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How To Knock 10 Years Off Your Shingled Roof's Lifespan In 90 Minutes

This is a simple post about common sense.  How to knock 10 years off your shingled roof's lifespan in 90 minutes.  And how?  By knocking off the shingle granules!

Getting home I heard it.  A pressure washer was nearby.  I have written posts before about pressure washers.  They damage houses.  Especially decks.  It may be alright to lightly pressure wash a deck, after other cleansers have been used, but in my experience I don't see a light pressure used, or a wide nozzle.

But this pressure washer was across the street.  And looking, I feared it was being used on the roof!

Our neighborhood has experienced severe roof algae problems (called "stains" by the HOA) and most everyone has gotten notice to clean their roofs.

This particular neighbor unfortunately looked at my ugly roof for years!  And they apparently also saw my experimentation on cleaning it, and the final result when I developed a formula that worked.

Walking around back I saw what I had heard.

My neighbors were having their roof pressure washed!

(So much for getting advice from their friend, the home inspector, across the street!)

Look at this photo.

The nozzle is right against the shingles, it is a 10 degree nozzle (which highly ramps up the spray as it focuses it more narrowly), and the over spray indicates that very high pressure is being used. I watched him absolutely massacre the rubber collar on the roof vent!


Suspecting that the pressure was too high, when I saw the big-box-store machine in the front yard I could only shake my head.


What may seem like a good deal really, really is not!

The Asphalt Roofing Manufacturer's Association (ARMA) has an article on cleaning roof algae here.  Notice the last line:  "High pressure washing systems for algae removal should not be used."  Believe me, 4200 psi is very, very high pressure!

Even when you go to a typical homeowner site, like here, roofing professionals all say not to pressure wash!


1.  It is removing the protective granules from the roof shingles, blasting them away!  Those granules will typically wash away with time anyway, due to rain.  Why speed up the process so dramatically?
2.  This process uses water.  If rain spreads the algae, called gloeocapsa magma, pressure washing will not kill it.  Gloeocapsa magma is a VERY aggressive algae that attacks the limestone in the roofing granules.  It adheres to those granules and does not give up easily.  This process might make the roof look temporarily clean, but it is not getting all of the algae.  It will return, with a vengeance!
3.  True damage is being done to the roof shingles, and any roof penetration.  Literally this pressure is washing years off of the roof's future!
4.  My formula cleaned my entire roof for $35!  Does any other process, including this guy, cost $35?

All the roofing manufacturers say to use a formula that combines chlorine and TSP.  I used the environmentally-friendly tri-sodium phosphate powder in my formula.  A biochemist friend told me that the TSP bonds with the algae, causing it to release from the limestone, so it can be killed by the chlorine.  The TSP remains on the roof, bonded also to the limestone, kind of providing an additional protective coating.

My recommendation:  when you want to do a homeowner project, consult with a home inspector!  We are an informed group, have no financial interest in offering advice, and will never steer anyone toward doing something that benefits the home inspector!




Jay Markanich Real Estate Inspections, LLC  

Based in Bristow, serving all of Northern Virginia.

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


Comment balloon 74 commentsJay Markanich • November 29 2012 02:31AM
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