Your Shingles Have a Defense System. Algae Eats It.
Asphalt shingles are coated with small mineral granules, usually crushed slate or ceramic. Those granules do two important things: they protect the asphalt layer underneath from UV radiation, and they give the shingle its color and texture. Lose the granules and the asphalt dries out, cracks, and fails years ahead of schedule.
The algae that causes those dark streaks you see on roofs throughout Princeton, Pennington, and Hopewell feeds on the limestone mixed into asphalt shingles. As it spreads across the surface, it slowly strips away the granules that protect the shingles from the sun. You can't see this happening in real time, but over a few seasons, the damage compounds.
Moss Is the Next Step Up in Damage
Where algae is a surface-level issue, moss is more aggressive. Moss grows in thick patches and develops root-like structures called rhizoids that anchor it to the shingle surface. When those rhizoids work their way under the edges of shingles and lift them, you now have a path for water to get underneath.
In New Jersey and Pennsylvania winters, that trapped moisture freezes and expands, which accelerates the lifting and cracking even further. A shingle that's been under a thick patch of moss for a few years is a shingle that's letting water into your roof deck. We see this regularly on homes in wooded areas around Titusville and Lambertville where the shade keeps things damp year-round.
Lichen Is the Hardest to Deal With
Lichen is a combination of algae and fungus living together, and it bonds to shingle surfaces more aggressively than either one on its own. When lichen dries out in hot weather, it contracts and physically pulls granules off the shingle surface as it does. Over time this leaves bare patches in the asphalt that are fully exposed to UV damage.
Lichen also holds moisture against the shingle surface much longer than algae or moss, which accelerates the cycle of freeze-thaw damage through the colder months. It's the most damaging of the three and also the most common sign that a roof hasn't been cleaned in too long.
How Often Should You Have It Done?
For most homes in central New Jersey and Bucks County, PA, a roof wash every two to three years keeps algae, moss, and lichen from getting established. If your home is heavily shaded or surrounded by mature trees that hold moisture, leaning toward the two-year side of that range makes sense.
Regular soft washing on that schedule can realistically add five to ten years to a roof's usable life. When you compare a $2,000 cleaning every two to three years to a $10,000-$25,000 roof replacement, the math is straightforward.
Why Soft Washing Is the Right Method
It's worth being direct about this: power washing a roof is a bad idea. High-pressure water strips granules off shingles just as aggressively as lichen does. You'd be cleaning the roof by doing the same kind of damage you're trying to prevent.
Soft washing uses low pressure combined with a treatment solution that kills algae, moss, and lichen at the biological level. The organisms die and wash away naturally over the next few rain cycles, and the treatment leaves a residual barrier that slows regrowth. The shingles stay intact. That's what we use on every roof job.
If your roof hasn't been cleaned in a few years, or if you're seeing streaks, moss patches, or patches of gray where the shingles look thinner, give us a call at (609) 255-3787 or visit pleasantviewcleaning.co. We'll take a look and give you an honest quote.