LESLIE: Dottie in North Carolina has a roof with some black streaks on it. Tell us about it.
DOTTIE: Well, it’s just those black streaks are beginning to form – I noticed it about last year or year before last –
DOTTIE: – are starting to get darker.
DOTTIE: And I was wondering what causes that.
TOM: Well, what it is is it’s roof moss or roof mildew. It’s like kind of a fungus growth that gets on there. And you get the spores that float around in the air and they land on the roof and they tend to congregate in the cooler places of the roof and that’s why you get the streak effect. So for example, if you look at it, you might see that right above where the rafters are there are more there than to the left or right of the rafters where there’s just plywood because the rafter tends to be a little cooler than the surface of the roof next to it; could be a few degrees difference. So that’s why you have that streak effect.
There’s a couple of things that you can do. Is your roof fairly shaded in terms of a lot of trees around it?
DOTTIE: No, sir. It’s completely sunny.
TOM: Completely sunny, OK.
DOTTIE: Morning and noon. (chuckles)
TOM: Alright. Well, let’s talk about a roof cleaner. Now, what you can do is you can apply a bleach-and-water solution and – you know, this is a pretty big project; it can be done with a pressure washer on a low pressure with a soap dispenser built into it. But you apply a mildicide; could be bleach and water, it could be a commercially-available mildicide, it could be a product like Jomax. And you saturate this roof and let it sit; the section sit for 10 or 15 minutes with this mildicide on it and then you can rinse it off and you’re going to find that it brightens it up very nicely.
Now, the second thing that you can do is you can add a strip of copper or nickel …
LESLIE: Or nickel.
TOM: … flashing across the ridge – all the way across the peak of the roof – and that will keep it clean. And the way that works is as the rain hits it, it removes some of the nickel or some of the copper and basically washes it down the roof and nickel or copper in the water is a mildicide. So that’s a way to keep it clean on an ongoing basis.
If you’ve ever like seen a chimney that has like bright streaks underneath it, that’s because of the copper flashing releasing some copper into the water and cleaning the roof as it rubs off it and runs off it and goes down the roof. So, that’s a way to do that.
DOTTIE: It has a cap on it but I’m not sure what it is. It’s sort of black-looking; the cap is.
TOM: You mean the cap on the top of the ridge?
DOTTIE: Yes, sir.
TOM: Yeah, well that’s probably a ridge vent and, if that’s the case, you can put this metal flashing kind of right under it and along the top …
DOTTIE: Right on top of it?
TOM: Well, not over it but like right under it.
DOTTIE: Under it, OK.
TOM: You basically want the water to hit it and run down.
DOTTIE: Oh, OK.
TOM: And you know, if you have a contractor does a nice job, it could all look like it’s part of the same thing because it’s all going to turn to a nice patina, you know, within probably one season.
DOTTIE: That sounds great.
TOM: Well, there you go. Thanks so much for calling us at 1-888-MONEY-PIT.