Solar panels on flat roofs

The roof check before panels go on

Before any solar install on a flat roof, three things need verifying:

• Membrane condition. The roof should have at least 15 years of life left in it. There's no point putting a 25-year solar array on a roof that needs replacement in three years — you'd have to take it down to do the re-roof, at significant cost.
• Structural loading. Ballasted arrays add around 25kg/m² distributed load to the roof. Most domestic flat roof decks built since 1965 can handle that, but the calculation should be done — particularly on older garage roofs and dormer extensions.
• Wind uplift design. The ballast weights vary depending on the local wind exposure (Newcastle being relatively exposed compared to inland), edge zone vs central zone of the roof, and array size. A reputable PV installer will design this properly.

For a small surcharge we'll provide your PV installer with a written roof condition report and a confirmed remaining lifespan estimate. Most reputable PV installers ask for this anyway before warrantying their work.

If your roof's not ready

If we look at your roof and it's nearing end of life, the right answer is to re-roof before the panels go on. We'll quote both jobs — the re-roof and any membrane prep for the PV install — separately so you can see the full picture. Typically the additional cost of doing the re-roof first is far less than the cost of dismantling and reinstating a panel array later.

For an EPDM re-roof on a typical 30m² flat roof with a planned solar install on top, we'd usually upgrade the membrane to a thicker grade (1.5mm rather than 1.2mm) and use a higher-grade adhesive system. Extra cost is small; difference in working life is substantial. The roof will then comfortably last 30+ years under the panels.

Who we work with

We've worked alongside most of the established North East PV installers and have good relationships with several. If you've already chosen a PV installer, we'll happily liaise with them directly. If you haven't, we can recommend a few who understand flat roofs and design ballasted systems properly.

What we won't do is install panels on a roof against the membrane manufacturer's specification just because the PV installer "always does it that way." If the PV installer insists on penetrating mounts on an EPDM roof, we'll politely decline the work — the roof warranty is what you'll be relying on in 15 years' time, not a verbal assurance.

Maintenance after install

The panels themselves are basically maintenance-free. The roof beneath them needs the same care any flat roof needs — keep outlets clear, wash off moss every few years, inspect annually. The complication is that the panels make the membrane harder to inspect. We recommend a 5-yearly roof inspection on PV-equipped flat roofs, partial-strip if needed to look beneath the array. We'll do this for a small flat fee.