There’s something deeply satisfying about jet washing. Anyone who’s ever cleaned their deck or patio with one will know – the way the water cuts through years of grime, moss, and algae like a hot knife through butter. That satisfying, perfectly clean streak… It’d almost be therapeutic if it weren’t so noisy and dirty!

But when it comes to cleaning roof tiles (especially delicate heritage slate tiling or traditional Kent peg tiling), breaking out your jet washer could be one of the most expensive mistakes you ever make.

Can you jet wash roof tiles? The short answer is no.

It might seem like a good idea for getting your roof tiles cleaned up, but it can be unbelievably destructive. Yes, roofing is designed to be waterproof – but it’s not designed to subjected to pressurised jets of water travelling at speeds of up to 440 mph!

Pressure washing can cause irreversible damage to roof tiles, stripping away outer layers of material. Pressurised jets from pressure washers can exceed 4000 PSI, forcing water beneath tiles, and even cracking or dislodging them entirely.

What seems like a quick fix for a dirty roof could end up costing thousands in repairs, not to mention all the water leaking into your loft space.

Jet washing roof tiles is a bad idea

Pressure washers can crack and break tiles. Slate and Kent peg tiling is durable, but not indestructible. High pressure water jets can easily chip or fracture slate tiles, especially older, weathered ones.

Kent peg tiles, which rely on careful placement and lapping, can be dislodged quite easily too, and being made of porous clay, can become saturated to the point of leaking into the loft space. The jet can force water under tiles as well, leading to leaks, soaking the battens and felt underneath. This can lead to rotting roof timbers, mould growth in the loft, and water damage. Even if the tiles look cleaner, the hidden damage could silently worsen over time.

At higher pressures, the water jet can crack a tile, or even cut through it. 

You might think you can run softer pressures and get away with it. But while your heritage roofing tiles might not show immediate signs of failure, their lifespan can be drastically reduced by having water forced into them.

The worst part? Jet washing doesn’t even solve the root problem. Moss and algae grow back, often faster after pressure washing – because the protective patina the roof had built up is gone. You’ll likely be back to square one within a year.

So, if jet washing is off the table, how should you clean your roof?

Safe alternatives to jet washing

Sometimes – in fact, most of the time – there’s no real need to clean your roof tiles. Moss and lichen growth is normal and expected, and it only becomes a problem when it’s excessive. When mosses and lichens build up to the point where they block the flow of rainwater and start getting washed into gutters, then it’s time to act.

Moss and lichen growth is usually strongest on shady parts of a roof – under trees, and in areas where birds stop to perch (as their poo acts as fertiliser, speeding up growth).

Leaves and gunk are probably a bigger concern, as they can get into gutters – and that can be concern.

Read more: Guttering and Historic Roofing – Essential for Roof Health

Clearing your roof of leaves and moss can simply be done by hand – or with a brush.You can absolutely use a low pressure spray to wash the roof off, combined with treatment solutions to kill moss, algae, and lichen – without damaging tiles.

But it’s not without risk, and being up high on a roof isn’t for everyone.

If you have slate tiling or Kent peg tiling, a heritage roofer could quickly clean and treat your roof with the safest cleaning method. They’ll also check for loose or damaged tiles, blocked gutters, and any other causes for concern.

When to call a heritage roofing expert

DIY cleaning might seem like a cheap and easy way to clean your roof. But the risks outweigh the savings. Get an expert assessment, and spot hidden issues before they worsen – with safe and effective cleaning for your slate and Kent peg tiles.

And remember: don’t ever be tempted to jet wash your roof tiles. The long-term consequences (cracked tiles, water damage, and diminished roofing lifespan) simply aren’t worth it. For slate and Kent peg tiling, gentle cleaning and professional maintenance are the only safe ways to keep your roof watertight, structurally sound, and looking beautiful for years to come.

Slate and Kent Peg Tiling Since 1984

Want to expand the lifespan of your heritage property? Get the advice and help you need, from our experienced team of heritage roofing experts. We specialise in traditional slate tiling and Kent peg tiling, including cleaning, care, and maintenance. For a quote, contact us at [email protected].