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Algae stains on roofs


Neal Lewis
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I got a call that a buyer's insurance company has stated that the "mold" on the roof has to be removed or the insurance policy is canceled. The buyer has moved in and wants to know why I didn't know that their insurance company would require this.

Has anyone else heard of this insurance requirement?

Do you guys just report on the stains or do you recommend cleaning/removal, or what?

Would anyone wish to share their verbiage about algae stains on roofs?

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Hey Neal,

You don't even want to know my response to the "Why didn't you know our insurance company would require this" thing... I'm in a mood and might say something inappropriate. [:-censore

I have this .pdf file that I include with my reports.

Download Attachment: icon_adobe.gif CASMA - Techincal Bulletin Roof Staining Algae.pdf

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The algae is aesthetic only. Tell the insurance agent to go jump off the roof.

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That algae is a regular occurrence around here and really, depending on how long it has been on there, the "stain" may not come out. Just explain to your client that it is not mold, but algae. They can try and use Moss Out, but the algae will more than likely return They could also apply a zinc strip to the ridge and that might help. The blue green algae, is from an airborne source and real common in humid areas.

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I've never heard of an insurance company requiring algae be removed. I think if pressed, they'd have a hard time coming up with published validation of their position. But then they don't have to - they're the insurance company.

Moss and lichens can damage an asphalt shingle roof. That being said, I have lichens on a corner of my roof, and I'm not doing anything about it. Still, when I encounter it on a roof I'm inspecting, I do recommend having it removed and if possible, eliminating the shade that helped it grow.

But you asked about algae. I always point it out to the buyer, just so they don't move in, wonder what that black stuff on the roof is and call me. Here's what goes in the report:

The asphalt shingle roofing has discoloration on the surface. This is algae and is mainly a cosmetic issue. There are ways to reduce or eliminate this condition. See Article 3C.25 for more information.

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Hi,

Zinc straps are a waste of money. They work for a few feet but after that their effectiveness weakens. If you want them to be effective, you need to install them every few feet. Moss and algae, like humans, use acid to consume their meal - oxalic acid - the same stuff one would use to clean concrete. If it's powerful enough to etch concrete....?

There are alga that literally eat limestone and some roof manufacturers use limestone granules in their protective granular coatings. If moss and alga couldn't harm roofs, why would roof manufacturers go to the extent of developing alga-resistant shingles? Surely not just to keep the roof looking pretty - anyone can do that with a roof cleaning solution; it's not necessary to spend untold millions developing alga resistant formulations.

I'm not a chemist, but after many years of looking at what moss and alga do to asphalt covers, I'm convinced there is good cause to get both off the roof.

Where moss grows and is ignored, the granules easily separate from the shingles along with the moss when the roof is eventually cleaned. I've noticed that there is a noticeable corresponding hardening or brittleness of the shingle material where the moss grows. I've noticed the same hardening where alga stains are left unattended for extended periods of time.

Roofing shingle manufacturers can call it "cosmetic" all they want - my experience has shown that it's not just cosmetic and I'm convinced it's bad for the cover.

ONE TEAM - ONE FIGHT!!!

Mike

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There's gotta be some regionality to it, I'd guess. I see algae and moss around here, sometimes for years on my own roof, and it doesn't hurt anything all that much.

You guys have algae on your roofs? What's that?

[;)]

Actually, we do have a limited amount in extremely humid, shady areas. But it is not any real problem.

I have a standing disclaimer that "I do NOT inspect roofs for insurability..."

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There are alga that literally eat limestone and some roof manufacturers use limestone granules in their protective granular coatings.
That's the same statement on literature from companies that sell all the crap to treat roofs that have black streaks. It also now appears on thousands of websites of roofing contractors, cleaning services and hundreds of home inspectors. Even homeowner associations are distributing this nonsense in bulletins.

Moss and lichens can damage a roof. What's causing the black streaks does not.

What's causing the dark stains is gloeocapsa magma. Everyone calls it algea, but it's really a species of cyanobacteria. It's a strain of photosynthesizing bacteria and it's "food" is water and the nutrients in rainwater, primarily nitrogen.

It's ugly, but it's NOT EATING THE SHINGLES!

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Various other opinions on this topic. Apparently the alga is a bacteria and not a fungi. One article talks about how bacterie a stimulated by limestone. Interesting stuff - lots of different opinions.

http://en.wikipedia.org/wiki/Gloeocapsa_magma

http://www.askthebuilder.com/082_Black_ ... gles.shtml

http://www.gaf.com/Content/Documents/111115.pdf

http://horace.wikidoc.org/index.php/Gloeocapsa_magma

http://www.inspect-ny.com/roof/Shingle_Algae_Stains.htm

http://ezinearticles.com/?Natural-Ferti ... id=1459239

All you have to do is examine a roof with severe alga streaking on it out here to understand what I'm talking about. There is most certainly a difference in the flexibility of the shingles and the granule coating is almost always thinner where the alga is concentrated - even without moss.

Still convinced the alga, moss and lichen does damage roof covers here - don't know how it performs elsewhere.

ONE TEAM - ONE FIGHT!!!

Mike

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Originally posted by hausdok

Hi,

Zinc straps are a waste of money. They work for a few feet but after that their effectiveness weakens. If you want them to be effective, you need to install them every few feet.

I think I have to beg to differ with you on that one.

Click to Enlarge
tn_20098221714_WoodShingleRoof.jpg

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All that clear area down to the eaves from that little Copper cap at the peak. Personally I think Copper works better then Zinc but they both work.

I have a house that faces my yard, heavily wooded and the shingled roof looks like a green shag carpet with moss. All except the completely clear area directly under the skylight that is flashed with Copper, Clear and clean all the way to the gutters, probably around 12', hell the edges are even crisp like someone ran a lawnmower through it.

Comparing Moss to Algae is like elephants and ameba's... Yah, moss around here can do a real number on a roof if let go. The fungus we have is even worse, but I've never seen damage or wear from the black staining algae.

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I have a house that faces my yard, heavily wooded and the shingled roof looks like a green shag carpet with moss. All except the completely clear area directly under the skylight that is flashed with Copper, Clear and clean all the way to the gutters, probably around 12', hell the edges are even crisp like someone ran a lawnmower through it.

Comp or wood shingle?

Here I see that happening with shakes and wood shingle but not with comp. Here, it seems to work for 3 -4 feet and then peters out on a comp roof but will keep the roof clear to the eaves on shakes and wood shingles. I think it's got to do with absorbency; the wood cover absorbs the stuff leaching off the copper or zinc but the comp doesn't - at least not what I've been seeing here.

I suppose there can be different varieties of mosses and alga that are adapted to various regions that react differently. If there are, I can't imagine what it takes for a roofing manufacturer to reach an acceptable balance.

Still convinced the stuff does damage roof covers.

Bill, for the record, I hate roof cleaning companies. If I were King of the Planet, the state would issue home inspectors seasonal hunting licenses and allow them to thin out the roof cleaner herd once a year. Every inspector would have a 2-kill limit. Inspectors would be lauded as heroes for doing a service to humanity. [:-devil]

ONE TEAM - ONE FIGHT!!!

Mike

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I see algae pretty often in my area and I do note this in my report. I classify the algae staining as mostly cosmetic, although moss growth can damage over time. I've also never heard of an insurance company caring about mildew/algae on a roof. When I see algae, I verbally suggest a product such as Roof Reviver which works well in cleaning this stuff off gradually, and also mention that when it comes time to re-shingle, thet may want to use an "AR" shingle.

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I have a house that faces my yard, heavily wooded and the shingled roof looks like a green shag carpet with moss. All except the completely clear area directly under the skylight that is flashed with Copper, Clear and clean all the way to the gutters, probably around 12', hell the edges are even crisp like someone ran a lawnmower through it.

Comp or wood shingle?

Here I see that happening with shakes and wood shingle but not with comp. Here, it seems to work for 3 -4 feet and then peters out on a comp roof but will keep the roof clear to the eaves on shakes and wood shingles. I think it's got to do with absorbency; the wood cover absorbs the stuff leaching off the copper or zinc but the comp doesn't - at least not what I've been seeing here.

I suppose there can be different varieties of mosses and alga that are adapted to various regions that react differently. If there are, I can't imagine what it takes for a roofing manufacturer to reach an acceptable balance.

Still convinced the stuff does damage roof covers.

Bill, for the record, I hate roof cleaning companies. If I were King of the Planet, the state would issue home inspectors seasonal hunting licenses and allow them to thin out the roof cleaner herd once a year. Every inspector would have a 2-kill limit. Inspectors would be lauded as heroes for doing a service to humanity. [:-devil]

ONE TEAM - ONE FIGHT!!!

Mike

Sorry, should have been more specific. - My neighbors roof is Asphalt Comp. I've seen it on several others also. I've been wanting to take a picture of my neighbor's roof but I don't know him, he might not take well to me pointing a camera at the back of his house from the the woods in back of mine... Thinking about it, the pic. I posted was pulled from Dan Freidmens web site, I don't even know where it was taken.

In regards to that and the Algae causing damage, I'm sure this is an instance where regional factors could easily have a dramatic effect...

We have pretty harsh Winters compared to you. Our full year cycle can see temperatures from 115 degrees to -20.

We don't have things like your wood destroying fungus' either.

Hell you have volcanic gases roaming around your area and coming down in the rain, that alone could account for a hell of a lot of things, including the lime being eaten away from the granule.

Out here, that algae is nothing but a stain.

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In regards to that and the Algae causing damage, I'm sure this is an instance where regional factors could easily have a dramatic effect...

We have pretty harsh Winters compared to you. Our full year cycle can see temperatures from 115 degrees to -20.

We don't have things like your wood destroying fungus' either.

Hell you have volcanic gases roaming around your area and coming down in the rain, that alone could account for a hell of a lot of things, including the lime being eaten away from the granule.

Out here, that algae is nothing but a stain.

Todays house, a Cape Cod, was oriented east west so the front surface of the roof gets sun all day long. The front slope is free of fungi and the back is all covered with a dark gray algae but no moss.

The difference in the conditions of the shingles was dramatic. On the front slope where the sun kills any alga spore, the roof is showing its age but the tab slots were consistent in width, the shingles lay flat and they actually look pretty good although it's definitely time to replace them. On the back slope, the shingles are literally shriveling up. the protective granule coating is sloughing off and the shingles are covered with random cracks. The only difference front to back is the alga.

The difference is so dramatic that the realtor thought I must be mistaken and began talking about how they'd have to see what an FHA appraiser says. I told him that they do not need to see what the FHA appraiser says because I'd just told him what the condition of the cover was - there isn't any if, ands or buts about it, the roof is completely shot and should have been replaced years ago. The client "got" it.

But it's just a little bit of algae!!

ONE TEAM - ONE FIGHT!!!

Mike

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In regards to that and the Algae causing damage, I'm sure this is an instance where regional factors could easily have a dramatic effect...

We have pretty harsh Winters compared to you. Our full year cycle can see temperatures from 115 degrees to -20.

We don't have things like your wood destroying fungus' either.

Hell you have volcanic gases roaming around your area and coming down in the rain, that alone could account for a hell of a lot of things, including the lime being eaten away from the granule.

Out here, that algae is nothing but a stain.

Todays house, a Cape Cod, was oriented east west so the front surface of the roof gets sun all day long. The front slope is free of fungi and the back is all covered with a dark gray algae but no moss.

The difference in the conditions of the shingles was dramatic. On the front slope where the sun kills any alga spore, the roof is showing its age but the tab slots were consistent in width, the shingles lay flat and they actually look pretty good although it's definitely time to replace them. On the back slope, the shingles are literally shriveling up. the protective granule coating is sloughing off and the shingles are covered with random cracks. The only difference front to back is the alga.

The difference is so dramatic that the realtor thought I must be mistaken and began talking about how they'd have to see what an FHA appraiser says. I told him that they do not need to see what the FHA appraiser says because I'd just told him what the condition of the cover was - there isn't any if, ands or buts about it, the roof is completely shot and should have been replaced years ago. The client "got" it.

But it's just a little bit of algae!!

ONE TEAM - ONE FIGHT!!!

Mike

Now given, again, that the algae your seeing may be a completely different animal then what I typically see it almost sounds like the algae may be just one more symptom of those harsher conditions and not the cause. I see the same thing, I'm sure we all do, where one side gets the sun, the other side doesn't and they age very differently. I see roof's all the time that are not bad on one side and shot on the other but the shot side doesn't necessarily have algae staining on it. If it did, again, I would add that to the list of symptoms caused by the exposure difference, not the cause of the severe difference in aging.

Now, for clarity, and I may just be interpreting what your saying differently, it sounds like what your talking about has some, physical dimension to it, almost like something you could scrape off a little and show it to someone in your hand? Here, I would call that mildew. What I'm talking about with algae staining is literally, just that, a stain, nothing I could possibly physically separate from the shingle.

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Nope,

It's a dark stain, you can't peel it off or scrape it off; about all you can do is treat it with a diluted bleach solution to lighten it. The weather pattern comes from the southwest here but the south side doesn't typically wear out first - the north side does.

Harsh weather? Not here. It only occasionally goes well below freezing in winter here and in summer it's pretty rare to see a day above 90°F - that's why folks were freaking out three weeks ago when it topped 100.

ONE TEAM - ONE FIGHT!!!

Mike

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About this gloeocapsa magma, does it begin to grow at a certain point and then spread?

I ask because I see these stains that begin at a point on the roof and then fan out on the downward side of the slope. Is it the water draining down that helps the bacteria spread that way?

I Can't speak to the why, but I recently had unwanted growth on my roof. After visiting one of the big box hardware stores I bought a concentrate that mixing with water and bleach. Spray it on, wait a couple mins, then hose it off. Works GREAT!!!

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  • 2 weeks later...
  • 1 year later...

I have a house that faces my yard, heavily wooded and the shingled roof looks like a green shag carpet with moss. All except the completely clear area directly under the skylight that is flashed with Copper, Clear and clean all the way to the gutters, probably around 12', hell the edges are even crisp like someone ran a lawnmower through it.

Comp or wood shingle?

Here I see that happening with shakes and wood shingle but not with comp. Here, it seems to work for 3 -4 feet and then peters out on a comp roof but will keep the roof clear to the eaves on shakes and wood shingles. I think it's got to do with absorbency; the wood cover absorbs the stuff leaching off the copper or zinc but the comp doesn't - at least not what I've been seeing here.

I suppose there can be different varieties of mosses and alga that are adapted to various regions that react differently. If there are, I can't imagine what it takes for a roofing manufacturer to reach an acceptable balance.

Still convinced the stuff does damage roof covers.

Bill, for the record, I hate roof cleaning companies. If I were King of the Planet, the state would issue home inspectors seasonal hunting licenses and allow them to thin out the roof cleaner herd once a year. Every inspector would have a 2-kill limit. Inspectors would be lauded as heroes for doing a service to humanity. [:-devil]

ONE TEAM - ONE FIGHT!!!

Mike

Bill;

I don't understand your hate for roof cleaners. What has any roof cleaner ever done to you for you to make the totally assinine and truly non-professional remarks that you made in this post. What puts home inspectors so far above roof cleaners that you think they should be granted the power and authority to "thin out the roof cleaning herd"? Is this just "ones man's biased opinion, or do you really have some kind of bone to pick with the roof cleaning industry?" Your comments could almost fall under "terroristic threatning" under the new laws. Perhaps you should give more "professional" thought to your comments before you make them. I really would like to know your "beef' with roof cleaners.

Care to explain?

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Bill;

I don't understand your hate for roof cleaners. What has any roof cleaner ever done to you for you to make the totally assinine and truly non-professional remarks that you made in this post. What puts home inspectors so far above roof cleaners that you think they should be granted the power and authority to "thin out the roof cleaning herd"? Is this just "ones man's biased opinion, or do you really have some kind of bone to pick with the roof cleaning industry?" Your comments could almost fall under "terroristic threatning" under the new laws. Perhaps you should give more "professional" thought to your comments before you make them. I really would like to know your "beef' with roof cleaners.

Care to explain?

The only thing I can explain is that you have a reading comprehension issue. Here's my only post on the topic:
"That's the same statement on literature from companies that sell all the crap to treat roofs that have black streaks. It also now appears on thousands of websites of roofing contractors, cleaning services and hundreds of home inspectors. Even homeowner associations are distributing this nonsense in bulletins.

Moss and lichens can damage a roof. What's causing the black streaks does not.

What's causing the dark stains is gloeocapsa magma. Everyone calls it algea, but it's really a species of cyanobacteria. It's a strain of photosynthesizing bacteria and it's "food" is water and the nutrients in rainwater, primarily nitrogen.

It's ugly, but it's NOT EATING THE SHINGLES!"

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Bill;

I don't understand your hate for roof cleaners. What has any roof cleaner ever done to you for you to make the totally assinine and truly non-professional remarks that you made in this post. What puts home inspectors so far above roof cleaners that you think they should be granted the power and authority to "thin out the roof cleaning herd"? Is this just "ones man's biased opinion, or do you really have some kind of bone to pick with the roof cleaning industry?" Your comments could almost fall under "terroristic threatning" under the new laws. Perhaps you should give more "professional" thought to your comments before you make them. I really would like to know your "beef' with roof cleaners.

Care to explain?

The only thing I can explain is that you have a reading comprehension issue. Here's my only post on the topic:
"That's the same statement on literature from companies that sell all the crap to treat roofs that have black streaks. It also now appears on thousands of websites of roofing contractors, cleaning services and hundreds of home inspectors. Even homeowner associations are distributing this nonsense in bulletins.

Moss and lichens can damage a roof. What's causing the black streaks does not.

What's causing the dark stains is gloeocapsa magma. Everyone calls it algea, but it's really a species of cyanobacteria. It's a strain of photosynthesizing bacteria and it's "food" is water and the nutrients in rainwater, primarily nitrogen.

It's ugly, but it's NOT EATING THE SHINGLES!"

Bill, I have to confess that I stole your language back when you wrote this, and now regularly spew it out as if I'm an expert on the stuff.

Sorry? Thank you? Insert whatever's appropriate, but no terroristic threatning (sic).

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