Green growth on North Side of new roof?

[captmikey]

I had a new roof put on three years ago, and spent the extra money to get the 50 year top of the line product. The work was great, the roof looks great... except in one area in the front of our house where one soffet overhangs about 5 feet of roof from the room below. This is on the north side. We've even cut back the bigger trees last year so nothing is overhanging the house.

So how do I rid myself of this green growth. It's almost microscopic, and not moss. It could be a green mold maybe? But should I try bleach or boraxo or what? I have a 2300 psi washer, but I know that this would be a no-no. Ideas?

Mike

[Travis Jordan]

Roof material? If it is 50 years I'm guessing tile. Or metal?

[Dorot29701]

Don't know where you live but here in FL it is common for algae or mildew to grow on the north side of the house (or wherever the sun doesn't hit until later in the day). We have a man who comes around once a year and sprays the roof with mildecide. Or, if it's not too bad - you can use sprayer (like for insecticide) and spray Clorox to remove stain. You can buy mildecide at Home Depot and spray that, too. It usually removes the stain plus prevents (or helps keep it from coming back for about a year).

[Doug Kanter]

Next contestant! The roof's not 50 years old, it's 3 years old and the material has a 50 year guarantee.

[Travis Jordan]

I didn't say it was 50 years old. I said "it" (the warranty) was 50 years.

[Doug Kanter]

One of us is mixed up, and there's a 51% chance it's me. :-) Gotta stop doing 12 things at once.

[Roger Taylor]

Green algae and/or fine moss is common on sheltered n-side roof exposures. Several ways to treat - easiest is spray bleach if it is a small area. Will have to be reapplied every couple of years. Also, Home Depot sells a zinc solution for moss and algae, to be diluted then sprayed on, but it is fairly pricey and toxic to other plants. I control moss formation, once roof is cleaned, with a strip of pure zinc metal at the top of the slope, but if rain does not hit at the top slope, this wont work, as the method relies on rainwater leaching out zinc ions from the metal, and spreading them downslope...

[captmikey]

First... I have to end the confusion. The roof is 3 years old, and it has a 50-year guarantee.

Sounds like the home method of spraying some bleach in a pump sprayer should do the trick. We were concerned that the bleach might affect the base color of the actual shingles. Would a 50/50 mix be appropriate or full strength?

Mike

[Travis Jordan]

Shingles.

OK then -

Avoid chorine bleach as a roof cleaner. Chlorine bleach can discolor shingles or shakes, it can kill vegetation on the ground if it runs onto the ground as it is rinsed from the roof and it can accelerate corrosion of metal gutter and downspout systems. Use non-toxic oxygen bleach. The bleach powder is mixed with water and applied to a cool roof surface, preferably on an overcast day. If you keep the roof surface wet with the solution for just 20 minutes and then lightly scrub the roof surface, green algae almost always comes off.