Arizona is hard on shingled roofs. Between the UV exposure, monsoon dust, and algae streaks that show up even in the desert, your roof’s shingles are bound to get dirty. And you shouldn’t just leave them that way. Grime on your roof can trap moisture and break down your shingles faster than normal wear would. At Arrow Roofing, we know a thing or two about shingle roof cleaning, so we’re here to share what works and what to avoid.
The General Process for Cleaning Shingles
Whether you’re tackling this yourself or overseeing a contractor, you should know the general process for cleaning shingles. There is some variance depending on the type of shingles your home has (more on this later), but the basic steps are as follows.
Inspect First
Your first step is to check for damage, which typically presents as cracked, curling, or missing shingles. Cleaning a damaged roof can drive water under compromised shingles and make existing problems worse, so you must address repairs before anything else.
Choose the Right Solution
A 3:1 mixture of water and sodium hypochlorite (the active ingredient in bleach) is the industry-standard cleaning solution for most shingle roofs. You can add a small amount of trisodium phosphate (TSP) to deal with heavier buildup.
Apply the Solution
Apply the solution from the bottom of the roof section up. This prevents streaking, which happens when the cleaning solution runs down over dry, dirty areas faster than it can work. Let the solution dwell for 15 to 20 minutes before rinsing.
Rinse the Roof
Use a garden hose with a standard nozzle or a low-pressure rinse. Always rinse downward, following the direction of the shingles. This removes loosened debris, algae, and any remaining cleaning solution without forcing water underneath the shingles.
What You Must Avoid
Here are some common mistakes to steer clear of:
- using a power washer if you have asphalt or wooden shake shingles (It strips the protective granules and warps the shingles.)
- applying undiluted bleach directly to shingles (It’s too harsh and can dry out the asphalt binder.)
- scrubbing or brushing aggressively, which loosens granules the same way pressure washing does
- walking on wet shingles without proper footwear, which damages the granule surface and is a huge safety risk
- cleaning during peak heat hours in Arizona, which causes cleaning solutions to evaporate too quickly to be effective
- using products that contain citric acid or acetic acid, as they’re not effective against biofilms and can degrade asphalt through repeated use
Cleaning Considerations by Shingle Type
Not all shingles are the same, and the cleaning method that works on one type can cause problems on another. Here’s what you need to know for each major shingle type.
Asphalt Shingles
Asphalt is the most common shingle type, and it’s also the most sensitive to improper cleaning. As we mentioned, you should never, ever pressure wash this shingle type. Instead, use a low-pressure device (a pump garden sprayer works well) with a diluted bleach solution or a commercial algae remover rated for asphalt.
Tile Shingles (Clay and Concrete)
Clay and concrete tile are far more durable than asphalt when it comes to cleaning. They don’t have a granule layer to protect, so they’re less vulnerable to pressure washing. A low-pressure wash (under 1,200 PSI) is acceptable for tile roofs, though you still need to be careful around flashing and mortar joints. The same bleach-based solutions that work on asphalt work for clay or concrete tiles. You just have the ability to use a bit more pressure during the rinse.
The more important concern with tile roofs is walking on them. Clay tile in particular is brittle and can crack under direct foot pressure. If you’re cleaning your own tile roof, use foam-soled shoes and step on the lower third of each tile, which is where the structural support is.
Wood Shake Shingles
Wood shake requires the most careful cleaning approach. It’s porous, which means it absorbs cleaning solutions differently than asphalt or tile. Bleach-based solutions can dry out wood shake, causing it to become brittle.
For wood shake, use oxygen bleach (sodium percarbonate) instead of chlorine bleach. It’s gentler on the wood and still effective against algae and organic growth. Apply it with a low-pressure sprayer, let it dwell for 20 to 30 minutes, and rinse thoroughly.
Again, never use a pressure washer on wood shake. It can raise the wood grain and split the shake, creating pathways for moisture infiltration.
Metal Shingles
Metal shingles are highly durable and among the easiest to clean. They don’t support algae growth as readily as other materials, but they do accumulate grime that dulls their appearance.
For metal shingles, a mild detergent solution applied with a soft brush and rinsed with low-pressure water is all you need for routine cleaning. Avoid anything abrasive, and avoid bleach-based solutions on painted or coated metal panels, as bleach can degrade the coating finish. If you’re dealing with stubborn staining, use a product specifically formulated for metal roofing.
How Often Should You Clean Your Roof?
In Arizona, most homeowners should plan on cleaning their roofs every one to three years, depending on how fast grime settles in. But if your roof looks dirty, that’s your cue to clean it, even if it’s ahead of the schedule you planned.
When Cleaning Isn’t the Answer
Sometimes, a roof is past the point where cleaning addresses the problem. If your shingles are curling, cracking, losing granules in large patches, or showing signs of structural failure underneath the surface layer, cleaning won’t fix that. In fact, cleaning will probably make things worse. In this case, you’re dealing with a replacement situation, not a maintenance one.
The Right Call After a Thorough Cleaning
Now that you know what works for shingle roof cleaning and what to avoid, you’re in a better position to maintain your roof on a regular basis. But if your inspection turns up damage that cleaning can’t fix, or if you’re ready to replace your roof with a low-maintenance, perfectly installed upgrade, we’re here to help. Arrow Roofing is a residential roofing contractor serving the Prescott area, and we specialize in roof repair and full replacements. Give us a call, and we’ll take a look at what you’re working with.