Can you pressure wash your roof? And is it safe?

We have posed two questions for this blog because many people have asked us the first one, but few actually consider the second.
Many people assume that because the main purpose of a pressure washer is to blast away dirt, they can be used to clean a multitude of surfaces.
In actual fact, pressure washers, with a high-pressured nozzle, can do more damage than good if used on certain surfaces or for certain tasks.

So, what are they good for?

Entry level or mid-level pressure washers, up to a maximum of 120 bars, are good for cleaning dirty bikes, cars and giving your garden furniture a quick spruce up before the summer or after a particularly crazy garden party.

What about dirty paths, patio, walls and roofs?

If you want to tackle moss, lichen, algae and mould growth on surfaces, such as roofs, walls, patios and paths, a pressure washer might make them look cleaner, but all it’s really done is move it around the surface without killing the growth at the ‘root’.

Those unsightly microorganisms will simply grow back.

What’s more, since you’ve spread them around with a pressure washer, they’ll grow back in more places than before!

But what about roofs?

Roofs are one of the worst surfaces that you could possibly use a pressure washer on, especially tiled roofs.


Most roof tiles are designed and laid to overlap one another, creating a channel for rainwater to run off into the gutter. As rain doesn’t fall upwards, there is little to no risk of it penetrating past the overlapped tiles and flooding the roof cavity, unless the tiles are damaged.

When you use a pressure washer to clean your roof, the water is ejected at such high speeds that it can spray into the overlapping tiles and penetrate the roof space.

This can soak into the insulation in your roof, which will reduce its insulating quality as well as potentially causing it to travel to the bottom of the insulation, causing mould, which could turn into a serious health risk, and wood decay within the interior.

Flooding isn’t the only risk to using a pressure washer on a roof either.

Most concrete tiles, the most common type of tile in the UK, are designed to last 80-100 years of normal weathering before needing replacing, with the fines on the surface of the tile wearing away gradually over time.

When you use a pressure washer to clean your roof, you can remove the fines on their surface, decreasing their lifespan significantly.

Pressure washing can damage the construction of the roof, as well as the tiles.

Along with the tiles, pressure washing roofs can also cause considerable damage to the pointing on the roof, especially where there is considerable moss, lichen and other growth on them. Moss particularly will grow and force itself in cracks within the pointing, allowing water in. Once water gets in the cracks in the pointing, it can freeze in cold weather and expand those cracks even further, loosening the pointing considerably.

When you use a pressure washer to get rid of the moss on the surface of the roof, the huge amount of pressure that the water is ejected at can blast the loose pointing away, causing further damage to the roof and increasing the risk of flooding in the roof cavity.

So, pressure washers are no good for cleaning roofs. What should be used instead?

At SkyLine Softwash, we use a specialist treatment to kill the fungus, moss, mould and algae growing on the roof at the root after clearing away any particularly problematic areas gently by hand, if required. We then let the natural weather cycles wash away all the dead microorganisms over a period of 6-12 months.

Within a year, your roof is 100% moss free.

At Skyline Softwash:

  • We do not use high-pressure water jets on your roof.
  • We are fully trained to work at heights, if required
  • We provide a 5 year spot-free warranty on our roof cleaning services.
  • We are fully insured.

We also work from the ground up, doing as much of the work as we can from ground level, to keep costs down by reducing the need for access equipment.

If you’d like to have your roof cleaned safely, leaving it cleaner for longer in the process, get in touch with the SkyLine Softwash team on 01452 301342.