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?
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).
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
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?
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.
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