Clean an Asphalt Roof

Key Takeaways:

Black Streaks on Roof: The black streaks on Richard’s roof are likely caused by moss or algae, not mold. These growths are common, especially on the north side of roofs where moisture tends to accumulate.
Cleaning Solutions: To clean the roof, products like Zinsser’s Jomax, mixed with bleach, can be effective. Cleaning can be done manually with a scrub brush or using a pressure washer, but care must be taken not to damage the shingles.
Preventive Measures: Installing a strip of copper or nickel flashing along the roof’s ridge can help prevent future moss or algae growth. Rainwater running over the metal releases ions that act as a natural mildicide, keeping the roof clean over time.
Alternative Materials: Nickel can also be used as an effective alternative to copper for this purpose, and ridge vents made of these materials are available for easy installation.

LESLIE: Richard in Delaware’s got some mold on the roof. It might actually be moss but why don’t you tell us about it, Richard.

RICHARD: Hi. Yeah, I have a white shingled asphalt roof. And I have these black streaks and they’re maybe about 12, 14 inches wide. And they’re only on one side of my house, though. But it … I was …

LESLIE: Is it the north side?

RICHARD: The north side, exactly. And I went into a local store and they told me … I thought there was something that I could spray on it to get it off and there’s nothing I can spray on it. They told me it’s mold and I was surprised to even know that.

TOM: It’s probably not mold, Richard. As Leslie said, it’s probably moss. And moss will adhere … you know, the plant growth – the little seedlings that are out there – basically stick to the roof and they start to grow and that’s what forms those … the staining on the shingles. There are cleaning solutions that you can use for that. It’s a bit of a tricky job, only because the roof is, you know, up high and it’s pitched. So you have to be careful about what you use to …

LESLIE: Yeah, have to make sure you really feel comfortable up there.

TOM: Yeah, what you wash it down with.

RICHARD: (INAUDIBLE)

TOM: One thing that you could use is a product by Zinsser called Jomax – J-o-m-a-x – which is a solution that you mix with bleach and does a good job cleaning. And once you get the roof cleaned – and you can do it, you know, by hand with a scrub brush if you can reach it or with a pressure washer set very gently so you don’t like blast the shingles off.

RICHARD: Right, mm-hmm.

TOM: But here’s a little trick of the trade. After you get it clean, what you might want to do is take a strip of copper flashing and put it across the entire ridge – the entire cap of the roof. What that does is it causes … once the water – the rain water – hits it, it releases some of that copper and that becomes sort of a natural mildicide that goes down the roof and keeps it clean. A little bit of a …

LESLIE: Tom, is nickel also another option?

TOM: Yes. Yes. And in fact, you can buy nickel ridge vents and copper ridge vents, too, or you can just by the metal itself and just tack it up there along the peak of the roof so that the water – the rain water – hits it and just washes right down. And you know, if you’re wondering how this works, next time you’re by one of these copper flashed chimneys, take a look at the shingles underneath that copper flashing. You’ll notice they’re the cleanest shingles on the roof. Because the water hits the copper, it releases some of the copper, it runs down the roof and it cleans it.

So Richard, we hope that helps you out and leaves your roof sparkly clean. Thanks again for calling us at 1-888-MONEY-PIT.