Blog Update!
For those of you not following me on Facebook, as of the Summer of 2019 I've moved to Central WA, to a tiny mountain town of less than 1,000 people.

I will be covering my exploits here in the Cascades, as I try to further reduce my impact on the environment. With the same attitude, just at a higher altitude!

Thursday, November 6, 2008

Eco-friendly moss and algae removal

Roof mossI'm surprised that, after living in wet and rainy Seattle for so many years, we've never had a problem with roof moss before. I recently started noticing that a portion of our roof was getting a little green, even though it was in an exposed area that gets lots of daylight and no shade. Well, our roof is about 10 years old, so I guess it's time for the embedded shingle chemicals to stop doing their moss fighting duty.

So, what's a green homeowner to do about the green? Well, the classic method of treating moss and algae, whether on roofs or sidewalks, is good old-fashioned bleach. But, this is an environmental quandary since bleach presents all sorts of problems in general and, when used outside, causes even more issues specifically dealing with runoff into storm water drains and groundwater.

I've read that 1/4 vinegar to 3/4 water solution will kill the algae. Has anyone had any success with this or does it just come right back? Or is some sort of allegedly eco-friendly commercial product the way to go?

What about oxygen bleach? Is that just as harmful as chlorine bleach? What about zinc sulfate or zinc/copper strips installed on the roof line? Or do I need to just scrub the bejeezus out of the shingles?

Do any of you have any suggestions for an eco-friendly method of removing roof moss that someone can easily do themselves? Or is it just better to hire someone with the chemicals, the skills and a roof pressure washer to take care of business?

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Anonymous said...

Let me start by saying, I've never dealt with roof mold, so I'm just guessing here. That said, are you assuming that the mold is growing ON the roof? It could be that the mold's base is under the shingles. It's an awful thing to imagine but if there is plenty of sun in that area, the problem could be a wet underlayer that is manifesting as mold on top of the shingles. In any case, the Clean & Green book recommends vinegar, borax or tea tree oil for mold problems. Hope that helps!

Cave-Woman said...

Do the moss and algae cause any structural problems to the home? Or cause any health problems with the family? If not, maybe you can just keep the moss and algae and enjoy the green.

Jennifer said...

Just remember that the most sustainable method is the one that doesn't damage your roof, causing it to need replacing sooner. It does little damage (the only risk is that the moss or algae could hold water), and could be left in place. Also, when you reroof, look for shingles imbeded with copper instead of chemicals, preventing chemical runoff from teh room AND preventing moss and algae!

DON"T use a pressure washer under any circumstance, as they will likely damage the shingles, causing you to replace faster.

To keep the algae from coming back, insert 6-inch-wide strips of zinc or copper under the row of shingling closest to the roof peak, leaving an inch or two of the lower edge exposed to the weather. That way whenever it rains, some of the metal molecules will wash down the roof and kill any algae trying to regain a foothold on your shingles.

EJ said...

Copper runoff is a potential problem, too. Scrubbing will wear your shingles out faster. Leaving the moss in place will allow moisture to build up.

How quickly does bleach break down?

Jennifer said...

Another Jennifer here, Assuming the photo is of your yard, I would see what would happen if you scraped off as much of the moss as you can and then treat the roots with the vinegar solution. It can take a day or two for it to work. And it works best in sunlight. Who knows, a drop or two of tea tree oil may help there as well. Can't hurt.

I have no factual knowledge here, but I would be inclined to say oxygen bleach will not work on the moss on your bricks. I used oxygen bleach to clean our pressure treated wood deck and the surrounding plants were unharmed. Algae on your roof may be a different story. It might work, but scrubbing the shingles will cause damage so you'd have to resort to standing on your roof peak and dumping buckets of bleach mix down in the hopes enough of it stays long enough to kills the algae on it's way down. Not a technique I'd be the farm on.

And thinking about when I used oxygen bleach on the deck, it worked best on the dirt. The green gunk was looser but still needed to be scrubbed off.

We have vinyl siding on our garage and I've gotten the green gunk off of it with plain castille soap and water an a rag. Comes off like a charm.

That's what I know. Hope it helps!

Anonymous said...

I second the zinc strip, unless you are using the water from your drains for your garden. The zinc strip on our old house's roof did wonders. And that was here in the Seattle area.

Greenpa said...

Ha! The THWASPCO rules!

Moss buildup in the Pac NW can certainly become damaging. The Little House has no problems with it, though we're in the woods and shady- basically the very steep roof stays too dry for the moss to thrive.

The THWASPCO however, is a different matter; it's VERY shady, and has a much lesser pitch. And we need it to be transparent; the roof is clear fiberglas, to add heat to the processes.

What I have to offer is not a definite answer; but a really interesting observation: one side of the THWASPCO is shaded by an eastern red cedar (Juniperus)- and neither moss, nor algae, nor lichen will grow there.

There's rain drip on the roof, and also cedar needles fall and stay there until snow scrubs them off.

So what I'm thinking is, there's something in the cedar tree and/or needles that the moss doesn't like. Which makes excellent sense- if you're a cedar needle, you do not want moss covering you up; most similar needles stay on conifers for 3 or 4 years; plenty of time for moss to get going.

In your shoes, I'd do something drastic to kill and remove the moss (I'd try concentrated peroxide bleach first, and if it doesn't work- as little chlorine bleach as will do the job); then I'd try regular applications of conifer-leaf tea; as concentrated as you could make it in a blender, sprayed on the roof and allowed to dry. Hey, it's organic! And you wouldn't be putting anything into the world that the trees aren't already putting out.

It might even work. No moss- for years, on that side of the THWASPCO.

Anonymous said...

I'm not foolish enough to take on Greenpa on this sort of thing, but we also have an evergreen tree growing over one corner of our house and that is the mossiest corner we have. It doesn't get enough sun to keep the moss from growing. Also, the grass under our evergreens is more moss than grass.

So I'd guess that if you're going to try the evergreen tea, try it from an eastern red cedar like Greenpa has. I don't think just any conifer will do.

Greenpa said...

Heather t- I'm sure you're right- YRMV, as always. Very heavy shade, differences in average moisture, drainage rates- could easily trump what may be a modest growth retardant. And different tree species are bound to be - well- different. I'm so used to natural variability I tend to take it for granted that everybody just thinks that automatically. Which has gotten me into trouble before. :-)

Unknown said...

For the Moss we first kill it with biodegradable laundry soap. Just sprinkle it on. Wait a couple weeks (you'll need a stretch of dry weather) for it to get good and dead then take screw driver and gently pry the dead clumps off the shingles and sweep it off the roof. It probably isn't the best since the moss does eventually come back put it seems to do the least amount of harm to the shingles. When the roof needs to be replaced we are definately spending the extra money for metal. Good luck.

Robj98168 said...

Well shoot- I would hire a roof cleanier. they usually don't use any chemical, just a pressure washer. Other than that, you could try a biodegradable powdered laundry detergent- we have a guy at work swear by tide! Of course, I had a chemist at work tell me that Tide is the worst thing you can use for your laundry so I would imagine it can't be too good for your roof or after it comes out the downspouts. I had this same problem and did nothing... I had the roof reroofed.

Lisa Nelsen-Woods said...

Oxygen bleach/cleaner is made with hydrogen perioxide, not chlorine bleach.

I had to clean some garden tools after dealing with slime mold in my garden (which is just as sticky and fun as it sounds.) My source said I should clean my garden tools with bleach so the mold wouldn't transfer to any other part of the garden when I next used the tools. I asked if there was another more enviornmentally friendly option I could use and they suggested hydrogen peroxide.

I think oxygen bleach might be the way to go.

Anonymous said...

I"ve heard that Tide laundry detergent, sprinkled over the roof, will kill moss. Haven't tried it myself. We had one outbuilding re-roofed with asphalt shingles, made them put a zinc strip at the roofline, and it's kept the moss off. Out house has a metal roof, so no moss there either.

Anonymous said...

My advice is based on you wanting to do this yourself.

Also, I was in the roof cleaning industry for ages. Been there, done that & seen a lot of weird ideas (jumping to conclusions is universal I guess).

RULE NUMBER ONE - every chemical manufacturer says their product is environmentally friendly (and if you believe that...).

The lowest impact method is to gently remove the moss by hand. Use a piece of wood or an oversized screw driver as a tool when necessary.

Start by cleaning as high as you can from a ladder leaning against the gutter. Then you can get on the roof to finish (it's safer and more comfortable to stay well above the roof's edge).

Wither blow the debris off with a back pack blower or with a garden hose.

The easiest moss killer to apply that I know of is Safer Brand Moss and Algae Killer & Cleaner. It is mixture of vegetable salts and you attach the container to a garden hose and spray it on. Pretty simple and about $50 for the average roof.

Everything else is either pretty toxic, or spotty, or ineffective. This includes zinc powders, zinc & copper strips, soap, and the worst of all... bleach.

A commercial guy can't afford to take the time to be as gentle, and they will typically use zinc napthamate.

Over Coffee - the green edition said...

I was just surfing the web for an eco-friendly solution to removing the moss on our roof and found this blog posting. I was wondering if you had tried any of the suggestions and if so, if they had worked.

ranchhand said...

I had extensive moss/algae in a Victorian 105 year old home very shaded by 100 year old elms on Lake Michigan in Illinois. I took several gallons of straight Clorox bleach and walked the peak flooding the affected parts of the roof. Next day staining was gone, shingles looked new, and it has been 5 years and moss hasn't come back. No damage to shingles, gutters, downspouts, trees, decorative shrubs/flowers below, and the wonderful 100 year old green ivy growing under the trees on the East side of my home. The bleach stayed in the gutters and dried (there was not enough to actually run down the downspouts) and the first good rain we got diluted it and washed any residue away. That was 5 years ago.

Unknown said...

I have pressure washed several roofs in the the Eugene area with a low pressure setting and come out with fantastic results. People who say not to use a pressure washer do not know how to use one. Pressure washers are strong enough to go right through a wall if you put the jet nozzle on and aim at one spot but that would be stupid right? well so would using a lot of pressure while cleaning moss off a roof. You can use a large angle fan tip and come out with the best results out of any of the suggestions on this site. If you do not believe me look up before and after photo's of moss removal and you will see that ALL professionals use pressure washers to remove moss because they are professionals and they know how to use the tools of their trade.
Moss will ruin your roof by expanding and contracting over the years with the weather. The roots will eventually break down the shingles basically eating them. Zinc strips do not work very well if at all. I have uncovered zinc strips on roofs that were covered in moss.
Your best course of action is to treat your roof every six months. Using any of the several treatment methods mentioned. If the moss is crazy have it pressure washed off using a reputable company they do exist.
Do not use a screwdriver on your roof! People don't want you to use a pressure washer but they send you up there with a pointy metal object using it to pry or scape the shingles? Those are the people you do not want to listen to.