We had a new roof put on three years ago and now have moss like we never had with our old roof. I’m guessing that the 125′ Doug Firs growing near the house (and overhanging portions of the roof) are not helping.
In the past, I periodically pressure washed the old roof, but noticed afterwards that it took off some of the surface particles imbedded in the asphalt. So, I stopped the pressure washing. I’ve used a leaf blower on a regular basis to clean off all the debris that falls on the roof from the trees (needles, cones, seed casing, twigs, etc.), but this obviously doesn’t remove moss.
Now that it’s starting to rain, the moss has come back with a vengence. If I could level out the roof, it would make a great putting green.
Someone mentioned installing zinc strips on the top of our shed roof, but warned that the zinc loses it’s potency as it travels downward and might not have much of an effect on the moss lower down. Also, what does the zinc runoff do to the vegetation around the downspouts?
Still others have suggested that moss, besides looking unsightly, doesn’t really harm the roof. Even if that’s correct, I guess I’d rather have it off the roof than on.
Any suggestions would be most appreciated.
Replies
Moss or algae? Moss has discernable thickness (maybe 1/32 to 1/8 of an inch) and is fairly green when growing, brown to black when too dry or cold. Algae just has a dark green to black color with no visible thickness.
Zinc (or copper) is quite effective with algae, moderately effective with moss. Both can be killed (and the staining eliminated) with a solution of FRESH chlorine bleach, but protect plantings from runoff. Moss (but not so much algae) can also be killed with certain herbicides.
Zinc strips can't hurt. There isn't enough runoff to damage plantings. And if having strips along the ridge doesn't do the trick all the way down you can always add another row along the middle.
Algae is "mostly" harmless, but moss will damage the roof eventually, getting into microcracks with its roots and widening them.
If your old roof didn't have the problem then likely the shingles had zinc or copper in the granules.
Thanks for the post, Dan.It's definitely moss, not algae. I've been reading that zinc strips lose their potency becoming less and less effective over time. I'll try the bleach. When you say "solution," I'm assuming I don't put it on full strength, but dilute it with water? My guess is that it's best to put this on in the summer when it's less robust and the rain won't dilute the solution. It's so bad presently, I might consider pressure washing it off just this once.Thanks for warning me about the moss, I didn't know it can eventually damage the roof.
redoak,
Sprinkle the roof surface with "Tide" granular clothes washing detergent (the one that has a bleach in it.)
Thanks, dovetail. My wife wants to know if it's biodegradable? She wonders what the effect will be on the shrubs, plants, etc. around the downspouts? My guess is not great. Someone should create a bacterium that loves moss.
redoak,
yes it is biodegradable. Effect on plant growth should be nil. You don't need to use a lot of it, lightly sweep or use a blower to clean the loose stuff off the roof then sprinkle the detergent across the roof. My roofer told me about this technique and I know it works from personal experience. I concentrate on using it in the areas most affected. Another technique is to string copper wire across the roof periodically, say every 8'/10' up the slope. . That is if you can afford the copper wire . I used to salvage house wire just for this purpose before the cost of scrap so high.
They can't get your Goat if you don't tell them where it is hidden.
Another vote for the Tide with bleach. You need to have several days of sun so that it has time to work before being washed off. Many roofing manufacturers recommend it as their preferred treatment as it does not harm the shingles. I have not seen any affect on plants around the downspouts. Because it is a bit sticky when wet, it takes quite a lot of rain to completely wash it off, so only a very diluted concentration comes through the drains at any given time.
Thanks, fingersandtoes,I'll try the Tide with bleach. Sounds like a good way to go. I'll give it a try first before going for the zinc strips.I appreciate your post.
another proponent of the Tide approach - an unfortunate characteristic of our climate is it contributes to being a wonderful host to such maladies
found a light touch w/ flathead shovel better than pressure washer on roofs but that is one coming from someone w/ a definite bias against pressure washers on roofs or any wood flatwork
the shovel just to get the grossest layer of moss off then hit w/ Tideam amazed Junkhound has anything good to say about zinc strips unless he found some testosterone packed jumbo size strips at the Boeing surplus yard because I've installed some, observed many more and haven't seen a positive result in one circumstance in more than 30 yrsif your roof is a tough go to be on there are some good yard long pumps where a hose goes into a five gallon bucket of the solution & they'll shoot almost to Junkhound's roof from yours
I'm 25 mi south of you in Renton with lots of DFir around the house.
What is your roof slope?
Mine is 3/12. Did a reroof about 7 years ago and installed 2 each 2-1/2" wide zinc strips on each side. Previous experience was that a zinc strip that width is good for only about 8-9 feet of roof at low slope, probably less at high slope.
Sweep the roof off probably 4 times a year (2160 sq ft) and pressure wash with wide nozzle every other year. Even built a set of stairs to the roof to be able to keep the trees, and gutters accessible from the wrap around deck. The zinc keeps the moss spots down to manageable level - a must to get the decomposed needles off a low slope roof at least yearly or you will have plants growing on the roof besides moss.
Ferrous sulfate, copper sulfate, bleach, etc, just wash off too fast out here to be any help, tried 'em all - zinc or copper strips your best bet.
Galv. works too, but is only good for 5 years or so, original galv gutters rusted thru in 5 years due to the acid of
the fir needles.
Barn is original 3 tab roof, 9/12, 35 yrs old, it has 6" thick moss in places but still does not leak <G>.
View Image
I installed over 1000' of zinc on the painted metal roofs of a shopping center over 10 years ago. I didn't think they would work but the owner insisted. It was time consuming and expensive. I couldn't tell any difference a year later and still can't see any difference now. I mentioned that it was painted because the white paint makes the mildew easy to see and would make any cleaning from the zinc very apparent. Look at the lead boots on your roof. How far down the roof do they bleach out mildew?