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Should You Pressure Wash Your Roof? Here’s Everything You Need to Know

When’s the last time you really looked at your home’s exterior? That’s an often-forgotten element of home maintenance tasks. If your siding is a light color, you’ve probably paid more attention than most people to the buildup of algae and dirt on your walls. But what about your roof? Roofing, too, can become unsightly. 

Rain does most of the heavy lifting when it comes to keeping your home’s exterior clean, but roofs still can accumulate grime. Once you notice, you don’t stop noticing algae stains or dirt. And if you don’t see it, your neighbors probably do. Keeping your roof clean is good for aesthetics as well as performance. 

It’s tempting to turn to roof pressure washing as an option to handle buildup (after all, it’s super satisfying to clean your sidewalk this way!), but before you turn on the hose, read on to ensure you don’t do any damage to your home. 

How do you know if your roof needs cleaning?

Step back as far as you can from your roof to look at the big picture, ideally from the street or from your neighbor’s yard. This will help you to see if you have any major visible streaks or marks. Some of this depends on your asphalt roof shingles colors: It’s hard to tell if your roof is dirty when the shingles are already dark, but if you have a lighter roof, staining should be relatively easy to spot.

For a closer look, get on a ladder and examine the roof from the top. Getting up close will help you to see exactly what’s going on with your asphalt shingles- algae, moss, and dirt are the most common culprits. Think about your roof’s performance too. An accumulation of lichen or moss doesn’t seem like it’s a big deal until it grows out of control. Too much moss can cause your shingles to curl, which is bad news for your whole roof.

If your roof is already damaged, cleaning won’t save it. If you’re seeing a lot of damage on your roof in addition to dirt and algae, it might be time to consider a roof replacement.

Can you pressure wash a roof and does it cause damage?

Short answer: Damage is a strong possibility.

Pressure washing roof shingles sends a heavy stream of water onto a concentrated area, which is a recipe for disaster. Most roofs are meant to handle spread out rainfall (even heavy rains), but all that water isn’t hitting the same small place for an extended period of time. Sending a pressured stream of water onto an asphalt or slate roof is a recipe for disaster. Water can get up under your shingles or break apart slate. It can send shingle debris into your gutters, which could clog the trough and cause additional damage.

Is it safe to pressure wash your roof?

Pressure washing isn’t typically recommended for cleaning roofs. Pressure washers are extremely powerful tools that can not only damage your roof by causing cracks and holes in your asphalt roofing shingles but can also introduce water damage to your home. Ultimately, you may end up needing a new roof installation if it results in damage.

Even metal roofs aren’t safe to pressure wash in the typical way; they too can become damaged in the process. Tile roofs are generally ok to pressure wash, but only if the tiles are in good condition. Otherwise, water can enter your roof deck through the cracked tiles and cause interior wreckage.

Some roof pressure washing companies offer a softer wash. This makes it more safe to pressure wash your roof than typical methods, but it’s still possible to harm your roof.

What is the best way to clean roof shingles?

If pressure washing roof shingles is too risky, what do professional roof cleaners use instead? One option for cleaning a roof is to use a bleach and water solution. Using a 1:1 ratio, spread the solution all around your roof. Let it sit for 20 minutes or so before rinsing it off (gently!) The bleach will kill harmful moss and algae.

It’s not a perfect solution, since depending on the severity of the grime problem you might need to repeat this process a few times. However, bleach works just as well outside as it does inside your home. This can be labor intensive. In addition, safety is a key consideration- wet roofs are slippery, so walking around on one involves putting yourself at risk for a dangerous fall. You could also look at adding zinc strips or copper as preventative measures if your algae problem is severe.

Hire a professional to clean your roof

The best way to clean your roof is to hire someone who knows what they’re doing. Experienced roofing professionals have seen it all and know how to wash your home’s exterior safely. Double check their license and insurance in the event that an accident occurs, and be sure to ask how their roof cleaning method avoids damaging your asphalt shingles.