Staining Question

When you see Bleed Thru (staining) on an asphalt roof do you call it out as a serious defect ? Like I use Home Inspector Pro, would you put this in Red ? or simply as a normal comment something like:
There appears to be Bleed-thru of the shingles asphalt material resulting in black stains on the roof. This is normally caused by poor ventilation below the shingles. Recommend contacting a licensed roofing contractor to review repair options.


Hey James I can’t really help but can you post a photo because I’ve never seen this before. I’d like to know what you are talking about.

Sure Juan

Oooh. I thought you meant bleeding through the roof sheathing and visible from the attic. That looks like algae. How does it differ from bleed through. What is bleed through?

Edit. How can you differentiate algae from bleed through. That’s what I meant.

Hey James I googled it and this answers my question and yours

I’m agreeing with Juan looks like algae. Here is some text I snagged from the MB

One or more sections of the roof covering appear stained. An algae known as Gloeocapsa Magma is the most likely culprit and this algae affects nearly 80 percent of the homes across the United States. Gloeocapsa Magma is a species of algae that causes black streaking and discoloration on asphalt/fiberglass shingles. The black staining you see on many roofs is caused by the life cycle of algae and fungus spores that land on houses via wind or wildlife. While this algae can grow just about anywhere, it prefers humid environments. A preferred food source of this algae is limestone which is used as “filler material” by most shingle manufactures. Higher quality shingles are manufactured with preventative measures such as copper or zinc containing granules. Several methods exist to prevent and clean infected areas. Installing zinc or copper strips near the roof ridge can prevent further algae growth. Application of bleach (non-chlorine) can aid in removing the stains, as well as many available commercial cleaning products. Some products may harm vegetation beneath roof eaves or near downspout extensions. While many remedies can be performed by the home owner, we recommend the use of qualified professionals due to the extreme danger and risk of injury or death associated to roof repairs and cleaning.

Thanks Juan and Ken, I do know many of the causes, my question is do you call it out as a serious issue in Red ? or simply a general comment as to the condition?


Some insurnace companies will and have cancelled insurance polices because of dirty roofs.

Jim, I am a HIP user, and I use blue comments for the algae stains. I also include a link to show how it can be cleaned.

Black for me is description and general information.

Blue is use for maintenance items like the algae.

Red would be for repairs if there was moss that would require a lawn mower.:smiley:

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Thanks Dave, That is what I do as well, just wanted to see what others do.


Jericho Park Rd??

HAHA…you got it :cool: Working on the report, as I did the inspection yesterday and was curious after all these years what others do with a similar finding.


My master file -

Report Informational: 95% of common black stains on roof coverings is the Gloeocapsa magma algae that grows and feeds on the minerals in the shingle. This biological attack from algae can exacerbate damage to shingles and accelerate the demise of an asphalt roof leading to earlier than necessary roof replacement. Algae and most other forms of fungi reproduce from tiny airborne spores. Like most plants, these spores will grow wherever they find minerals, moisture, warmth and light. The algae takes root on the surface of shingles helping to dislodge the protective granules. Surface temperatures are also increased because of the dark stains. Its growth holds water on the roof’s surface which intensifies the sun’s ultra violet rays like a magnifying glass. The increased moisture and UV rays work to further dislodge the protective granules and attack the shingle’s protective asphalt coating. Heat, moisture, UV rays, and thermal movement from temperature extremes are a roof’s greatest enemies. These are intensified by algae growth. Studies suggest that algae stained areas, versus unstained areas on the same roof, reveal that surface temperatures are increased by as much as 10% which can increase cooling costs. Products are generally available to clean roofs of this algae stain and minimize its growth on a periodic basis.

FYI - Oxiclean works. Clean my roof and sisters like new. (I’ve always heard to not use bleach but no one has told me where that information comes from). I now wash my roof every 3 years (Gulf Coast chemical plants and trees) even though it does not show a lot of visible mold. Let the chemical do the work. I rinse with pressure washer @ (low pressure). Does not affect roof granules as indicated by the black water discharge from the downspouts. Roof looks clean but rinse water shows otherwise. I have a less than 6/12 pitch roof and has had no “slip” problems with a wet roof. I assume on higher pitched roofs the Cougar Paw shoes may offer some safety.

Great work Juan:-)
A follow up on how to remove staining and why the staining was created would be an idea.

As for pressure washers. Even at a low rate of pressure you are degrading the the top layers and possibly hastening the delamination of 2 things, The top coating that protects from UV for one and unsealing the shingles.

Tree’s & atmospheric conditions most likely the culprit.

Now James Write up your report with what you observed and from where.
Ground, Ladder that the eave.
Report on condition. No speculation of what may occur.
Home inspections are the visible condition of the components on “the day of the inspection.”
IE: A home owners buyers the home and places on a new roof on the unit because they want to, not need to or have to, have piece of mind for 20 tears.

A report may read as follows: The 12/12 pitch roof architectural shingles appeared to be in good condition.
SUSPECT: 2 deficiencies;
#1 Valley are closed. A shingle valley is recommended to be open.
A parallel line is marked 2" off center of the valley from the bottom to the peak of the roofs deck… The excess asphalt shingle is cut away exposing the metal under the shingles. This exposed metal allows debris form tress such as leaves, seed pods, small pieces of wood, ice and snow to be removed more readily by atmospheric conditions IE: Wind and rain.
#2 Algie staining on the front left hand gable.
Algie staining can be removed without harm to the asphalt shingles. There are several methods used to remove the algae.
Add a link. Bob’s your uncle mate :slight_smile:

If you know the shingle manufacture do a class action search. Nathan has a service I recommend to all HI’S. RECALL CHECK.

I recommend that pressure washing is avoided at all costs. I have an commercial pressure washer. I can reduce the pressure to 150 LB. SQ.IN.
I have the basic principles of proper application and maintenance for sloped and flat roofing. I have my roofing trades licence.
I personally would never pressure wash a shingle roof let alone other components of a building unless you know what you are doing.

Just about see it every other roof here in the lower south !

All the algae growth I have seen has not been streaked like that, has run straight down the roof, and has been more uniform.
The rea telltale for algae is to look below areas with flashing. You’ll see where runoff carrying chemicals absorbed from zinc have reduced growth.

Also, algae is caused by retained moisture, not poor ventilation. Poor ventilation would cause a warmer roof and faster evaporation, meaning less moisture on the roof and less algae.

That looks like areas of concentrated failure that are producing asphalt-related staining that is gradually dispersed as runoff spreads as it runs down the roof. The diagonal pattern appears to follow the shingle installation pattern, and the fact that its not uniform indicates that it’s a batch problem… that is, the shingles on the roof are from different batches and the bundles got mixed as they were loaded, so that failure occurs unevenly across the roof. I think it’s a batch of poor-quality shingles mixed with a better batch.
Of course I’ve never inspected in Maryland.

  1. How was the rest of the roof, was it just this slope?
  2. Was there evidence of this condition being affected by galvanized flashing?
  3. Could the diagonal pattern be caused by the direction of prevailing winds?

This looks like premature failure to me. I’d put it in the summary. If I were a buyer, I’d be asking for a drop in price.

Kenton, I sniped the image and unfortunately it not high resolution.
I see architectural asphalt shingles on a 12/12 or greater.
As for the hypotheses
“That looks like areas of concentrated failure that are producing asphalt-related staining that is gradually dispersed as runoff spreads as it runs down the roof.”
I agree somewhat with the theory but it is a steep grade.
Let us look at the theory of algae growth moving up as opposed to bitumen chemical staining being carried down. ALGEA.
Here are 2 photos of algae. both from credible sites.
I see a tree in close proximity to the eave and about 20+ inches above a gutter. That gutter will allow build up.
Moss has started to grow as in illustration one from inspectapedia.

The shingle degrading theory although feasible does not carry all the characteristics I would need to be 100% sure of a hypotheses to be developed. It is in on the lower quadrant of the shingled roof deck.