Leave it or remove it?
I am getting conflicting advice. Some say do not worry – leave it, it will not harm it. If you pressure wash it off it will also remove most of the granular which protects the shingles
Others say the pressure washing will not harm it
Some suggested the install a zink strip on the ridge; it will kill the moss but it will also discolor the roofing material
What will moss on the roof do over the long run?
Any comments?
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Replies
the obvious is making it very slippery should you have to go upon the roof for any reason.....the moss will eventually grow in such a manner as to lift and curl edges so moisture could become a larger problem...collect more debris, depending upon climate allowing snow/ice to accumulate and further deteriorate the roof...more curling allowing wind to lift the shingles, etc.......
that's why 3tab has the adhesive under the front edge...to keep the surface tight and as smooth as possible
but, I am not a roofer...take it with a grain of salt
First off, is it moss or algae? Moss had thickness and occurrs in patches, algae discolors without adding any significant thickness to the shingle, and it occurs more in streaks.
Chlorine bleach solution will kill either (but is more effective on algae). There are some other chemicals (herbicides) that are effective on moss. Keep all chemicals (including bleach) from hitting grass or plantings around the house (tie plastic bags to downspouts, eg).
Zinc strips are effective against both (again, more effective against algae) and will not discolor the shingles (at least not that I've ever seen).
Usually when moss gets started it means that the shingles are beginning to go anyway -- the moss gets its foothold in tiny cracks in the shingles. But moss will accelerate the deterioration.
Trees overhanging the roof tend to encourage moss (but not so much algae).
Pressure washing is hard on a roof, especially one that has begun to deteriorate.
The glue strips on shingles are there primarily to prevent blow-off.
Another option
I sprayed this material onto 2 customer's roofs this spring, two sides of a duplex. I sprayed one and waited to see results, then sprayed the other.
Neither roof had what I would call "heavy" moss growth - more like small patches of a few square inches each scattered about the roofs.
http://www.wetandforget.com
Slow acting, no scrubbing, 8.0 pH, no need to rinse roof or gutters, no need to cover nearby plants, relatively inexpensive - $100 or so for the chemistry to do both roofs.
The product kills the "furry" green types of moss very well, then wind and rain removes the dead moss. I used it on asphalt shingles and brick walls.
Do not be tempted to "spot spray" - I tried that on one smallish roof plane, ended up going back and respraying that entire plane. I speculate that the material slowly washes down the roof and keeps "re-treating" the lower sections of roof where the heavier moss population typically resides.
Jim
PS: Looks like you will need to buy the material in Blane or Ferndale, WA, USA, and import it to Canada.
Moss will cause water to be retained. Freeze/thaw cycles will not be good for your roofing. It can also promote leaks by allowing water to back up ... much like ice dams. I used a zinc strip on my north roof ... notorious for having moss clumps on it. The zinc didn't seem to be a huge success for me.
Can't leave moss there. Like the other guy said ... makes it heck to get up on the roof, too. I manually scraped mine down w/ a putty knife. Wow that was a job. Live and learn.
This on your house or barn??
My barn (outside Seattle) has 3" thick covering of moss on both the 3/12 and mansard sides. Barn is 35 years old, same roof, still does not leak, 3 tab asphalt roofing.
After about 10 years the moss is so thick under the trees that you can grab a handfull and it all comes up in a big blanket, but most of it I've jsut let be.