Thread: Any opinions on if this causes damage to the roof? See photo

I have seen these stains numerous times on composition roofs, as have many home inspectors (See photos). From what I know and read, it is algae that it is a parasitic on the shingle, ingesting some mineral that is in the granules (Limestone?). Any of you call this out as defective or just mention it and move on? From your perspective, is this something you write up as a defect? (I never have before). Just wondering what others think.

Thanks

Gene

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Gene any information form the attic under these areas ?

I do see water stains form the gutter ending on that one are of the roof looks just like your other photo.

I would call it out as an indication of an unknown moisture condition as I may not have enough information what is going on under the shingles.

Most of the time i find i see stuff like i find rust condition on the nails in the attic...

Did you see any rust on the nails in the attic ?

Best

Ron

Gene,

Are you sure thats not "Oak wilt" or what some call "Oak Blight"? It is a virus which attacks trees and it can leave staining as such on roofs.

rick

To me it looks like a stain coming from a point on the shingles.
I don't usually see fungus stains that dark, much less on a dark roof.

Geez, every other house around here has black streaks on the shingles...covering the entire roof not just in one little spot.

Roofs in the sun, shade, covered with trees, not a tree within half a mile, all conditions. Nope, don't call it out.

There was a debate that if the algea, fungus, XXX is eating the limestone in the granules, then the roof shingles are damaged/deteriorated because there is less limestone than the manufacturer put there. Does it shorten the life span of the shingle from a function perspective? Not that I heard. Ugly, yes. Function issue, no.

", every other house around here has black streaks on the shingles...covering the entire roof not just in one little spot."


Thats what usually see, and also why I think it may be something in the shingles causing the stain.

Looks like black algae. North side of the roof no doubt. Rarely a cause for concen.

Actually I did not mention that these photos were from two houses, side by side neighbors and both houses had stains only on the north sides. Neither of these houses were shaded by large trees. There were trees nearby but no trees with sap dripping. I was only at the house a short while today when I took these photos and will be back tomorrow to check the attic but I suspect it is the fungus that is on the shingles. I see it sometimes in neighborhoods around Dallas, in neighborhoods in full sun with no big trees around. I do think it is "treat related" since a lot of the observed houses did not have a lot of trees around (even though in one of two photos there are trees). Anyway, my 2 cents worth. Thanks all for your comments.

Gene

Sorry, I meant to say I DO NOT THINK it is tree related. Excuse the typo.

One more opinion.
It's algae. The point sources at the top of each stain are probably bird dropping sites, which will provide sufficient nitrogen for the algae even when the stuff is 90% washed away. Doesn't hurt the roof, or the sheathing, just the appearance.
DetroitMatt

GS,

Did you see this thread on similar "concern"?

http://www.inspectionnews.net/home_i...alt-roofs.html

The blue-green (looks black on death) algae is named in the thread also links on extractive bleeding (doesn't appear to be the case in your photos).

"Did you see this thread on similar "concern"?
http://www.inspectionnews.net/home_i...alt-roofs.html
The blue-green (looks black on death) algae is named in the thread also links on extractive bleeding (doesn't appear to be the case in your photos)."

Watson
Good information, but it looks just like extractive staining to me, not algae growth.


Algae on roofs: Black or Green Algae stains on roof shingles: Causes, Cure, Prevention of Algae, Moss, Lichens, or Black Fungal Growth on Roof Shingles
Black algae stains on asphalt shingles tend to be fairly uniform over the stained area, appearing more on shaded and more damp roof slopes. When stains on the roof surface are more uniform in pattern and when they cover a wider area that does not originate at one or more single pinpoints in the shingles, this may be a black algae growing on the shingle surface.

Extractive bleeding shingle stains: Cause & Diagnosis of Extractive Bleeding - Black Stains on Asphalt Roof Shingles
Readers will notice that the pattern of stains we ascribe to algal growth (and include in roof photographs) do not appear as originating at a point. Where we find algae stains on roofs it appears in wider areas, it does not originate in an inverted vee point

Extractive bleeding or "bleed through" stains leaving black streaks running down an asphalt shingle roof is an indication of a defective roofing product. The chemistry of the shingle is permitting black pigment from the asphalt to leach to the shingle surface and run down the roof. Typically bleed-through on asphalt shingles appears as black streaks running down shingles.

That is why the roof cleaning business is booming in KY. There is a lead strip available to be installed at the ridge to prevent this from happening. It must work because with a roof full of stains the only clear spout is downside of the lead based vents.

Since the algae thing was answered I just wondered if A) the super duper high chase was on the house you inspected?.. and.. B) did you push on it to see if adequately supported??.. just wondering as these are often poorly built and will actually move when you push on them.

Most of the time the stain starts at the gutter line which would make you think the gutter holding water is contributing to the problem, but next door the stain starts at the ridge. Yes, it seems to be NSEW shade or no shade. You can spend extra money to get a fungicide in the shingles which makes it resistant, but then it gives up and stains.

" There is a lead strip available to be installed at the ridge to prevent this from happening. It must work because with a roof full of stains the only clear spout is downside of the lead based vents."

I think you are refering to "Zinc", not "Lead"

Yes Zinc, but I have been told that lead and copper willl do the same job.

Originally Posted by Rick Cantrell

"
Watson
Good information, but it looks just like extractive staining to me, not algae growth.


Algae on roofs: Black or Green Algae stains on roof shingles: Causes, Cure, Prevention of Algae, Moss, Lichens, or Black Fungal Growth on Roof Shingles
Black algae stains on asphalt shingles tend to be fairly uniform over the stained area, appearing more on shaded and more damp roof slopes. When stains on the roof surface are more uniform in pattern and when they cover a wider area that does not originate at one or more single pinpoints in the shingles, this may be a black algae growing on the shingle surface.

Extractive bleeding shingle stains: Cause & Diagnosis of Extractive Bleeding - Black Stains on Asphalt Roof Shingles
Readers will notice that the pattern of stains we ascribe to algal growth (and include in roof photographs) do not appear as originating at a point. Where we find algae stains on roofs it appears in wider areas, it does not originate in an inverted vee point

I disagree, looks to be characteristic, including the description and location, and obvious complicated roof type, pitch, drainage paths, and ventilation challenges. Buildup from below, as most colony type debris accumulations.

Simply put, does not appear to be extractive bleed, and despite inspectapedia author's (DF) characterization, appears as usual and often seen accumulations. Modern compo and arch roofing, see discoloration just not as intense (accumulation) in other areas also characteristic as is discoloration areas below.

Products of extractive bleeding do not "bleach" fade neither would soot staining from downdraft (although TSP or other surfactant, and lye residue from household bleach solution could work to somewhat lift and float off, i.e. high chimney above to the south and slightly west). Simple to determine with "oxygen bleach", household bleach solution, and hydrogen peroxide test areas, closeup view, and/or a microscopic examination of test sample.

Shingle age is important in factor on the bleed out issue. Normally nwer shingle have a potential to "tobacco stain" as the water borne oils left over on the shingle surface from the manufacture will runn and create a brown line down the face. Usually this will wash off over time and be less visible. it is officially not a defect as it is just a small patch of oil dripping and the shingle function remains the same.
The algae possibility is well cover in earlier threads. I would wonder why only in small spots or lines if it was algae, the bird dropping theory is an interesting idea.
Another not mentioned is non galvanized nails used for roof jacks that are rusting out and that is in fact black rust from common nails. In the attic you may find long 16 d common nails poking though the attic boards where the roof jacks were placed to work on the roof. The roofers dont use galv nails for safety jacks as they are weak and no one is normally looking for galv for the jack nails. It is difficult to remove these once the roof is in place and they are just pounded flat after the jack is removed.
In a humid climate they are still exposed to moisture and will rust out and turn black.
I bet it is the nails.

Originally Posted by Mark Webb

Shingle age is important in factor on the bleed out issue. Normally nwer shingle have a potential to "tobacco stain" as the water borne oils left over on the shingle surface from the manufacture will runn and create a brown line down the face. Usually this will wash off over time and be less visible. it is officially not a defect as it is just a small patch of oil dripping and the shingle function remains the same.
The algae possibility is well cover in earlier threads. I would wonder why only in small spots or lines if it was algae, the bird dropping theory is an interesting idea.
Another not mentioned is non galvanized nails used for roof jacks that are rusting out and that is in fact black rust from common nails. In the attic you may find long 16 d common nails poking though the attic boards where the roof jacks were placed to work on the roof. The roofers dont use galv nails for safety jacks as they are weak and no one is normally looking for galv for the jack nails. It is difficult to remove these once the roof is in place and they are just pounded flat after the jack is removed.
In a humid climate they are still exposed to moisture and will rust out and turn black.
I bet it is the nails.

Look at the bay window pic. I don't think a roofer installed a single roof jack in that area to stand on. It's only on the north side also. If nails were the cause it would be on all sides.

Originally Posted by Matt Bezanson

One more opinion.
It's algae. The point sources at the top of each stain are probably bird dropping sites, which will provide sufficient nitrogen for the algae even when the stuff is 90% washed away. Doesn't hurt the roof, or the sheathing, just the appearance.
DetroitMatt

This is what you are seeing and how to rid the roof of it.
FYI;

]
There is a lot of misconception when it comes to unsightly black streaks on asphalt shingles. Perhaps you have seen such black streaks on roofs, they normally first start to appear on the north facing slopes of the roof. The north side is the side with the prevailing amount of shade and moisture. Once the algae lands on the roof it does not go away or ever get any better. It will begin to feed on the shingles and will spread over time eventually taking over the entire roof. Roof cleaning is a great service to help with this problem of roof algae. When done right, roof cleaning will restore the roof’s appearance, increase curb appeal and value, and will stop the damaging effects of the roof algae. The proper method is a low pressure chemical application which is recommended by the major shingle manufacturers. A pressure washer should not be used because the excessive pressure will damage the shingles. They also recommend a bleach based cleaner, it is safe to use on the shingles and it will kill and remove the algae properly. No other chemical should be used, only bleach according to the shingle manufacturers such as Owens Corning.
Not taking care of roof algae can lead to increased home and cooling costs and will deteriorate the shingles. Roof algae will definitely lessen the longevity of your shingles because it does not allow the shingles to reflect heat like they need to. Years of life can be shaved off the roof when roof algae is left untreated. It is like anything else that is exposed to the elements. For example, if vinyl siding is neglected it can also accumulate mold, mildew, and algae and if left untreated it will lessen the longevity of the siding. Roof’s are the same and when they get dirty or get infected by roof algae, they just need cleaned. It is not rocket science but I am amazed at the amount of homeowners and even roofing contractors that are not aware of what roof algae appearing as black streak are.
I have heard all kinds of explanations of what these unsightly black streaks are. I’ve heard it said they are water marks, nail rust, the tar paper showing through, and even tree sap. None of these are true, it is an airborne algae technically called Gloeocapsa Magma. It gets on the roof, survives by feeding on nutrients in the shingles, and is spread down the roof by rain creating the black streaks. It is no different than mold on vinyl siding, or mildew on a wooden deck it can be cleaned like anything else. And like noted, the proper roof cleaners and cleaning methods are recommended by the major shingle manufacturers whom recognize roof algae as an ongoing problem. Educate your family, friends, and neighbors as to what this airborne algae is because it can jump from roof to roof. This is why you’ll see many roof’s affected in an area and none affected in other areas. In the south your the climate is more prone to grow algae and mold, roof’s are cleaned almost yearly. In the more northern states the algae is a problem but once a roof is cleaned properly it will stay clean for a minimum of several years. But because roof cleaning is not as popular in the northern states it seems that not many people know that it even exists nor what those black streaks on roofs are. Help spread the truth about black roof algae streaks and roof cleaning.

It will begin to feed on the shingles and will spread over time eventually taking over the entire roof. Roof cleaning is a great service to help with this problem of roof algae. When done right, roof cleaning will restore the roof’s appearance, increase curb appeal and value, and will stop the damaging effects of the roof algae

I don't believe that the algae FEEDS on the shingles. It is feeding off of the grime that accumulates on the roof. Do you have a source for your opinion Gary?

Call me ignorant, but I haven't seen a credible source stating that algae will damage the roof. I would like to see/ read any info. you can provide that states this to be the case.

Originally Posted by Brandon Whitmore

I don't believe that the algae FEEDS on the shingles. It is feeding off of the grime that accumulates on the roof. Do you have a source for your opinion Gary?

Call me ignorant, but I haven't seen a credible source stating that algae will damage the roof. I would like to see/ read any info. you can provide that states this to be the case.

Is this a qualified opinion? Simply do a google search and you will find hundreds of like opinions. That is also why the stuff grows on the drive & walk ways. Even if the damage is slight, the appearence is unsightly. It loves and thrives on limestone. Go to my website. There is a ton of info there. Home
Gary
Mastering Roof Inspections: Asphalt Composition Shingles, Part 42 - InterNACHI (opinion)

B.W.,

No, Gloeocapsa isn't actually still classified as an algae, although its still called "blue-green algae" my many. Its actually considered to be bacteria, of the cyanbacteria type. Cyanbacteria can "Feed" from the air, light and moisture, photosynthesizes and perform nitrogen fixation. Protected by encapsulation method in dry periods, and bound together and to host roof by a bioslime.

Gloeocapsa is a unicellular cynobacteria. The gelatinous material (bioslime)surrounding each cell causes the cells to stick together (and to other things, such as the roofing surface). Like plants, cynobacteria can have the photosynthetic pigment chlorophyll A and they use water as an electron donor during photosynthesis. When water molecules are split, oxygen is liberated.

Catching Fungi spores, which can feed off it, and other "nutrient rich goodies" caught in/on the bioslime layer, and prematurely break down the asphalt.

Moisture rich environ of the slime - the discoloration nulling the granules' ability to deflect UV, sometimes daily near "boiling off" temperatures the moisture at the edge of the slime layer, holding moisture within the shingle environment, and the asphalt further becomes exposed to air, UV, and greater temperatures than otherwise, the moisture if freezing can pop off granules, and the premature weathering of the asphalt - the granuals are lost prematurely, thus a premature rapid aging of the roof. Hosting Lichen (bacteria plus fungi), enjoying the moisture rich, now nutrient rich environment further deteriorating shingle surface, etc.

Seems to me I recently read about a similar, same family (OS20?) from Antartic? colony hosted on a piece of cliff rock from U.K. taken to the International Space Station and placed outside the station in orbit. IIRC it was exposed to UV, the boil-off of space vacuum for many months (at least five I belive) and later collected and returned to earth for examination. Apparently it survived quite well. (I think I was reading about this sometime last August or so, an extended exposure experiment on the International Space Station, after a few years earlier shorter exposure on the line of several days in near space, this time many months), thus producing some discussions regarding terraforming with cynobacteria. Anyway that's the way I remember it.

Anyway, regarding weathering of roofing materials, I think you might find the following article informative. It will start to get interesting on the subject around part six, but suffer through if you can from the beginning. The references, several of which I think you'll also find very enlightening, should be available via your local library reference desk, if not freely available on the www.

Here is the title, authors, publication date, a (clickable) link to view same, and the abstract:

From: Weathering of Roofing Materials - An Overview
Paul Berdahl, Hashem Akbari, and Ronnen Levinson
Lawrence Berkeley National Laboratory Berkeley, CA 94720
and
William A. Miller
Oak Ridge Naitonal Laboratory
Oak Ridge, TN 37831.
Published June 11, 2008
See (clickable link eScholarship: Weathering of Roofing Materials-An Overview
Abstract:
"An overview of several aspects of the weathering of roofing materials is presented. Degradation of materials initiated by ultraviolet radiation is discussed for plastics used in roofing, as well as wood and asphalt. Elevated temperatures accelerate many deleterious chemical reactions and hasten diffusion of material components. Effects of moisture include decay of wood, acceleration of corrosion of metals, staining of vlay, and freeze-thaw damage. Soiling of roofing materials causes objectional stains and reduces the solar reflectance of reflective materials. (Soiling of non-reflective materials can also increase solar reflectance.) Soiling can be attributed to biological growth (e.g. cyanbacteria, fungi, algae), deposits of organic and mineral particles, and to the accumulation of flyash, hydrocarbons and soot from combustion."

A few selected paragraphs below:

"As far as biological growth on roofing surfaces is concerned, it is clear that a large variety of species is expected to be present. For example, some of the species of fungi that occur in soil may be expected to be present. However, the ultraviolet radiation incident on roofing can kill many organisms. We have noted earlier that the cyanobacteria Gloeocapsa infests mineral roofing granuels, leading to black colored stains. In a study of biomass accumulation on single ply roofing membranes exposed in Oak Ridge, Tennessee [44], it was found by phospholipid fatty acid analysis that the biological growth was in this case primarily fungal in nature.

C.C. and P.M. Gaylarde [45] recently published a study of 230 biofilms found on the exterior of buildings in Europe and in Latin America. They classified the biofilms according to the predominant microscopic organisms found, of which the most important were various cynobacteria, algae, and fungi. The substrate was important with, for example, fungi rarely found on mineral substrates and often on paint. Climate was believed to be important as well, with algae more prevalent at cool damp European sites and dark-colored cynobacteria frequently found in tropical locations at elevations above 1000 m."

"In the roofing industry it is often not known exactly what species make up the biomass deposits on roofing. In fact, the terms algae and fungi are somtimes used interchangeably. However, it is well known that in humid climates, such as the southeastern United States, the growth of biomass on roofing leads to visible stains. In some cases, it has been noted that staining does not occur near copper and galvanized (zinc) flashings. In a patent by Narayan et al., [49] reviewing prior art, it is noted that algae growth on asphalt shingles can be inhibited by metal An particles, ZnO, ZnS, and cuprous oxide Cu2O). Thus it appears that zinc and copper ions can inhibit biological growth. A more recent patent [50] likewise discloses that Cu2O, either alone or with zinc compounds, is effective in roof granules, to prevent growth of cyanobacteria (such as Gloeocapsa) and also fungi."

[44] W.A. Miller, M.D. Cheng, S. Pfiffner, and N. Byars, The field performance of high-reflectance single-ply membranes exposed to three years of weathering in various U.S. climates, Oak Ridge National Laboratory report prepared for, and available from, the Single-Ply Roofing Institute, Needham, MA (2002).
[45] C.C. Gaylarde and P.M. Gaylarde, A comparative study of the major microbial biomass of biofilms on exteriors of buildings in Europe and Latin America, Int. Biodeterioration & Biodegradation 55, 131-139 (2005).
[46] P. Dupuy, G. Trotet and F. Grossin, Protection des monuments contre les cyanophycees en milieu abrite et humide, in R. Rossi-Manaressi (Ed.), The Conservation of Stone I, Centro per la Conservazione delle Sculture all'Aperto, Bologna, 205-219 (1976).
[47] J.J. Ortega-Calvo, X. Arilio, M. Hernandez-Marineb, and C. Saiz-Jimenez, Factors affecting the weathering and colonization of monuments by phototrophic microorganisms, Science of the Total Environment 167, 329-341 (1995).

[49] S.B. Narayan et al., Method of inhibiting algae growth on asphalt shingles, U.S. Patent No. 5,356,664 (1994).
[50] I.B. Joedicke, U.S. Patent Application 2004110639 A1 (June 10, 2004).

HTH,

H.G.

A good way to get rid of any moss, vegetation etc, from what I have researched, is to use shingles that have copper granuals embedded in them. A copper ridge vent, copper flashing, etc. Same goes with tree roots. IMO

I've seen zinc strips installed on both sides of the ridge but they didn't really seem to do anything to deter algae and moss growth.

Is this a qualified opinion? Simply do a google search and you will find hundreds of like opinions. That is also why the stuff grows on the drive & walk ways. Even if the damage is slight, the appearence is unsightly. It loves and thrives on limestone. Go to my website. There is a ton of info there. Home
Gary

There is disagreement throughout the roofing industry as to whether algae is anything but a cosmetic issue. I've looked into this in the past, and pay attention to the condition of shingles when performing a home inspection. In the 10 years I've been doing this , the only thing that I believe may occur is that this algae may loosen up the seal tabs on 3 tab shingles. In my area, I've never seen it actually eat away/ damage a shingle. What I have seen is roof cleaning companies cause major damage to roofs. I'm sure that as with any profession there are good and bad roof cleaners, but in my experience, it's safer to leave the algae in place rather than clean it. Opinions will vary of course.

This is straight from your website you posted as your credible source:
"Algae attaches itself to the shingle by secreting a substance that bonds it tightly to the surface. Growth can be difficult to remove without damaging the roof. The best method is prevention. Algae stains can sometimes be lightened in color by using special cleaners. "


So when you do a roof cleaning, are you actually removing the algae, or are you just lightening it? If you are just lightening it, then are you in any way actually protecting the roof covering?

BTW: This is just a debate and questions for me to form a better opinion/ learn. I need to look into the chemicals used to clean a roof so I can become better informed. I didn't see any of the info. on your website as to what chemicals you are using. Is it some sort of TSP/ TSP substitute mixed with bleach?
In your area, how long does it take for algae stains to show up on a new roof covering?


HG: Thanks for posting that useful information. Do you agree with everything that Gary posted in his initial post, and do you think frequent roof cleaning is a good idea.

Say algae does in fact cause premature failure of a shingle, and a 30 year shingle will last 2 years less due to algae growth. A typical roof covering replacement in my area will cost 8k (random figure). That means that the value of that roof covering for that house with the 8k roof is $267.00 per year for the 30 year period. . By not cleaning the roof, you are losing a little over $500.00 value in the roof covering. Let's say a roof cleaning co. needs to clean that roof more than 1 time during that 30 year period. Based on Gary's website, a roof cleaning costs from $300- $500 per cleaning. If a roof needs to be cleaned more than one time, wouldn't you hit a point of diminishing return? Of course the above scenario is extremely simplified and I left out a bunch of factors......


This from CASMA (from back in 1997- I wonder what their current stand is?): http://www.inspectorsjournal.com/for...ng%20Algae.pdf

B.W.,

You're welcome.

Originally Posted by Brandon Whitmore

... Do you agree with everything that Gary posted in his initial post?

No, I thought I made that clear when I presented contrary information regarding distinctions and differences; and not only refered to credible source articles/publications/studies but quoted some.

B.W.,

It appears you have chosen to completely re-write your prior post after I had begun the process of responding to it.

I note you are still generalizing and referring to algae. It seems you have not followed-along on what I posted previously, or reviewed the linked article, or reviewed some of the highlighted reference articles.

Therefore, and in the form of the now-edited version of your follow-up question(s) to me, and apparently to all, I cannot answer - as to the FORM of the question(s) posed. Perhaps if you re-phrased as I dispute the "givens" or the presumptions you've made therein (and the obvious conflicts with the information I previously presented for your review).

Brandon!

That's now the fourth edit since I first responded to your post! I cannot keep up.

It would be easier if you made a new post after yours is first responded to, then to keep re-writing it or adding on.

I provided much more current information regarding biomass formations on roof coverings. Please review the earlier linked (and a few selected quotions, including its abstract and a few citation references). Note G.Magnum is not an algae.

No, I thought I made that clear when I presented contrary information regarding distinctions and differences; and not only refered to credible source articles/publications/studies but quoted some.

I will definitely review the info. you have provided, as soon as I can.

In regards to the editing.... I was/ am dealing with a 15 month old son so I am unable to spend a lot of time on my posts, and I definitely can't concentrate fully.

That's now the fourth edit since I first responded to your post! I cannot keep up.

Just trying to keep you on your toes. Between my kid running around, jumping on me and the 'puter, hitting the keys while trying to make an escape at the same time, screaming, etc., I can't focus too well. The water is fenced off 'til I get some alone time.

Please review the earlier linked (and a few selected quotions, including its abstract and a few citation references). Note G.Magnum is not an algae.

Will do, as soon as I am done playing Mr. mom.


Don't take any offense, but the way in which you write things, I have trouble following along at times. Consider it crappy reading comprehension on my part. I often have to sit down somewhere quiet and really focus to fully grasp what was written.

Have a good evening. I promise not to edit this post, unless it is just for a spelling or grammar issue.

Here's an example of algae stains and a bit of moss, too, 1972 house with 15 yr old fiberglass reinforced shingle roof. This side faces north.

I'd say the zinc strip is all washed out, eh?
I drive past this roof sometimes and it is noticeably greener now.

The reason for the copper or zinc strips is that acid rain will react with the metal creating Zinc or Copper Sulfate which is a algae inhibitor. Copper sulfate is used in fountains, fish tanks and water attractions to kill algae and keep the water clear. In higher concentrations it will actually turn the water a blue/green.

Hello,
We are a retiring roofing co. in Mich. and will be opening a Fl. roof cleaning business. I have done extensive research on this very topic and have found personally it does cause loss of granules. I have searched for science to support the theory of what we have been seeing a lot of lately in the north.here are some images for you to draw your own conclusion.These were taken from a roof that was 10 years old. The link is to my web site so you will be able to see them in large images. If I posted them here it would stretch the forum to much.
Roof Cleaning Bradenton Florida 941-822-2454

I have found the articles from the Berkley Institute as well as a few others. I support science such as this, as opinions can be self-serving sometimes.
We as a roof replacement company for over 28 yrs have never seen such a change in the Cyanobacteria migrating north as we have in the last 2-3 years. Research on this has been minimal and further studies in regards to allergy's and damage to roof systems as well as penetration into the interior of the home hopefully will be conducted more in the near future.
For now the best case is removing this off the roof as unless tested by a lab,only a generalized assumption can be given.
Non-pressure roof cleaning does remove the algae, the chems kill it not just whiten it. That would be Lichens, I have personally tested this and the Lichen turns white then back to green then dies. Nature takes care of the rest.

Here is an article on Lichens and the symbiotic relationship the have with cyanobacteria and fungus.
http://www.tnenvis.nic.in/Lichens/LichenFAQ.pdf

"FACTS ABOUT CYANOBACTERIA AND CYANOBACTERIAL HARMFUL ALGAL BLOOMS — Newsletter Fall 2009"
Cyanobacteria HAB bloom's

Microbes And The Dust They Ride In On Pose Potential Health Risks
Microbes and The Dust they ride in on.

These are just a few I have on file.
Hope this helps to understand some science into the black streaks on the roofs,grounds and buildings exteriors.
If you would like more info we have a ton over at the forum we belong to and is a great group of guys and some gals, that would be more than happy to answer any questions you might have.
Roof Cleaning Institute Of America
We have about 1600 + members from all over the US and some from other country's as well.
I hope this helps answer some of the questions your members may have. I look forward to reading and learning from your forum at an inspectors point of view as well.
Take Care
Kim R

Hi. from my perspective the stains do look like alage although the stains are in a rather unique pattern. This typicaly is not an issue with roof material function but one of cosmetics. On this higher end home I would at least mention its presence and look for any water stains and try to put a moisture meter under the area. I have seen these many times and have not had issue with just mentioning them in the reporting.

Essex County New Jersey Home Inspectors

Home inspections in Essex County New Jersey

This is a fungi staining. Real common in NW. Mostly will be noted on north side of structure and as well as shaded areas of the roof system. I always call for a treatment. Next step is moss. Clean and treat properly and under no circumstances pressure washing. Multiple companies out here offer pressure washing of comp roofing, however I do not feel that is good for the system. Granular content on these roof systems is designed for curb appeal, but also to help limit the UV damage.

Originally Posted by Jim Scott

This is a fungi staining. Real common in NW. Mostly will be noted on north side of structure and as well as shaded areas of the roof system. I always call for a treatment. Next step is moss. Clean and treat properly and under no circumstances pressure washing. Multiple companies out here offer pressure washing of comp roofing, however I do not feel that is good for the system. Granular content on these roof systems is designed for curb appeal, but also to help limit the UV damage.

Using a pressure washer on asphalt shingles may void the warranty. The practice of pressure washing goes against the ARMA guidelines.

http://www.asphaltroofing.org/pdf/tb_217.pdf

Kim R

Gene, We see this staining all over the Houston area. Unless the extra money was spent on an algae resistant shingle. You will also notice that on roofs where galvanized vents, tc. are located the area immediately below the zinc is completely clean, even if all of the remainder of the roof is black. Zinc Oxide kills the algae. From everything I have read, this stuff is caused by airborne fungi that land on the roof and does not cause a shortening of the lifespan of the roof. Therefore, in my opinion, I certainly wouldn't call it a defect. Take a look at the following excerpt from the InspectA Pedia Website: Algae on roofs: Black or Green Algae stains on roof shingles: Causes, Cure, Prevention of Algae, Moss, Lichens, or Black Fungal Growth on Roof Shingles
Does Roof Algae Growth on Asphalt Shingles Affect Shingle Life?

Comments & Opinion on three claims of harm caused by roof algae:
1. Roof algae causes shingle granule loss? We have read in roof-cleaning-product sales literature that black algae reduces roof shingle life by "eating" at the shingles (loosening mineral granules and exposing the shingle substrate). We agree that granule loss is associated with reduction in shingle life, but inspecting black algae-stained roofs in the U.S. we have not seen a difference in granule loss between the black algae-stained area and the non-stained areas. Contact us if you have different experience.
2. Roof algae causes shingle tab lifting? We have also read in roof cleaning product sales literature that black algae on roof shingles is a cause of shingle tab lifting. We have not observed this phenomenon nor have we found technical reports of this defect nor an explanation of its causal mechanism.
3. Roof algae releases harmful toxic spores on, around, and into homes? This is nonsense. Except when the ground is covered by snow, outdoor air has varying amounts, often very large amounts of all kinds of particles, including mold spores and rarely, algal spores. Outdoor airborne particles indeed can enter a home through open windows and doors, and if building occupants are allergic to specific particles (typically certain pollen grains, some molds, other dust particles) they may suffer. Having inspected and tested airborne particles in and around nearly 3000 buildings we have never once found a significant level of algal particles in indoor air.
OPINION: As we said about green algae on roofs, the presence of these black "fungal" or algal stains on the roof is sometimes an indicator that this roof area is in a shaded spot (look for shade from trees or nearby buildings) where you may want to be alert for development of moss or other roof problems, but the level of damage from the black algae is probably low, even less than that caused by lichens and certainly less than that caused by moss.

The mineral coat on asphaltic comp roofs seems to be a "hotbed" for biological growth (like mildew etc.). Not a real problem just doesn't look good.
I see this all the time, also showing up on the light colored comp roofing. Better quality comp roofing comes new with anti-fungle treatment that they say should last 3 to 5 years, some they claim the first 10. Mention in your report the discoloration and, if concerned about the appearance, might recommend a reputable home maintenance or preservation specialist to consult on treatment.