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Can We Pressure Wash a Roof ?

can we pressure wash our roof

Photo by John Kinnander from Unsplash

If you own a pressure washer or have access to one you can borrow, you probably know it’s a great way to clean debris and contaminants off of surfaces. So, if you see lichen, moss, or algae growing on your roof shingles, you might be thinking about using a pressure washer to clean it. 

But can you pressure wash a roof? You could. However, it may be unsafe both for you and for some roofing materials, such as asphalt shingles. So, let’s explore how to clean a roof safely.

Downsides of Pressure Washing

There are several reasons pressure washers can cause damage to your roof and put you in danger too: 

  1. Pressure washers are made to rip objects off of hard surfaces, like cleaning gum off a sidewalk. But asphalt shingles are made of small parts, such as layers of gravel, which can be torn off by a jet of pressurized water. 
  2. Pressurized water can damage the glue that holds shingles together. It can also get under the shingles and allow moisture to seep into the lower layers of the roof, warping them or causing mold growth. 
  3. The sheer weight of a pressure washer could put you in danger as you pull it up a ladder or walk across your roof. It’s a risk. Plus, its weight could crack your shingles. 
  4. Water can make algae and mold slippery, which creates a falling hazard for anyone working there.

The pressure washer might be ineffective. It could knock loose the moss or other material you want to clean off but then throw it onto a different section of the roof. There’s no guarantee the roof will stay clean. 

Wash Your Roof Safely and Effectively

Is it safe to power wash a roof at all? Yes, you can do it, but it’s better to soft wash than pressure wash. Asphalt shingles are designed to channel rainwater, not pressurized jets of water, so try this method (using safety precautions): 

1. Divide the Roof into Sections

Start in an upper corner of the roof working your way across and down to the opposite corner where your ladder is. Make sure you are always standing in a dry area of the roof.

2. Use an Onboard Detergent Tank

This method is easier if you can get a washer that has a built-in detergent container. That way, you can apply detergent, flip a switch, and then spray the detergent off with plain water.

3. Apply Detergent

A cleaner made for moss, lichen, and/or algae loosens it from your shingles more effectively than water pressure can, so start by gently spraying a cleaner over the shingles. 

4. Softly Rinse Detergent

After applying detergent to one area of the roof, use your pressure washer on a low or medium setting to spray the detergent off, relying on the chemical power of the detergent to carry away the contaminants.

5. Aim Down the Roof

Always spray “downhill” and toward gutters. Keep your sprayer at least a foot away from shingles. If you were to spray toward the top of the roof, you could inject water under the shingles, causing damage to your roof.

It is your responsibility to always stand on a dry area of the roof, avoiding slippery surfaces. That is the main reason for working on the roof in sections. 

Can you pressure wash a roof? Really, if you want to avoid damaging your shingles, you won’t be using the full pressure wash treatment. You’ll depend on an appropriate detergent to clean your shingles. You can also use this more extensive 8-point roof cleaning advice from DMG Exteriors to become a DIY cleaning pro.

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