Should you jet wash your roof?

No — and here's why. Pressure washing has become a popular "quick fix" for a mossy or dirty-looking roof, and we understand the appeal — a jet washer makes a roof look clean again in an afternoon. But we won't do it, and we'd advise against hiring anyone who offers to. Here's the actual reasoning, not just a blanket "don't."

It strips the protective surface off your tiles

Concrete and clay tiles have a granular or sanded coating that protects the material underneath and helps water run off properly. A pressure washer doesn't just remove moss — it blasts that coating away too. Once it's gone, it doesn't come back, and the tile underneath wears faster from then on. You're trading a cosmetic fix now for a shorter roof lifespan later.

It forces water where it isn't supposed to go

Roof tiles are designed to shed water running down and off them — not to withstand a high-pressure jet aimed directly at and under their edges. That force can drive water up and underneath tiles, into the felt and battens below, which is exactly the kind of hidden dampness that turns into a leak or timber rot months later, long after the roof looked "clean."

It can crack tiles that are already ageing

A tile that's fine under normal weather can't necessarily take a concentrated blast of pressurised water. On an older roof especially, this is a common way to turn "a bit mossy" into "several tiles need replacing."

It can dislodge pointing and ridge tiles

The mortar bedding ridge tiles and verges in place isn't built to withstand direct pressure washing either — it's a common cause of loosened ridge tiles that then need re-bedding.

It often doesn't even solve the actual problem

Moss and green discolouration are usually biological growth, not just surface dirt — blasting it off removes what's visible today, but the spores and roots left behind mean it frequently grows back faster and thicker than before, since you've also just stripped away the smoother protective surface that made it harder to take hold in the first place.

What we'd do instead

Soft washing with an appropriate biocide treatment — kills moss and algae at the root without any pressure, protecting the tile surface rather than stripping it.

Manual removal for heavy moss build-up — carefully scraping and brushing off by hand, working with the tile rather than against it.

Keeping gutters clear — most moss growth is made worse by damp, blocked gutters holding water against the roofline; sorting that out stops it coming back nearly as fast.

A roof that looks slightly mossy from the ground is rarely an emergency. A roof that's had its protective surface pressure-washed away is a problem you've paid to create. If you're not sure what your roof actually needs, that's exactly what a proper inspection is for, rather than reaching for the jet washer first.