Can cleaning a roof cause leaks?

How can cleaning a roof cause a leak?

Roof tiles and slates overlap so that rain runs down the roof and off it. A clean causes leaks when it works against that:

• A jet aimed up the roof. A pressure washer pointed up the slope can drive water under the overlaps between tiles, into the underlay and the timber battens. Roofing guidance warns that pressure washing can force water into the roof space, especially when it’s sprayed upwards from the ground.
• Cracked tiles underfoot. Walking on a roof can crack tiles and slates. A hairline crack may not show at first, then open up after a frost and let water in months later.
• Moss left in the gutters. Moss that comes off the roof often lands in the gutters. If it’s left there, they block and overflow, and water can back up onto the roof.

All three come down to how the roof is cleaned. See whether pressure washing damages a roof for the other harm a jet wash can do.

Can a soft wash cause a leak?

A soft wash works differently. The cleaning solution is applied at low pressure, left to work on the moss, algae and lichen, and then rinsed off gently, and a biocide kills the growth at the root. Because it isn’t driving water up the roof at force, there’s little risk of pushing water under the tiles. Roofing guidance says any washing should run down the roof, from the ridge towards the gutter, never upwards.

At Washmates, we match the method to your roof, and never use a high-pressure jet wash. Every roof is then treated with a biocide, and we don’t walk on fragile tiles: the work is done from roof ladders, scaffold towers or a cherry picker. Every roof clean includes clearing the gutters, and every crew is fully insured.

Can a roof clean uncover problems that were already there?

Yes. Heavy moss can hide cracked tiles, damaged flashing and other problems underneath it. On an older roof, the problems a clean can uncover include:

• Cracked, slipped or missing tiles and slates. Missing or shifted tiles let water in and can cause damp inside the home.
• Loose ridge tiles or missing mortar along the ridge.
• Damaged flashing, the seal around chimneys and where the roof meets a wall.

The clean didn’t cause them, but it can be the first time they’re seen. If you can already see cracked or slipped tiles, or there’s damp in the loft, get a roofer to look at the roof before it’s cleaned. Our guide to whether moss damages roof tiles explains what moss itself does, and whether roof cleaning is worth it covers when to call a roofer first.

What are the signs of a roof leak?

The signs are the same whatever caused the leak. Look for:

• A water stain or damp patch on an upstairs ceiling, especially one that appears when it rains.
• Water stains or wet patches in the loft.
• Daylight showing through the roof from inside the loft.
• A musty smell or mould upstairs.
• Outside, damp stains on the walls or water spilling over the gutters.

Before blaming the roof, check the loft for a leaking water tank or pipe, which can leave the same stain on a ceiling. After a roof clean, a look in the loft with a torch after the next heavy rain tells you whether everything is dry.

What should you do if your roof leaks after cleaning?

1. Limit the damage. Put a bucket under any drip and move belongings out of the way. If water is near a light fitting or socket, switch that circuit off at the fuse box.
2. Take photos of the ceiling, the loft and the roof from the ground.
3. Tell the company that cleaned the roof straight away. A professional roof cleaner should carry public liability insurance, which is there to cover damage caused while the work is done.
4. Get a roofer to find the cause. A roofer can find where the water is getting in and make a temporary repair.
5. Speak to your home insurer before arranging repairs. They may ask for photos and have their own repairers. Home insurance typically doesn’t cover wear and tear or gradual deterioration, so what caused the leak matters.

Don’t climb onto the roof to look for the problem yourself. Wet tiles are slippery, and falls from height are the most common cause of fatal accidents at work in Great Britain.

How do you choose a roof cleaner who won’t cause a leak?

Ask before you book:

• How will the roof be cleaned? Look for hand scraping, steam at low or very low pressure, a low-pressure soft wash, or a dry air wash with compressed air. Avoid a high-pressure jet wash.
• Will anyone walk on the tiles? A professional works from properly supported roof ladders, crawling boards, scaffold towers or a cherry picker, not by walking on the tiles.
• What happens to the gutters? The moss that comes off the roof often ends up in them, so they should be cleared.
• Are you insured? Public liability insurance is there to cover damage caused while the work is done.

Tell the cleaner about any cracked tiles or damp in the loft before they start, and what your roof is made of if you know; see whether clay, concrete and slate roofs can be cleaned. You can also see typical roof cleaning prices by type of house. If your roof is sound and the moss is building up, tell us about your roof and we’ll send you a fixed price, usually without a site visit.