensive to remove and refit panels later.

Structural Load

Solar panels and frames add load to the roof structure. A structural engineer should confirm the building can handle the additional weight. For domestic extensions, this is usually straightforward. For older commercial buildings it requires more detailed assessment.

Planning Permission

Solar panels are generally permitted development on domestic properties, including on flat roofs, as long as they don't project more than 200mm above the roof plane. Listed buildings and conservation areas are subject to additional restrictions.

Getting the Sequence Right

Always sort the roofing first, then the solar installation. Coordinate with both your roofer and solar installer before work starts so that fixings, cable routes, and any penetrations are properly detailed and waterproofed.