Next time you see a wood or asphalt roof that is furry with moss, mold and fungus, look around the chimney flashings. You’ll probably see that there’s nothing growing on the shingles in areas where rainwater washes across the copper or zinc flashings, and then onto the shingles.
The same protection can be had on the entire roof by slipping pieces of zinc or copper flashing under the top row of shingles. Leave about half of the flashing’s width exposed to the weather. That way rainwater can run across the metal and kill that nasty roof vegetation.
Jefferson Kolle, Ridgefield, CT
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Makes me wonder about metal flashing and the safety of collecting rainwater for drinking.
zinc strips only work for the first 3’ of the roof from the peak. Have tried to use them for years. Expensive and do not work!
While moss can come back, the easiest way to kill it for long periods of time is to brush on slightly diluted Joy or Dawn dishwashing detergent. Don't brush the shingle too hard, just slightly. Leave it on, don't rinse. The moss will be gone in a week or so.
creinckens: There is a 75 year old milk house near me that has a roof completely free of moss & algae directly downslope of the central chimney. In that case it has been effective.
firewoodworker: Some zinc in our diets is necessary. We've been using galvanized steel or iron pipe for decades and it only seems to be troublesome in very low pH conditions. EPA's limit is 5 ppm. I don't know the means to determine what concentrations result from rain washing over a zinc strip on the roof, but I can't imagine it's very high.
Ct yankee- is their growth on other portions of the roof? As a professional, have done roofs with many different zinc materials,I can tell you that it works on the first three feet, from the peak of the roof. I have not installed every three feet, if I did the houses would look like landing strips!
Having used copper under ridge shingles, it worked great, parts without copper had moss growth.