Washing a roof
Can you pressure wash a roof without damaging it?
A powerful jet shortens a tile's life, while hand brushing and a soft wash do not. Below: what a jet does, gentler methods, and what to ask a cleaner.
The short answer
No, a high-powered pressure wash is not a safe way to clean a roof. Marley, the tile maker, says the use of high powered jet washes is not recommended on slate or tile, because it can damage the surface and reduce its expected life considerably. A roof can still be cleaned well: growth is lifted by hand, then treated with a low-pressure spray. That is how we work, and it is the method to ask any firm you are comparing about.
5 min read ยท Part of Roof cleaning
What a jet does to the surface
A tile's outer face is part of how it sheds water and holds its colour. A narrow, fast jet strips growth quickly, but it can strip the face of the tile along with it, which is the harm Marley points to when it says jet washing is not recommended for slate or tile.
The loss is gradual and easy to miss. A roof cleaned that way can look bright for a season while the tiles underneath carry the cost, and the maker's own words are that their expected life is reduced considerably. Nobody can reverse that afterwards, and no repair puts the face back on a tile.
Hand work is slower. The same roof takes longer, and the quote reflects the hours, but each tile is in the same condition afterwards as before, minus the growth. That trade is why we work the slower way, and why a cleaning price built on speed deserves a question.
Where a tile is already cracked or flaking, a jet will simply make it worse. It is one more reason the look comes before the method.
Three methods set side by side
Three approaches turn up in cleaning quotes. This is how each sits against the tile, and where it falls in the order of work on our roofs.
| Method | Effect on the tile | Our view |
|---|---|---|
| High-powered jet | Can damage the surface | Left off the roof |
| Hand brushing | Gentle, slower | The first step |
| Low-pressure spray with biocide | Gentle on the face | The second step |
A very low price can mean the first method was used. Our guide to roof cleaning cost explains what to look for in a written quote, so two firms can be compared properly. Where quotes differ widely, ask about the method before you ask about the size of the roof, the number of visits or the scaffold, because the method is the part that cannot be undone afterwards.
The table is also a guide to cost. Hand work takes hours, and a low-pressure spray takes planning, so the honest price for a gentle clean is higher than for a quick blast. That difference buys a roof that comes through the clean unharmed, with every tile checked by eye, and it is a difference you can ask any firm to explain in plain terms before you agree.
Questions to put to a cleaner
Before you accept a price, put these to whoever is quoting. The answers tell you far more than the number does.
- What kind of washing will the tiles get: a jet, or a low-pressure spray?
- Is the thick growth lifted by hand first?
- Which biocide goes on, and what does its label say about weather?
- Who clears the gutters, and where does the debris go afterwards?
- How will cracked or slipped tiles be reported to you?
A cleaner who answers these plainly is working the way tile makers advise. One who goes vague on the first question is worth a second question, and perhaps another quote. We are glad to be asked the same list, and to talk it through on the phone or by WhatsApp before anyone books a survey, so you know what the day will involve.
Ask for the answers in writing if you can. A written quote that names the method, the product and the gutter clearing is easy to compare with another, and it protects both sides if there is a question later. If a firm will only talk about the price and not the method, treat that as an answer in itself.
When washing is the wrong job
Some roofs need a repair before anything touches them with water. Cracked tiles, slipped courses and loose ridge bedding let rain in whatever the cleaning method, and a clean on top of them only makes the fault easier to see later, when a ceiling stains.
On the survey we look at the roof before settling on a method. Sometimes the right order is a repair first and a clean afterwards, and sometimes the roof is clear enough to leave alone for now. Our main page on roof cleaning and moss removal shows how the work is taken in order.
Where the roof is sound, the clean is simple: hand work, a gentle spray, the gutters cleared and the site left tidy. You receive a single written total once we have surveyed the roof, and nothing is added without your agreement. If solar panels sit on the roof, our answer on cleaning a roof with solar panels covers that case.
If you cannot tell whether your roof is ready for a clean, photos from the ground are a good first step, and a ladder inspection will show the rest.
More questions
Is a soft wash enough to remove moss properly?
Yes, once the thick growth has been lifted by hand. The soft wash with a biocide deals with what is left on the surface, so the roof ends up clean without a jet touching the tile. A power wash can damage the tile and is quicker; the soft wash takes longer, which is why we price each roof after a survey.
Can I wash my own roof from a ladder with a garden hose?
We would advise against it. A wet roof is slippery, a ladder resting on a gutter can crack it, and a hose does little to growth that grips the tile. Send us photos instead, and tell you what the roof needs, and how it could be reached safely.
Tell us what's wrong with the roof.
You'll get one written total price.