Published on September 5th, 2013 | by Henri


Metal strips to control algae on roof

Q.    Somewhere on TV, probably in “This Old House”, was a gadget to inhibit the growth of lichens on roofs. I have a lot and would like to get rid of them without the problems with Clorox all over. This gadget was a strip of metal with one of the metals, possibly one of the rare earths, an inhibitor for these plants. It goes in on the ridge pole and the needed metal leaches out, runs down over the lichen colonies and does them in. Very neat, tidy and easy.

I am reminded: if it is too good to be true, it probably is. Have you heard anything about this?

A.    The control of algae, moss and lichen on roofs is well-known in the northwest where the roofers use copper strips set just under the cap shingles on each side of the roof. In the northeast, we can see how these problems are controlled by looking at old barn roofs. Wherever there are galvanized metal roof vents, we see that the shingles below vents are as clear as the day they were installed. This is not the case on the other areas of the same roofs where algae grows unchallenged. The same thing is visible on any roof below copper or galvanized vents and flashings.

You have several choices. You can have a building or roofing contractor install a copper or galvanized metal strip snug against the bottom of the cap shingles or you can buy Shingle Shield zinc strips from The RainHandler and have them installed underneath the first course of shingles below the cap shingles, as per instructions. Home Depot and some hardware stores sell rolls of copper for the same purpose.

Copper is quite expensive; galvanized metal a lot less. You can order Shingle Shield on-line at Although Shingle Shield strongly recommends cleaning the roof of all growth before installing their strips, this is not necessary unless you are impatient and can’t wait for nature to take its course over several seasons. Having the roof cleaned with their solution is quite expensive.

If you have a ridge vent, you can have it replaced with Air-Vent, Inc’s zinc- coated ridge vent that, when it rains, leaches ions that poison algae and other growth. Any building supply store can special-order this ridge vent. But that’s more drastic than installing metal strips.

Be aware of the fact that these metal strips are most effective on algae — the unattractive black discoloration found on asphalt shingles throughout the country; they are not always as effective in the control of lichen and moss.

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