Tag Archives: Roof moss

Never pressure wash your roof

Never pressure wash your roof.

We were called in to fix this mess


Let’s talk about contractors who want to pressure wash your roof.   As a general rule, anytime a contractor wants to sell you a roof cleaning that involves the use of a pressure washer, they are VERY NEW to the roof cleaning industry, don’t understand it, and should probably be avoided at all costs..

In this article, I will explain why  pressure cleaning  roofs and the new “eco friendly” cleaning companies and chemicals that are appearing , should not be a part of the discussion when you are thinking about having your roof cleaned.

As the roof cleaning industry grows here in the Raleigh/Cary area,  I am hearing more about contractors who are actually using pressure washers to clean roofs.  It seems to be a mix of new companies coming into the market, and existing pressure washing companies that are  adding roof cleaning to their service for an additional revenue stream.  It does not matter who is doing it, you should never allow any type of pressure washing to be done on your roof.


Eco friendly roof cleaning ???

Our area in this part of the state is pretty fortunate not to have more than a couple of the “Eco Friendly” roof cleaning companies.  The claim is that the chemicals they use, which are mostly sodium hydroxide, are Eco Friendly and will not harm plants, animals or the environment.  Try asking them for a copy of their MSDS (Material Safety Data Sheets) and you will get a little different story.

Here is the bottom line on any type of “Eco Friendly” roof cleaning:  IT DOES NOT EXIST.  How would one expect an Eco Friendly product to kill the algae on your roof?  It doesn’t.  Once these chemicals are applied, they turn greasy and black.  The only way to get it, and the algae off your roof, is with a good deal of pressure using a pressure washer.  A garden hose will not work.

Store bought roof cleaning chemicals or do it yourself roof cleaners are nothing more than gimmicks that do not work.  There are a couple of pictures in the link above that really show everything you need to know about store bought, roof stain removal products.

Reading the warning label on some of these products will serve to convince you on just how “Eco Friendly” they are.

In case you are doing a lot of reading on the subject here is another great article on store bought roof cleaners.

Pressure washing a roof?

If you are thinking about having your roof cleaned, make sure no type of pressure washer is going to be used.

That means this:

This picture above is from askthebuilder.  He swears he was not destroying the shingles but I respectfully disagree.  He is using a high pressure wand with a green 25 degree tip.   There will be lots of granule loss and lifting of the shingle tabs.   

Or This:

This device is a surface cleaner.  It is generally used to clean concrete utilizing high pressure. Underneath, you will find two high pressure nozzles attached to a rotating arm. (Picture a lawn mower blade)

Some companies are “modifying” these to clean roofs.  The cleaner will stand at the top of the roof, lower the surface cleaner down the roof pitch with a rope, and then pull it back up.

The general sales pitch associated with these companies is that they have modified the machines for lower pressures or they hold the wand high and away from the roof so there is less pressure hitting the roof.

Having been around the business for a while, I can tell you with a fair amount of certainty, that an older roof would not withstand the onslaught from a pressure cleaning wand, or one of these machines.  Read why below.



Using a pressure washer to clean a roof does two things:

  • It lifts the shingle tabs and breaks their seal.
  • It removes the protective surface granules on the shingle.

Asphalt shingle roofing systems are usually installed as a restrained tab or a self- sealing system.  That means that each shingle has a sealant strip on it so that when they are installed correctly, each row of shingles will adhere or seal themselves to the row above and below them.

This black strip holds the next row of shingles down

Picture is from homeconstructionshop.com

Asphalt roofing systems are designed to withstand a certain amount of wind load.  It is this self-sealing shingle system that makes you roof wind resistant and keeps your shingles from blowing off the roof during most storms.

When a pressure washer is used to clean a roof, regardless of how careful the wand wielding cleaner is, there is a high probability that some shingles are going to get lifted and this seal will be broken. This leaves your shingles “flapping in the wind” during the next storm.

You will also lose a lot of the surface granules from your shingles.  These granules play a role in protecting the shingle and helping to reflect the sun’s rays so your attic stays cool.  The older the roof, the more granules you will lose in the washing process.

There is only ONE approved method for cleaning a roof.

There is a trade association called ARMA that represents most, if not all, shingle manufacturers.  When you have a question about roofing (of any kind) this is the place people come to get the answer.  ARMA issues technical systems bulletins (TSB) on just about ever type of roofing out there.

They have issued a bulletin about the proper way to clean an asphalt shingle roof  that is extensively referred to by professional roof cleaners in our industry.    It involves the use of low pressure and a light bleach mixture.  That is it.  There is no other method that is approved.  If someone is washing a roof using a pressure washer or one of the devices pictured above, they will usually have a hard time getting insurance.

I am seeing the term “low pressure roof cleaning” used a lot by these  companies who are using the pressure washers.  It is part of a slick marketing package and quite frankly, it is a smart move.  They don’t have to actually define the amount of pressure they are using to clean your roof, they just tell you it is low pressure and leave it at, that hoping the terminology fools you.

I hope this article helps to present at least one side of the argument.

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