In this picture of a very moss covered roof it is very clear that the various galvanized plumbing vent-pipe penetrations are in fact reducing the moss growth in the areas beneath them.
In this next picture, the black algae discoloration---another type of vegetative growth that occurs on roofs----can also be affected by zinc given off by nearby galvanized components on the roof. In this case the chimney restraint brackets and chimney flashings are helping to keep the roof clear of algae in a distinctive pattern that corresponds to the bracket and chimney installation. It almost looks as if someone got up there and cleaned that area.
Left and right of the clean area you can see the distinctive marks of where someone has pressure washed the roof---but not really consistent with the area cleaned by the zinc from the galvanized components.
So why don't we see more zinc strips on roofs?
I think the main reason is because they are "unsightly"----people don't like the way they look and if they aren't installed about every 3 feet on the roof they will not keep the entire roof free of moss & algae growth. Note how in the second picture the roof is only "totally" clean about three feet below the bracket?
I know you are waiting for my recommendation for an easy solution----but alas I have none. Some roofing materials supposedly have zinc granules included in the roofing materials itself, and the effectiveness of this approach has yet to prove itself to me. It would seem to me that these roofs would stick out like a sore thumb in the NW but I have yet to see this. As near as I can tell the algae doesn't represent much of a problem for the roofing materials itself----unlike the moss which should be controlled. Sweeping the roof during the dry season seems to be effective. Pressure washing should always be avoided as it will take far more years off the life of the roof than sweeping will.
The most important thing I can say about moss on your roof?----be careful up there. Only people experienced to work on roofs should do maintenance work on roofs.
Charles Buell
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My WORDLESS WEDNESDAY pictures and some selected POEMS & STORIES.
Charles, Here in Maryland we do see the dark roofs like in your second picture. I've never seen anything like the first picture though. That is unbelievable.
Richard, while this one is particularly bad----it is what would happen to any roof in the NW if they aren't kept clean.
Are there many people with metal roofs in the NW? Wouldn't that make sense if there is such a problem? I too have NEVER seen moss grow on a roof. Of course living in Georgia all my life I am sure that there are many many things I haven't seen. I can't stop looking at the picture. Funny thing is... I recently saw someone making grass grow on their roof on purpose on TV. They called it "green". They should have just moved to the NW. And Charles, what does the moss do... shorten the life of the roof or actually cause leaks? I find it pretty. Maybe not practical, or smart, but still pretty.
Tammy, the moss will feed on the cellulose component of some asphalt shingles and obviously feed on wood ones. What happens is it starts to grow under the shingles breaking the stick-down tabs leaving them vulnerable to wind damage and wind driven rain.
Looks like my garage roof. Not sure why it grows there and not on the house roof. Only one side too.
Pic 1 is classic. I have never seen anything so extreme. Sure it wasn't a tree bark roof?
Jim, is the garage more in the shade than the house?
Jack, I wish I could say that I never see these----they are all too common. Especially detached garages.
No, not really. Actually the side with the moss is the sunnier side. Kind of weird....I know
You may need to call Ghost Busters:)
Ah, the moss covered roof, a common sight in the PNW. I thought Portland had a lot, but out in the country, they seem very common. Of course, so are mice living in the walls....
Kim, I am sure that Oregon and Washington are pretty similiar in this respect.
Charles I am having the same problem with my home and it is really annoying. I was told it was because last summer we had such high moss pollen. I just have alot this year...
Charles, just a matter of note. Trying to read the blog first was a chore of scrolling back and forth. Clicking on comments made it readable. Strange. Also strange is that roof. That is a common roof where you live? How often does one have to clean that stuff off?
Paul, I hadn't noticed any difference.
Barbara, I have no idea why it is doing that----doesn't seem to be anything I am doing.
Are zinc and/or galvanized products required there so home inspectors can see a portion of the shingles to make a proper roof identification and commentary?
Seriously, when there is so much moss on a roof, do you make any recommendations? I simply don't see that around here. It would be informative to know what you "Norwesseners" do about it.
Jay, when they are as bad as the first picture about all you can do is recommend that it be properly cleaned and evaluated further:)
Do you ever recommend zinc-based chemicals for moss removal?
Vince, I really don't have any experience with those products. I suspect that they should work at least temporarilly.
Around here we get small amounts of moss, more like algae really, and a black spore which looks like minute amounts of tar dripping down the roof.
Recently I have recommended a product called "Spray and Forget" to my clients for those problems, and on siding as well. But what in the world can you do for a hairy beast like the roof in your photo?! And what can you use that won't kill shrubs and grass below? Thompson's makes a pretty good oxygen-based product, but I suspect it would require a lot of scrubbing for your moss. How do they do it?
Don't see moss that thick around here. Do see the black algae quite often. I have been told by a roofing manufacturer that the black algae is a direct result of the grade of asphalt used in roofing shingles now.
Jay, out here you just have to keep ahead of it. Brushing the roof during the dry season does a pretty decent job. Unfortunately a lot of people resort to pressure washing which is worse for the roof than the moss in my opinion. Some---and it works----sprinkle Tide along the ridge.
James---that wouldn't surprise me. Have you heard anything about some of the granules of asphalt roofs being zinc?
A roofing company around here told me that the black drippy stuff is a spore, making its way north or south, I don't remember which. I have examined the spots up close and sometimes it does appear that there is a small hole through the granules that bleeds some asphalt through, so there may be something to that grade thought James brought up.
Power washing the roof?! Yikes! I tell my clients not to power wash anything except maybe a concrete patio and the driveway... Wow, when the moss gets that thick it must be a real job not to damage those shingles. Brushing I would think also damages the shingles. Have never hear of the Tide technique. Can't hurt probably!
Not zinc but copper blended into the granules. I believe it is referred to as mold or moss resistant.It carries a short guaranteeof about 5 -10 years. After which time the copper has bleed out and is no longer effective.
Had another guy who gave a seminar on roof cleaning. Told us that right about ten years is when the black algae stuff will start growing on a roof. Like in your second picture. I have seen the same thing here behind copper flashing. Clean for a few feet behind the copper.
You can buy powdered zinc. I have used it and it does a pretty good job. The catch is that it has to be applied during the moss growing season (aka rainy winter). This makes it more dangerous to the amateur roof cleaner. I don't like brushing in the summer for the same reason I don't like pressure washing. It also removes granules and shortens the life of the roofing material. In my experience, moss grows way better on the North side, but given proper conditions, it can grow anywhere, including on metal roofs.
Jay, yes, pressure washing should be avoided on roofs.
James, it is pretty tough to keep this stuff off of roofs.
David, you remind me of another point about asphalt shingles----in them selves they are a poor choice of roofing in the NW. We can spend a lot of time trying to find good solutions to cleaning them but no method beats not using the stuff to begin with:)