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I have an old house with a new(er) installed roof shingle that's about 5 years old. In removing leaves from the gutter today, I noticed green moss? mold? around some of the areas close to the house. A couple of questions:

  1. Should I worry about this? (does it reduce the effectiveness of the shingle). If yes, then question 2 come into play.
  2. Can it be corrected in the area that are truly unsightly with a chemical or something? I have kids so it would need to be safe. If yes, question 3 comes into play.
  3. If some cleaning can be done to fix, is this a DIY or does a service have to be contacted?

Once corrected, is there any preventative measures that can be done to avoid this?

Appreciate time in advance for your thoughts.

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3 Answers

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Should I worry about this? (does it reduce the effectiveness of the shingle). If yes, then question 2 come into play.

There's certainly more important things to worry about in life, but, yes, Moss will, over time, shorten the lifespan of asphalt shingles.

Can it be corrected in the area that are truly unsightly with a chemical or something? I have kids so it would need to be safe. If yes, question 3 comes into play.

Yes. Actually, you want to correct it over the entirety of the roof. You can purchase spray-on as well as granule based moss killer. That is what you want.

If some cleaning can be done to fix, is this a DIY or does a service have to be contacted?

You can DIY or you can hire a service. If you live in a moss-friendly region (such as the Pacific North West of the USA) then you'll find all sorts of people that do pretty much just this. Either way, be sure to hire people that use very gentle cleaning methods. You don't want power washing or anything of that sort.

Once corrected, is there any preventative measures that can be done to avoid this?

The only real remedy is to not shingle a roof with asphalt shingles in moss-prone regions. That's why you see a lot of standing seam metal roofing in wet areas. Barring that, you just need to make the moss prevention an annual chore.

Some claim that zinc strips will work (as zinc will kill the moss) though, at least around here, you can find plenty of roofs with zinc strips that also still have plenty of moss on them, so I tend to think that's a bit of a scam solution.

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I tend to think that people that will have you worry about moss on your shingles are selling a scam. Many of my neighbors have had shingles for 20 years or more that have mossy spots and never once attempted to correct this. I would think the shingles have a shorter life because of the exceptionally moist environment that just so happens to be friendly to moss. –  maple_shaft Oct 22 '12 at 11:36
    
Around here, mossy spots are rare. It's typically a full green carpet. I admittedly don't know how much damage it really does. On bad roofs, though, the moss is acting more as a 'net' for other organic material to built up and you sometimes can find full plants growing amongst the moss on a roof. –  DA01 Oct 22 '12 at 14:42
    
That does sound exceptionally bad. I would think anything that would be able to grow roots could in fact burrow through shingles, but I have never seen moss quite that bad around here. We usually get it in small spots on the roof and the consensus is to ignore it. –  maple_shaft Oct 22 '12 at 14:54
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Should you worry about moss on asphalt shingles?

The moss itself, not so much. The reason the moss is growing is the bigger problem. Moss, like mold prefers damp conditions. This dampness could be a normal occurrence in your location (very rainy location), or because the roof has too much shade cover.

Damp location

If you live in a damp location, where the sun just does not shine enough to dry out the roof. You'll want to find a moss killing product, and apply it annually or even biannually depending on how fast the moss grows. A gentle application process is best. You won't want to walk all over your roof twice a year, and you defiantly don't want to power wash or brush your roof often (if at all).

Too much shade

While shade can be great for keeping a house cooler, it can also be great for aiding in mold, moss, and mildew growth. In most situations, a few hours of sun a day will dry up excess dampness (rain, dew, etc.) on the roof. If there is too much shade on the roof, the dampness will not dry naturally. The best thing to do in this situation, is to remove some of the shade. This is usually achieved by trimming, or cutting down nearby trees. You likely won't have to remove all the shade, just enough to allow the sun to hit the roof a few hours a day.

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Actually, there's a great suggestion in one of my favorite general-knowledge renovation books about how to prevent moss growth. This is a much more permanent way to solve the problem, IMHO.

Tack up a line of copper wire (not zinc) just after the first line of shingles (close to the top). Copper is bad for plant life, and so the slight copper solution from rain washing over it will kill off moss. Obviously the wire needs to be bare, so if you're using scrap, be sure to give it a good wipe with 80 grit sandpaper before putting it up. Sorry I don't have the book in front of me, so I can't name the page number or quote it precisely.

Of course, take care tacking up the wire to observe common-sense principles about putting holes in your roof. Depending where & how you attach the wire, you might want to cover the nails, staples, etc with roofing cement.

Also, while this solution makes sense to me, I haven't used it. I'm basing my suggestion on the stellar reputation of this book.

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FYI, Amazon says that there's a 4th edition of that book out now. –  Niall C. Oct 23 '12 at 15:35
    
@Niall C - Technically it's not even out yet. Great find! Thx! –  pbarranis Oct 23 '12 at 19:50
    
I will take a look. I am a bit worried about adding any holes to the roof, even with compound. that stuff seems to shrink and fail over time. I live in New England and have many shade trees and eves that this stuff grows in the shadow of. –  Carl B Oct 24 '12 at 13:32
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