How To Pressure Wash A Roof (Roof Cleaning Guide)

In many ways, the roof is the most important part of your property. A well-maintained roof protects your property from the worst of the weather preventing integral damage from high winds, rain and snow. How do you keep your roof in good condition?

According to many experts, moss growth on roofs can cause problems to the cement used to bond ridge tiles and apex tiles. Moss, along with dirt and algae build-up, can also cause the attic to overheat, by not allowing hot air to pass through the roofing material. This can lead to an uncomfortable living space and higher energy bills due to air conditioning.

The other problem with allowing moss to build up on the roof is in hot weather, the moss dries out, it then falls into the gutter causing a trap for any dirt and debris caught up in the wind. This, in turn, builds up and can block the gutter, causing rainwater to overflow and potentially damage the walls of your home.

How To Pressure Wash A Roof

It is important before we start getting into this, that not all roofs are suitable for pressure washing. Check first that your roof is constructed from materials that can be pressure washed safely. Then you’ll need the following items:

• A ladder – You’re going to have to get onto the roof, which means climbing a ladder to safely get up there.
• Plywood – Place the plywood on the roof so your weight is evenly distributed and doesn’t cause any damage to the roof tiles.
• A pressure washer – With no more than 1,200 PSi and the correct attachment.
• A detergent specially formulated to remove moss from roofs
• Replacement tiles – So any damaged tiles can be replaced while you’re already up there.
• Sealant – This is only necessary on certain types of roofing tiles, check before you start.

A Step By Step Guide To Pressure Washing The Roof

Always be mindful of where you are and what you’re doing, you are climbing a ladder up to the roof, and then walking on the roof. There is the possibility of losing your balance and falling either, off the roof or through the roof. Neither of which will do you much good, apart from the injury and pain, you might have to replace the roof! 

The following steps are the most efficient and effective way of cleaning a roof using a pressure washer.

1. Using the white nozzle on your pressure washer, soak the roof with water. Start from the ridge tile and work downwards.
2. Switch to the green nozzle to really cut through any dirt, moss or algae.
3. If this doesn’t clear the moss, use detergent with the black nozzle on your pressure washer. 
4. Rinse off using the white nozzle, be sure to remove all traces of detergents from the roof and from the walls. Starting at the ridge, work downwards.
5.  Once the roof is dry enough to tread on safely, replace any loose or damaged tiles.
6. If necessary, apply sealant.

Never under any circumstances use any other nozzles than mentioned above. The black, green and white nozzles are designed for low power operations, where there is a risk of damage from high-power water spray.

Pressure Washing Metal Roofs

If you want to clean a metal roof, you should find it’s an easier task than a tiled roof. Because metal roofs tend to be flatter and have less of a pitch, making them easier to walk on. The same principles apply, however, always use the lower-powered nozzles and work from the top, down.

If you have used any detergent on the metal roof, be sure to rinse off thoroughly to prevent corrosion. Once the roof is dry apply any suitable sealant. 

Pressure Washer Roof Cleaning Accessories

Many pressure washer companies make accessories specifically for cleaning roofs. These are designed to make roof cleaning with a pressure washer easier and include:

• Telescopic power poles – As the name implies, these poles can extend up to 43 feet (depending on model) Allowing safe roof cleaning, in many cases without having to climb onto the roof.
• Pole head brush attachment – Giving you the ability to brush the roof as you apply water.
• Gutter cleaning attachment – Attach this to the telescopic pole for easy cleaning those awkward gutters.
• Roof cleaner – Designed much like the smaller surface cleaners, the roof cleaner is attached to the power washer pressure hose and is lowered from the ridge over the roof.
• Roof cleaning detergents – These are roof specific detergents formulated to deal with problems like moss and algae growth. They leave a preventative residue that inhibits future growth.
• Full face masks – Made to protect the user from any spray or spillage of chemical cleaners. Or dirt and debris injury to the face and eyes.
• Industrial gloves – To protect the hands from any harmful chemicals or water damage, but allowing enough grip to be safe.

Is It Safe To Pressure Wash Your Roof?

This is one of the most contested questions within the roofing industry. Many roofers claim (and in many cases correctly) that pressure washing damages roofs. They say “if too much pressure is applied, slates can be split, damaged and in some cases torn from the roof”. Roofing slates are held onto the roof by a single nail, which under normal conditions is strong enough to hold the slate in place for many years.

Pressure washing is by no means normal conditions, the power from a pressure washer can be way too powerful to maintain the integrity of the roof. And it’s not just slates, many roofing tiles are made from concrete, and have a glazed finish to protect them from the weather. This glazing wears down over the years, and then the roof needs to be replaced.

Pressure washing can reduce the lifespan of these concrete tiles considerably. This can invalidate any guarantee your roofing contractor may have given you. That’s why it’s important to only use the white, green or black nozzle on your roof and only then if you are sure the roofing material is able to withstand the pressure.

Frequently Asked Questions