If you’ve spotted something growing on your shingles, whether it’s dark streaks, green fuzzy patches, or crusty discolouration that won’t budge, you’re not imagining it. And you’re not alone.
Moss, algae, and lichen are among the most common roof problems for homeowners in Barrie, Newmarket, and the surrounding area, thanks to our mix of heavy rainfall, cold winters, and plenty of shade from mature trees.
The good news? If caught early, all three are manageable. A proper roof cleaning can clear it off and buy your roof several more years of life.
The bad news? If left too long, moss, algae and lichen can go from a cosmetic issue to a structural one and no amount of cleaning will fix that.
This guide covers how to identify what’s growing on your roof, how to clean roof shingles safely, which products and methods actually work, and, just as importantly, the signs that tell you it’s time to pick up the phone instead of the garden sprayer.
They may look harmless but algae, moss and lichen share one thing in common: they hold moisture against your shingles. To make things more confusing, each causes damage in a different way. Knowing the difference helps you understand why treating them promptly matters.
Algae is the most common and the least immediately damaging of the three. It doesn’t lift your shingles or grow roots into them, but the dark streaks it leaves behind absorb heat, and over time it degrades the granules that protect your shingles from UV exposure. Left untreated, it quietly shortens the life of your roof.
Moss is more aggressive. Unlike most plants, moss gathers water through its leaves rather than its roots, which means it doesn’t need soil to survive. It grows directly into your shingles, acts like a sponge against the surface, and traps moisture that works its way under shingle edges and into the wood decking underneath. Thick moss can also get heavy enough to lift shingle edges, making them vulnerable to blowing off in a windstorm.
Moss spores spread easily too. What starts in one shaded corner can work its way across the whole roof within a season or two.
Lichen is the most stubborn of the three. It’s a combination of algae and fungus that bonds chemically to the shingle surface, almost like a living glue. It doesn’t respond quickly to treatment, can be impossible to remove without damaging the shingles beneath, and its presence often signals that growth has been establishing itself for years.
The takeaway is the same for all three: if you can see it, it’s already time to deal with it.
Not everything growing on your shingles is moss. Knowing what you’re dealing with before you treat it determines which method to use and what results to expect.
This is almost always algae (Gloeocapsa magma). It looks alarming but is the easiest of the three to treat.
A bleach and water solution will kill it, and you don’t need to physically remove anything afterward. It will fade and wash away on its own with subsequent rain. One treatment is usually enough.
This is moss. It often starts on north-facing sections or anywhere shaded by trees. If it’s raised or you can see it lifting shingle edges, it’s been there a while.
Moss needs to be killed first with bleach or a commercial cleaner, then loosened and removed, either by hand or with a leaf blower once it dries out. Severe growth may need more than one treatment.
Lichen is the most stubborn of the three. Bleach will kill it but won’t remove it immediately.
It typically takes several weeks and multiple rainfalls to fully clear after treatment. Don’t try to scrape it off as you’ll pull granules with it. If lichen is widespread, it’s worth having a professional assess whether the shingles beneath have been compromised.
Now that you know what you’re dealing with, here’s how to get rid of it. All three methods below work on algae, moss, and lichen but the approach and expectations are a little different for each, so we’ve noted where it matters.
The most effective method recommended by the Asphalt Roofing Manufacturers Association is a 50/50 mix of laundry-strength liquid chlorine bleach and water. It kills algae, moss, and lichen at the root and is safe for asphalt shingles when applied correctly.
Results vary depending on what you’re dealing with.
Algae is the fastest to clear. It dies quickly and washes away on its own with subsequent rains, often within a few weeks.
Moss takes longer. It will loosen over time and can be removed with a leaf blower once it dries out. Severe moss growth may need more than one treatment.
Lichen is the most patient of the three. Bleach will kill it, but it can take several weeks and multiple rainfalls before it fully clears. Don’t rush it by scraping or else you’ll pull granules off with it.
If you’d rather skip mixing bleach, professional-grade roof cleaners are a practical alternative. Most contain sodium hypochlorite as the active ingredient. This has a similar chemistry to bleach, but it is pre-measured, sometimes buffered, and easier to handle.
Look for products specifically labelled for asphalt shingles and that list algae, lichen and/or moss on the label. Some are formulated for one more than the other, so if you’re dealing with lichen, the hardest to shift, check that the product specifically covers it before you buy.
Apply the solution following the directions on the product. Usually this involves generously soaking the surface until it is thoroughly wet. Let it soak for 15–20 minutes, then rinse with low pressure.
Because formulations vary, one product may outperform another depending on what’s growing on your roof. If the first treatment doesn’t fully clear it, try a second before moving to something more aggressive.
Wear gloves and goggles regardless of the product. Sodium hypochlorite can irritate skin and eyes, and stronger formulations can harm nearby plants and soil if not rinsed away properly.
For thick, established moss that has been growing for years, you may need to physically remove the bulk of it before a chemical treatment can properly reach the shingles underneath.
This method does not apply to algae as algae has no physical mass to remove and is handled entirely by chemical treatment. This method is also not recommended for lichen, which bonds too tightly to the shingle surface to be safely lifted by hand.
For moss, once a chemical treatment has had time to work and the growth has loosened, gently lift it off the shingles by hand and place it in a bag for disposal. Work from a ladder where possible rather than walking across the roof surface as moss can be slippery and there is a chance that the roof decking has been compromised.
If moss is still too ingrained to lift by hand, do not resort to aggressive brushing or pressure washing. Both of these methods can damage your shingles. Pressure washing at high PSI blasts granules off the surface, forces water up under shingle edges, and can void manufacturer warranties.
If a job genuinely needs that kind of force, it’s a job for a professional who knows the right settings and angles for your specific roof.
Cleaning your roof once won’t keep it clean forever, especially in a climate with wet springs, heavy tree cover, and cold winters that slow drying. To help make a real difference between cleanings, regardless of whether you’re dealing with algae, moss, or lichen, follow these steps:
Shade is the single biggest contributor to moss growth. Cutting branches back improves sunlight exposure and airflow, and reduces the debris that traps moisture on your shingles.
Blocked gutters back water up along your roof edge, creating exactly the damp conditions that encourage growth of moss, algae and lichen. This is especially relevant for moss, which needs consistent moisture to take hold. Clear your gutters at minimum in spring and fall.
RELATED: Signs your gutters need repair
This is the most underused prevention method for all three.
When it rains, these metal strips release trace ions that wash down the roof surface and naturally inhibit algae, moss, and lichen from establishing. It’s a one-time installation that works passively for years.
This method of prevention is especially worth considering if you’ve had recurring lichen, which is the hardest to clear once it bonds to your shingles.
Cleaning too frequently or too aggressively strips the granular surface from your asphalt shingles, leaving them vulnerable to UV damage and accelerating wear. Every two to three years is generally appropriate, unless you have a heavy shade situation that encourages faster regrowth.
This is the part most roof cleaning guides leave out. If any of the following apply to your roof, a bleach treatment isn’t going to solve your problem and continuing to clean instead of repair or replace is costing you money.
Curling, cracking and lifting are all signs your roof needs attention. All three types of growth accelerate this, but moss and lichen are the biggest culprits. Moss forces moisture under shingle edges, while lichen bonds to and degrades the shingle surface itself. Once shingles are physically deformed, no amount of cleaning will reshape them. Curl or lift means moisture has already gotten underneath.
Run your hand through your gutters after rain. A small amount of granule loss is normal but handfuls of grit are not.
Algae accelerates granule degradation through heat absorption, while moss and lichen physically dislodge granules as they grow into the shingle surface. Heavy granule loss means your shingles are past their protective lifespan regardless of how clean the surface looks.
Where the granule coating has completely worn away, you’re looking at exposed asphalt and a countdown to leaks. This is often the end result of long-term algae or lichen damage that went untreated.
This is a structural concern, not a surface one. Sagging indicates the decking underneath has been compromised by long-term moisture. This is typically the result of moss or lichen that held water against the roof for years. Do not walk on it and call someone.
If water is getting inside, the growth on your roof has already done structural damage. Cleaning the outside won’t stop water from coming in.
While some asphalt shingle roofs carry warranties of up to 50 years, the lifespan of many roofs in Ontario is only 20 to 30 years.
If yours is in that range and you’re dealing with significant moss, algae, or lichen, you may be maintaining a roof that’s already in decline. Repeated cleaning treatments are an ongoing cost that a replacement would eliminate.
If you are unsure, a professional can tell you with a single inspection whether you’re dealing with a cleaning problem or a replacement conversation. An honest answer could save you thousands in the long run.
Here are some of the most common questions we get asked about roof cleaning:
What kills moss, algae, and lichen on a roof permanently?
Nothing kills any of them permanently. The goal is to clear what’s there and create conditions that slow regrowth. A bleach and water solution is the most effective treatment for all three. Zinc or copper strips installed near the ridge release trace ions that naturally inhibit regrowth over time. Combined with regular gutter cleaning and trimming back shade trees, this approach keeps most roofs clear for years between treatments.
Can I use vinegar to clean my roof?
Vinegar is sometimes suggested as a natural alternative, but it’s significantly less effective than bleach on any of the three growth types. It may have some effect on very light surface algae, but it won’t penetrate deeply enough to kill established moss or lichen. Stick with bleach or a commercial product formulated for roof use.
Is it safe to walk on my roof to clean it?
Only if your roof is in sound condition and you’re comfortable working at heights. Moss in particular makes shingles extremely slippery, wet or dry. Wear rubber-soled footwear, work with a partner, and keep one hand free at all times. Walking on shingles also puts direct pressure on them, which can crack brittle or aging shingles and dislodge granules. If you have any doubt about the roof’s condition, stay off it.
Will bleach damage my shingles?
Used correctly, no.
The key is rinsing thoroughly after 15–20 minutes, protecting your landscaping below, and not letting the solution dry on the surface. What damages shingles is scrubbing, high-pressure rinsing, and over-application, not the bleach itself.
How much does professional roof cleaning cost in Ontario?
Professional roof cleaning in Ontario typically ranges from $300 to $700 depending on roof size, pitch, and the extent of the growth. Lichen removal in particular can add time and cost due to how stubborn it is to treat.
It’s worth getting a quote alongside a roof inspection as a professional can tell you whether cleaning is the right investment given where your roof is in its lifespan.
T. Simpson Roofing Ltd. has been helping homeowners across Barrie, Newmarket, and the surrounding area protect their roofs for decades. Whether you need a professional cleaning, an honest assessment of your roof’s condition, or a quote for repair or replacement, we’ll tell you exactly what your roof needs.
Call us at 1-800-925-3044 or contact us here.
