Sort of. But usually in streaks and the farther down from the strip, the less they work which is the reverse of what you actually need. They can also eat away your gutters, stain your concrete and poison your landscaping. (I wish I had a dollar for every roof I’ve been on that had moss growing out from under the zinc strip!) Then the run-off ends up in our rivers, lakes and streams. Check out the warning labels on some of the moss treatment stuff you can buy over the counter. (And that’s the ‘homeowner’ strength!) Some of them will make you feel like donating a year’s income to Greenpeace.