What I'm Seeing Now

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Black Algae

Prevalent in Northern Virginia, and to the south, is a roof staining problem called "black algae."  It looks like a dripping, running black stain, usually on a shaded roof, or on the side facing away from direct sunlight.  Incorrectly called mildew and fungus, the staining is an algae, typically Gloeocapsa magma.  I see it all the time.

The black algae is usually distinguished as a general stain. 

It runs down the roof as it is carried by water.

It grows where it obtains food in the roofing materials.

I do not know how prevalent it is around the country, but suspect it is common.

Algaes can grow on all types of roof surfaces - I have seen it growing on asphalt shingles, clay, concrete asbestos and even slate.

It seems to me that it has become more common in the last 15 years or so.  One theory as to why is that manufacturers began then to change the composition of shingles, adding more limestone to lend more weight.  Black algae LOVES a lime buffet!

Sometimes it is hard to distinguish from a roofing problem.

Asphalt shingles can sometimes be damaged on installation and a pin prick spot opens up and becomes a problem.  Over time the asphalt can begin dripping out.  The single point of such a black discharge may be what you see in the lower right corner of this roof, and under the window.

But that could be black algae also!

The drippy black on the top right of the roof is likely black algae.

I have been told by more than one roofer that this algae is one way to date shingles.

It seems the black algae begins taking hold and manifesting on shingles at about 8 or 10 years of age.

That time frame has proved true on my inspections.

 

So, what can a homeowner do?

Well, you already know NOT TO PRESSURE WASH IT!

Be sure your shingles are not old and fragile.  If so, you may as well replace them.  Then, test your cleaning on a small area to see if it works.

The algae must be killed for any cleaning to be effective.  The oxygen cleansers (sodium percarbonate) will clean the roof, but not necessarily kill the algae.

One formula I found is this:

Tri-sodium Phosphate (the substitute, not the original which is environmentally unsafe) can be diluted and sprayed onto the shingles.

THE RECIPE:

4 Gallons Water mixed with 1 Gallon Bleach.  Stir in 1 Cup of TSP (phosphate free) until diluted.  Tri-sodium Phosphate can be obtained at any hardware or paint store.  Remember to use the safer phosphate-free mix.

Spray on the roof, let it sit for 15 or 20 minutes and rinse off with a hose.

This black algae is aggressive and hard to get rid of.  So good luck!

My recommendation:  when you see what is likely black algae on a roof, it is ugly but does not eat the roof very quickly.  And it might be an indicator as to shingle age!  It can be cleaned!  All three of the roofs above are 12 years old and in the same neighborhood.

 

Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

Office (703) 330-6388   Cell (703) 585-7560

www.jaymarinspect.com


Comment balloon 42 commentsJay Markanich • July 22 2010 06:42AM

Comments

Thanks for the recipe for cleaning the roofs.  There are companies out there who will pressure wash roofs to which I say "Don't do it!"  This is helpful information to give homeowners so they will know the correct way to get rid of these unsightly stains.

Posted by Kathryn Maguire, Serving Chesapeake, Norfolk, VA Beach (GreatNorfolkHomes.com (757) 560-0881) almost 8 years ago

Very interesting.  Seems to me that a smart handyman company would promote this cleaning service. 

Not something I'd take on myself. 

Posted by Lenn Harley, Real Estate Broker - Virginia & Maryland (Lenn Harley, Homefinders.com, MD & VA Homes and Real Estate) almost 8 years ago

Kathryn - again, there are gentle ways to clean things without pressure washing!  Good for you for saying no.

Lenn - I bet you can hit a lot more clay from a roof than you can on the ground...  The handymen do promote this service, and they kill the roof.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

I have the algae on my 10 year old roof with 40 year Timberline shingles.  Cleaning is only a temporary solution as the algae will return. 

I am seriously considering a metal roof as a long lasting alternative to this organic material. 

Posted by Glen Fisher (National Property Inspections of Southern New Jersey, LLC) almost 8 years ago

Good alternative Glen!  And that roof will long outlast you.  What a selling feature.  "Your grand kids will appreciate this roof as much as you do..."

Did you try TSP and bleach?  Having never used it, I'd like to know how that recipe works!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

YEOW!~!  Dating the ROOF by the algae * I KNOW rings in trees so this is a natural * pretty soon we'll be back to SOD Roofs.

Posted by Wallace S. Gibson, CPM, LandlordWhisperer (Gibson Management Group, Ltd.) almost 8 years ago

Wallace - I hear they worked well.  Never inspected one though.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

We used to get it in our pool in CA, and it was difficult to get out

Posted by Bill Travis, Broker/Owner (Captain Bill Realty, LLC) almost 8 years ago

Do not pressure wash, do not pressure wash, do not pressure wash. Excellent post Jay. I am still amazed driving around town and see people up on there roofs with the long hose from the pressure washer stripping the roof right off the house.

Posted by Troy Pappas, Virginia Beach Home Inspector (Safe House Property Inspections) almost 8 years ago

Wow, Bill, I would have thought the chlorine in the water would ward it off!

Troy - it is amazing.  Then a year later, when the granules are gone, and the roof curls and cracks, they blame the shingle manufacturer!  "Those stupid shingles only lasted 10 years!"

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

Jay - It's certainly common in my area, and though it looks awful, most homeowners just ignore it.

Posted by John Mulkey, Housing Guru (TheHousingGuru.com) almost 8 years ago

My understanding, John, is that it has come north annually and gradually from the south.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

Thanks for this post, Jay.  I have always wondered what exactly that was on the roof.  How does it get there to begin with? (airborne, etc?)

Posted by Bruce Walter (Keller Williams Realty Lafayette/West Lafayette, Indiana) almost 8 years ago

Bruce - it is an algae so it can be spread by workmen's shoes and hammers and maybe the air!  I honestly don't know.  Roofers tell me that their hammers can spread it.  And based on the comments I am learning how far and wide it is.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

Jay, since it really does no harm and more harm could be done by removing it, I say learn to like the look :)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) almost 8 years ago

Mainly I see moss and green lichen. The basic moss killers seem to control both for a year or two.

Posted by Steven L. Smith, Bellingham WA Home Inspector (King of the House Home Inspection, Inc.) almost 8 years ago

Another great tip...I like the idea of having a metal roof the best, though!  Especially when it rains...that is, if we ever see rain again. Thanks!

Posted by Susan Haughton, Susan & Mindy Team...Honesty. Integrity. Results. (Long and Foster REALTORS (703) 470-4545) almost 8 years ago

It was actually when the chlorine level got low. One time it was my fault, so I hired a pool service. They let the chlorine get low once and I got the black algea again. So I got a new service, a guy who did his own work and didn't hire the work out to people who didn't know what they were doing.

Posted by Bill Travis, Broker/Owner (Captain Bill Realty, LLC) almost 8 years ago

Charlie - around here that seems to be the thinking!

Steve - I have heard that.  Does what controls all that also damage the grass and plantings?

Susan - I do too and it will last quite a while!

Bill - that splains it!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

Thanks for the post Jay. It is everywhere down here. Does anyone know how long the cleaning lasts?

Posted by Bill Saunders, Realtor®, www.BillSellsHotSprings.com (Meyers Realty) almost 8 years ago

Jay, remember to contact the shingle manufacturer for applicable warranty coverage prior to performing any work on the roof. 

Posted by Jim Mushinsky (Centsable Inspection) almost 8 years ago

I imagine you are inundated with it Bill.  And no telling how long the cleaning lasts.  It does kill the algae, so you might get a few years out of it.

Jim - I expect most people that buy and then live in houses would have no idea who the shingle manufacturer is!  We have been in our house 13 years, and built the house new, and I have no idea!  Probably no warranty would apply at all.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

They say that ignorance is bliss. Before i read this post I was very blissful about the black streaks on the roof and now I will probably stay awake nights thinking about those tiny microbes eating away my house from outside in. When I have seen it, I did think that the covering was eroding and the underlayment was showing through

Posted by Ed Silva, Central CT Real Estate Broker Serving all equally (RE/MAX Professionals, CT 203-206-0754 ) almost 8 years ago

Thanks for the info Jay. I didn't know how to clean it off.  I'll try that as soon as I'm sure I won't melt getting on the roof.

 

Posted by Jack Gilleland (Home Inspection and Investor Services, Clayton) almost 8 years ago

Have you ever tried zinc strips?  My parents cabin has a garage roof that is covered in moss, and I intend to install a zinc strip to see how well it deals with the moss.   I'll post my results in a month or two.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 8 years ago

And that's hard to tell Ed.  But the algae seems to be more general, with few pinpoint beginnings.  Don't lay awake!

Jack - maybe early in the morning.  They say to let the stuff sit only 15 or 20 minutes, then hose it off.

Reuben - I have heard of zinc and copper strips.  I was reluctant to put it in the post as I don't know how well it works.  You can see where galvanized stuff is on the roof that the shingles are clear below it, so that is probably the zinc taking hold.  But let me know!  I wouldn't know how long it takes.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

Actually copper strips are the cure. Take a look at any roof with black algae that has copper flashing. The roof will be clean below the flashing. Algae resistant shingles have copper in the granule coverings. I have been told the copper wears away in about 10 years. Just in time for the algae to show up :)

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) almost 8 years ago

Lately Jay it hasn't mattered much, early morning seems as hot as the afternoon.

 

Posted by Jack Gilleland (Home Inspection and Investor Services, Clayton) almost 8 years ago

Jim - I have heard about zinc and copper, but have not seen them in action.  I was a little reluctant to include them in the blog.  But I see where under a galvanized (zinc) furnace vent there is never black algae.  So it must work.

Jack - Yep!  I left at 7am this morning for my first inspection and it was 81F!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

Decorative copper was used on theeak of the slate roof of the Biltmore House in Ashville for lichen and moss.

Posted by Bill Saunders, Realtor®, www.BillSellsHotSprings.com (Meyers Realty) almost 8 years ago

Bill - then it's been there a long time!  Must work...

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

Thought it was interesting this morning.  This house reminded me of you.

Black Algae on Roof

Posted by Jack Gilleland (Home Inspection and Investor Services, Clayton) almost 8 years ago

And to think that house reminded you of me!  Jack, I have the vapors...!  (Fanning my face even now)   (;~)

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

Jay, thanks for a most informative post.  Reblogging for the benefit of local readers as this is sometimes an issue in South Louisiana. Thanks.

Posted by Derenda Grubb, GRI, ABR, CRS (CENTURY 21 Mike D. Bono & Co.'s) almost 8 years ago

Very informative info.  I've seen many roofs around here with this "stain" and just assumed it was a stain from moisture on homes built amongst trees, shade, wet leave stains.  Now I have a better suspect.  I'll re-blog for folks in our area.

Sue of Robin and Sue

Posted by Robin Dampier REALTOR®, Hendersonville & Western NC Real Estate Source (Coldwell Banker King) almost 8 years ago

Derenda - I am sure you get a lot of this algae down there.  And thanks for the reblog!

Sue - thanks for the reblog too!  And again, I am sure it is very prevalent where you are...

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

Jay - Your the MAN!! I like others above, have always wondered what those stains were! Now we have a professional opinion! Thanks!

Posted by Paige Walker, Real Estate Guru - Alexandria Pineville LA (Paige Walker) almost 8 years ago

Well, Paige, that is what I have been able to find out.  Down there you must experience it a lot.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) almost 8 years ago

I know it seems like I forgot about those zinc strips, but I didn't.  I didn't see any noticeable results after a couple months, so I turned this in to a longer-term project.  I have some fantastic before and after photos to share next week.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

I looked into those zinc strips and my roofer friend said don'e even try it.  They only work for about 5 or 6' down the roof.  So I would need to put about 4 strips on my roof!

That's my house there in the two lower photos.  It's worse now, despite three treatments!  That stuff is pervasive.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

I've heard roofers make the same proclamation, but I'm not so sure.  My experiment was for a moss covered roof, but I think the results would be similar for algae stains.  Hmm... maybe I'll put up a zinc strip on my own house and report back in about three years.  

You should do the same, and do it before you clean your roof.  Maybe it will slowly get rid of the black stains?

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

It might, but the lower roof would certainly be less cared for.  My neighborhood association is hitting people up for this and recommending a "cleaning company" that I think is related in some fashion to the HOA Nazis.  They claim to use the technique recommended by ARMA, but if you read the ARMA site they say their process lasts 18-24 months!  Tha's a lot of money for short term!

The 6" zinc strips would cost about $250 for my roof, about 100'.  Plus installation since I don't want to do it!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

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