There are several reasons why a homeowner may consider using a high powered pressure washer on a roof:
- To brighten up/clean the roof
- To remove moss that has built up on the tiles
- In preparation for a roof coating/sealant
Why You Should NEVER use a Pressure Washer on ANY Roof Tiles
The most common roof tiles in the United Kingdom are made from concrete and have a sandy/granular finish on the exposed side of the tile. This part of the tile is designed to gradually wear off until the tile needs to be replaced, usually after 80-100 years of normal weathering.
Using a high powered pressure washer will strip the surface of the tile and shorten it’s life expectancy.
This damage is a fact.
There is also a high risk of flooding to the loft space or at the least to the felt and timbers hidden away in the roof. While a typical roof is designed to withstand the elements, it isn’t designed to cope with water being ejected from a nozzle at such high speeds.
The water may penetrate past the overlaps in the tiles and enter the roof. If the underfelt is torn (as often happens with older roofs) then the water may puddle on top of the ceiling.
That is exactly what happened to a property that was featured on BBC 1′s Rogue Traders programme.
The roofing company didn’t check the condition of the felt before they blasted the roof tiles with a pressure washer. The water not only penetrated past the tiles but leaked through the old felt and puddled on the loft insulation.
Luckily this insulation prevented the water from getting onto the ceiling where it could have dripped into the house and onto electrics such as light fittings.
Read about this story on the BBC website (opens in new window)
How many homeowners actually go into their loft and check the condition of the felt, timbers and insulation after having the tiles pressure washed?
Felt may fail and roof timbers will rot if subjected to water.
Using a pressure washer on an old roof is not a good idea at all! Even if things seem to look okay at first sight, there may be hidden water damage.
You may also find your neighbours are not too impressed when they see the moss and dirt from your roof being blasted onto the their property. Some pressure washers can blow moss and sludge several metres off the roof.
If you are a homeowner looking to remove roof moss or otherwise brighten up your roof then there is another option. You will be pleased to know it doesn’t involve any pressure washing and there is no flood risk at all.
Read more on how to remove roof moss without pressure washing.
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