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My roof seems to be growing moss and I'd like to remove it. I did some research and it looks like the solution is to mix water and bleach, spray the mix on the moss and then scrub the moss off about 30 min later. My concern about this is wont the bleach run off the roof and kill my grass? Or worse get into my septic tank or well water?

Is the bleach mix safe or is there another method?

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Why not simply see if you can spray the moss off with a hose and scrub off the rest? I'd only use chemicals if no other methods work. –  GdD Aug 14 '12 at 14:59
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This Question might be worth a look. This Question might also be worth a read, or more specifically this article that is linked to in the question. –  Tester101 Aug 14 '12 at 15:01
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3 Answers

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The bleach mix will be dilute enough that it will not be of harm. I've used it myself at least a few times to kill off algae that has accumulated.

You can also use things like Oxy-Boost and Stain Solver, a bleach substitute which I believe contains some hydrogen peroxide. It will also work against light moss and algae, yet perhaps be less harmful to plant life underneath.

More importantly is to fix the source of the moss. Roofs that gather moss tend to be too shaded, under big trees that stop it from drying out. You may need to open things up, just by a bit, but enough to let it dry out. Yes, those trees are a natural source of air conditioning, but trees tend to grow. So trim off branches that overhang the roof. Cut a few others out to let the sun in.

For roofs that have only a bit of green, you may find it is sufficient to add zinc strips along the top. The zinc leaches out, keeping the roof clean of moss accumulation. There are also shingles with a moss inhibiting additive that prevents moss from growing. Copper strips should also work, and copper flashing is easily available. I've even read that you can glue (use silicone) copper pennies just under the edge of the top row of shingles. They are mainly zinc anyway.

If the moss had accumulated heavily, the problem is your roof likely needs repair, as it will have been too wet for too long. The shingles will need to be stripped off and replaced, but probably the roof decking will be soft and need some repair too. This can best be judged by a professional who will inspect the roof carefully.

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I've also seen bare copper wire strung between two screws across a roof, one just below the peak and one halfway down. Over the years, just enough copper oxides leach off to knock the moss down. –  Fiasco Labs May 11 '13 at 16:27
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They make moss remover products for roofs. If you live in a mossy region, your local home and garden center will carry it. They are often in granule form that you shake on the roof, leave for a bit, then brush/sweep off.

If you has asphalt shingles, be wary of scrubbing too hard, you don't want to scrub off the shingle's surface.

Around here (PNW) zinc strips don't seem to do a whole lot. Maybe if the entire roof was zinc, it'd work, but for the most part, I see plenty of moss on the roofs that have zinc strips around here.

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Yeah, the zinc strips work on our home in the Northeast, but there are surely limits. –  user558 Aug 14 '12 at 16:07
    
Heh, PNW, winter gloom with lots of water. Lichens eat the metals and the moss thrives. The moss on the ground gets to be a foot deep if you're in the right areas. You're not going to keep it off a shaded roof, no matter how hard you try. A broom after summer heat is about the best you can do. –  Fiasco Labs May 11 '13 at 16:29
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Nothing works better than sprinkling dry Tide with bleach on the roof during a dry time. When the rain begins, The Tide and bleach will kill and remove all the moss and black lines. Do this every year, maybe when you clean the gutters. I live in the Northwest where this is a HUGE problem. It will not harm the plants or your house.

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