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

Jay shares very good information on his blog.  This one especially.  We all know how annoying that moss and coloring of our roof shingles can be BUT NEVER, use a power washer to clean your roof.  Read his blog for yourself. Thanks Jay!

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 pressure washing their roof!

(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

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All pictures, text, etc. stated within is the exclusive property of Bobbie Smith and cannot be copied or duplicated without written consent from Bobbie Smith.  All statistics and data contained herein are obtained from reliable sources and are deemed reliable however each individual should always do their own research on each topic and derive their own conclusions. Any statements of opinion are just that, the opinions of Bobbie Smith. *Realtor is a registered trademark of NAR*

Comment balloon 14 commentsBobbie Smith • November 29 2012 04:53AM


Good morning, Bobbie....this was a great post to reblog.... so many people powerwash everything.... it may look good initially but they pay the price later...

Posted by Barbara Todaro, Marketing Agent for The Todaro Team (RE/MAX Executive Realty ) over 6 years ago
Thanks for reporting. We have this problem around Charlotte too.
Posted by Lori Williams, Lake Wylie, Gastonia, SW Charlotte, Homes for Sale (Lake Wylie, Charlotte, Gastonia Homes for Sale ABR, CDPE, SFR, ASP, over 6 years ago

Interesting. I never thought about it but pressure washing does not seem logical.

Posted by Gary L. Waters Broker Associate, Bucci Realty, Fifteen Years Experience in Brevard County (Bucci Realty, Inc.) over 6 years ago

This is a great selection for a reblog and one that I would have otherwise missed. Thanks!

Posted by Barbara-Jo Roberts Berberi, MA, PSA, TRC - Greater Clearwater Florida Residential Real Estate Professional, Palm Harbor, Dunedin, Clearwater, Safety Harbor (Charles Rutenberg Realty) over 6 years ago

Hello Bobbie,  This is a first, Never seen this before. Good re-blog.  Hope you did not get much snow the other day.

Posted by Will Hamm, "Where There's a Will, There's a Way!" (Hamm Homes) over 6 years ago

Thanks for the reblog Bobbie!  And I am truly embarrassed for you Barbara-Jo.  Truly...


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

Hi Barbara, Thanks, I agree. May seem like a good idea when you think about but thankfully Jay saved us from making this mistake.

Posted by Bobbie Smith, 570-242-1891 over 6 years ago

Hi Lori, Seems wherever you have humidity, and maybe too many trees, it is a problem. Jay was very helpful

Posted by Bobbie Smith, 570-242-1891 over 6 years ago

Gary, It is, isn't it. Thank goodness Jay saved us from making a terrible mistake.

Posted by Bobbie Smith, 570-242-1891 over 6 years ago

Hi Barbara-Jo, Glad you caught in on the reblog.  Thanks for commenting.

Posted by Bobbie Smith, 570-242-1891 over 6 years ago

Hi Will, Yes, thanks.  We initially received 3" but as the day progressed, it warmed up and most of it melted off.

Posted by Bobbie Smith, 570-242-1891 over 6 years ago

Hi Jay, Thank you! Great, great info worth spreading.

Posted by Bobbie Smith, 570-242-1891 over 6 years ago


This was an excellent and very useful re-blog.

Posted by Patricia Feager, MBA, CRS, GRI,MRP, Selling Homes Changing Lives (DFW FINE PROPERTIES) over 6 years ago

Great repost and I just can't believe people do this. I saw a guy take out his double paned windows doing this.

Posted by Charles Stallions, 800-309-3414 - Pensacola, Pace or Gulf Breeze, Fl. (Charles Stallions Real Estate Services ) over 6 years ago