Figuring out how to clean cedar shake shingles is usually a weekend project that most homeowners dread until they see that first patch of green moss taking over their roof. It's one of those tasks that feels a bit intimidating because wood is a "living" material—it reacts to the sun, the rain, and definitely to the chemicals you throw at it. If you're staring at a roof that looks more like a forest floor than a high-end architectural feature, don't panic. You can get that silvery-gray or rich cedar look back without spending a fortune on a professional crew.
The trick is knowing that cedar is a bit of a diva. You can't just treat it like a concrete driveway or a vinyl fence. If you go in too hard, you'll end up with fuzzy, damaged wood that rots twice as fast. Here is the lowdown on how to do it right, safely, and effectively.
Why you should skip the pressure washer
If there's one thing you take away from this, let it be this: put the pressure washer away. I know it's tempting. It's fast, it's satisfying, and it makes for great videos. But high-pressure water is the absolute enemy of cedar shingles.
Cedar is naturally fibrous. When you hit it with a high-PSI stream of water, you aren't just blowing off the dirt; you're literally shredding the wood fibers. You'll end up with a "furry" texture on your shingles that looks terrible once it dries. Even worse, that high pressure can force water up under the shingles, leading to leaks and mold in your attic that you won't notice until it's a massive problem.
Instead of blasting the grime away, you want to use a gentle chemical approach. Let the cleaning solution do the heavy lifting, then just rinse it off with a standard garden hose.
What you'll need before getting started
You don't need a lot of specialized gear, but you do need the right stuff. Don't try to wing it with whatever is under your kitchen sink.
- A pump-up garden sprayer: This is how you'll apply your cleaning solution evenly.
- A sturdy ladder: Make sure it's rated for your weight and the height of your roof.
- Safety gear: Think non-slip shoes (crucial!), eye protection, and rubber gloves.
- A garden hose with a decent nozzle: No high-pressure tips needed.
- The cleaning solution: You can buy a commercial cedar cleaner or mix your own.
If your roof is particularly steep, please don't try to be a hero. It's better to hire someone with a harness than to end up in the ER because you slipped on a patch of wet algae.
Choosing the right cleaning solution
This is where the debate usually happens. Some people swear by bleach, while others think it's too harsh. Here's the reality of both options.
Oxygen Bleach (The Safer Bet)
Oxygen bleach (like OxiClean, but usually in a more concentrated powder form) is generally the best way to go for DIYers. It's non-toxic to your plants and won't kill the grass around your house. It works by breaking down the organic matter—the mold, mildew, and algae—without stripping the natural color out of the wood. It's a bit slower than the harsh stuff, but it's much more forgiving.
Chlorine Bleach (The Fast Option)
A lot of pros use a diluted chlorine bleach solution because it kills everything instantly. However, it can be really tough on your landscaping. If you go this route, you have to soak your plants in fresh water first and keep rinsing them so the runoff doesn't kill them. Bleach can also leave the wood looking a bit "blanched" or unnaturally white if you aren't careful.
Specialized Wood Cleaners
You can also find "Cedar Wash" products at most big-box stores. These are usually formulated with sodium percarbonate. They're specifically designed to lift the gray oxidation and kill the green stuff without hurting the integrity of the wood.
The step-by-step cleaning process
Once you've got your supplies, wait for a cloudy day. You don't want to do this in the middle of a 90-degree afternoon because the cleaning solution will dry out before it has a chance to work.
1. Prep the area
Move your patio furniture, cover any delicate plants with plastic sheeting, and make sure your gutters are clear. If your gutters are clogged, the cleaning solution and all that loosened gunk will just sit there and rot your fascia boards.
2. Mix your solution
Follow the instructions on the package. If you're using oxygen bleach powder, make sure it's fully dissolved in warm water before you pour it into your sprayer. If there are undissolved clumps, they'll clog your sprayer tip and drive you crazy.
3. Wet the shingles
Before you put the cleaner on, give the roof a quick spray with plain water. You want the shingles to be damp, but not dripping wet. This prevents the wood from soaking up the cleaner too deeply, which helps it focus on the surface-level mold and algae.
4. Apply the cleaner
Start from the bottom and work your way up. This might sound counterintuitive, but if you start at the top, the cleaner will run down and create "streaks" on the dry wood below. By starting at the bottom, you ensure an even coat. Let it sit for about 15 to 20 minutes. Don't let it dry out. If it starts to look dry, hit it with a light mist of water.
5. Scrub if necessary
For those really stubborn patches of thick moss, you might need a soft-bristle brush. Don't use a wire brush! Just a gentle scrub is enough to loosen the roots of the moss once the chemical has done its job.
6. Rinse thoroughly
Using your garden hose, rinse from the top down. This is the satisfying part. You'll see the brown and green water running off, revealing the clean wood underneath. Take your time here—you want to make sure every bit of the cleaner is gone.
Safety is the biggest factor
Roofs are dangerous. Wet roofs are even worse. Cedar shingles, when wet and covered in soap, are basically a slip-and-slide. If you can do the job from a ladder rather than walking on the roof, do that. If you must walk on the roof, wear shoes with incredible grip (some people even use specialized "roofing boots" with foam soles).
Always have a "spotter" on the ground to hold the ladder and keep an eye on things. If at any point you feel sketchy about the height or the pitch, just stop. No amount of curb appeal is worth a fall.
Dealing with moss and lichen
Moss isn't just an aesthetic problem; it's a structural one. Moss holds onto moisture like a sponge. When that moisture stays trapped against the cedar, it prevents the wood from drying out, which leads to rot.
If you have thick clumps of moss, you might need to do a "pre-treatment" where you scrape the big chunks off with a plastic putty knife before you even start the chemical cleaning. Just be gentle. You don't want to gouge the wood or snap a shingle.
Post-clean maintenance
Once your roof is clean and dry (wait at least 48 hours of dry weather), you might want to consider a preservative. There are oils and water repellents specifically made for cedar shakes. These products help keep the moisture out and usually contain UV inhibitors to stop the sun from turning the wood gray too quickly.
However, avoid "sealers" that create a hard film. Cedar needs to breathe. If you "plasticize" the surface with a heavy-duty sealer, you might trap moisture inside the wood, causing it to rot from the inside out. Stick to penetrating oils or breathable stains.
How often should you do this?
Generally, a good deep clean every 5 to 7 years is enough for most climates. If you live in a very rainy area or have a lot of overhanging trees, you might need to do it more often. A good rule of thumb is to keep the trees trimmed back at least three feet from the roof line. This allows for better airflow and helps the shingles dry out faster after a storm, which naturally prevents mold from growing in the first place.
Cleaning your own cedar roof is a big job, but it's one of those things that pays off immediately. Your house will look years younger, and you'll be extending the life of your roof by a decade or more. Just remember: stay off the pressure washer, stay safe on the ladder, and let the chemicals do the hard work for you.