Cleaning Algae from Cedar Shingles

 

DAVID: Well, thank you. You have a great program and I wonder if you could help me. I have a 20-year-old house with a hand-split cedar shake roof that I wanted to clean because it has some algae and dirt.

LESLIE: OK.

DAVID: I have mixed opinions: some say clean it, power wash it and then stain it; others say do nothing because walking on it, power washing it may do more harm than good.

TOM: So, David, are you concerned about the color, you know, the moss or whatever that’s on there right now? You don’t like the look of it?

DAVID: The color’s fine. It got dark; that doesn’t bother me. I’m just worried that perhaps the algae – a little bit of film of algae build-up might do harm. But everything’s fine. The roof is solid and doing well. But the painter wanted to also paint the siding or spray it – I wasn’t sure about that – but I find nothing that I need to do to the roof except worry that the algae might do harm over time. And I called up the Cedar Association and they say you could do more harm than good and so I got mixed feelings about …

TOM: Well, I agree and I don’t think it’s necessary for you certainly to put any kind of stain on there. I think that it’s actually …

LESLIE: You almost never put anything on cedar shake when it’s on the roof.

TOM: Exactly. Now, a lot of times folks don’t like the look of the algae and if that’s the case, you can clean it but when you clean it, I’d like to see you clean it by hand and not by hitting it with a real aggressive power washer unless you kind of back off on the pressure.

Cedar is designed to last a long time and the reason it wears out is when it gets too wet and the surface actually starts to degrade. So if you get up there and you’re really aggressive with it, then you can cause some damage. But if you’re worried about the algae causing something, I wouldn’t; as long as it’s not unpleasant to look at, you’re OK. I will give you one trick of the trade, though, that will stop it from growing some of that algae, some of that moss, and that is you can add a piece of copper flashing along the ridge, along the peak.

DAVID: Yeah.

TOM: And what happens is when it rains …

LESLIE: Or even nickel.

TOM: Or nickel. The water will hit that flashing and it will release some of the metal into the water. That acts as a natural algaecide and keeps the roof clean.

DAVID: Thank you.

TOM: You’re welcome, David. Thanks so much for calling us at 888-MONEY-PIT.