Building With the Future in Mind Since 1955

This section doesn’t highlight a particular project.  We’ve included it here because of this common, recurring question:

My roofing is looking old and mismanaged… moss, algae and stains continue to grow!  What can I do?”

As part of our design services, we offer what we call a Pre-Remodel Condition Evaluation (PRCE).   Go here to see an example of a resulting report.

This report is similar to a home inspection report you may request while selling or buying a home. We, however, focus our PRCE on the elements of the home that may need attention in addition to, or instead of, a larger remodel project.  If you have significant issues with your home’s structure, mechanical systems or envelope (roof, siding, windows, exterior doors and crawl space), you may want or need to attend to these problems before spending money on a new bathroom, kitchen makeover or addition.

It is our belief that the greenest projects start with simply taking care of what you already have.

Isn’t the same thing true from an economic perspective as well?  If you allow deterioration to continue, repair costs will do nothing but increase over time.  And that cost may go up exponentially, as opposed to geometrically, once this problem reaches a tipping point.  Certain wood destroying organisms, for example, need pre-existing rot in order to create a home in your structure. Rot happpens and then bugs can call that home. The damage, and the costs to remedy the situation, then accelerate.

We’re driven to repair these problems and the Pre-Remodel Condition Evaluation serves as our diagnostic tool to discover them.

We have found that one of the areas of a home that regularly gets forgotten or overlooked is the roofing.  Ironically, this part of the home is at the same time the most important barrier to protect the rest of your home, and it is also the most vulnerable.  It is also one of the most expensive to replace, and the damage that occurs from a leaking or failing roof often goes unseen or overlooked for lengthy periods of time in unseen areas of the home.  This can result in significant damage to attics, ceilings, walls and siding… the price of which to repair may far exceed even the replacement of the roofing.

We recommend that you or someone you trust  inspect your roof, gutters, fascia and all penetrations at least once, if not twice, a year, and  any maintenance issues be taken care of immediately.  Additionally the roof and gutters should be kept clean.  Debris left on a roof and in gutters can severely reduce the life of the roof  and create conducive conditions for other problems to develop.

The first step to maintaining your roof is to make sure it is clean. In our environment there are a lot of molds, algaes  mosses and lichens that thrive on roof surfaces, especially with the persistent inclement weather that we experience in this area in the winter and spring months.  Once the roof is clean, keeping it clean is key to extending the life of any roof.

There are many approaches to roof cleaning. Ask five building professionals for their honest opinion about best practice, and it’s likely 6 answers will emerge.  Roof cleaning techniques are controversial.  Perhaps the technique most universally avoided is high pressure washing.  This destroys the surface of composition roofing and may damage the coating on metal and tile roofs as well.

Types of organic growth

There are several types of organic growth that can occur on roofs.  All of these flourish if organic debris is not removed from the roof surfaces.  Any of these can take 5-15 years off the lifetime of a roof.  Below are the most common in our area:






Algae lives on dust, pollen and organic debris.  It’s growth is triggered by dampness and typically occurs on, under and around the granules that make up the surface of the roof.









Lichen is a fungus that exists symbiotically with internal algae.  It receives food from the algae through photosynthesis, and provides protection for the algae.  Together they form a lichen.   They put out tentacle-like roots  deep into composition roofing, breaking down the asphalt granules and creating pock-marks and stains .










Roof moss thrives in damp, shaded areas.  Hence, the more active growth on shaded or north-facing roof planes.   Like lichen and algae it puts roots into the roofing materials and the areas between shingles.  Additionally it retains moisture and keeps the roof damp, promoting further growth, as well as hastening the degradation of the roofing materials.







Preventing the need for roof cleaning

Here’s what Practical Pressure‘s website at has to say (a company that doesn’t work in our local area) …

The best way to care for moss and algae on your roof is to prevent it. You can do this by applying moss killer annually or biannually or in some cases zinc strips may help to a limited extent. However zinc strips do seem to lose their ability to prevent moss over time and in some cases moss is even seen to grow on the zinc itself. Thus we would recommend regularly applying some kind of moss killer instead. You can find granulated or powdered treatment at your local hardware store or make your own bleach solution at home which can be applied by using a pump garden sprayer, some people just use baking soda or laundry detergent (which may not be good for the environment). The important thing is to kill the moss before you see it growing, don’t wait until it is a problem before you apply treatment.

The most common problem, when it comes to preventive maintenance, is usually not due to an inability to perform the needed care but rather, due to our very busy lives, we most often just simply forget or never find the time until the problem has already resurfaced and it is too late.

…  by avoiding the wear and tear caused by moss growth and pressure cleaning you can expect to get more years out of your roof before having to replace it.

If you’re going to prevent moss yourself, here’s one possibility, again from Practical Pressure’s website (unproven by us; use at your own risk):

Please note that this particular mixture and method is not specifically used or indorsed by Practical Pressure, it is taken from outside source material which appears to be credible but carries no guarantee. Use at your own risk and discretion.

       Bleach Solution: 1 Cup Liquid Chlorine Bleach1 Cup Powdered Laundry Detergent1 Gallon Hot Water1Garden Sprayer
       Directions: Put on your Safety Glasses. Mix ingredients in the sprayer and then spray it onto your roof, starting from the bottom and working your way up to the ridge. (Do Not Walk On the Roof Where the Solution Has Been Sprayed it Will Be Slippery). Let it sit for about 15 minutes and then rinse it off with a garden hose.

Otherwise, call around and hire someone to manage your scheduled moss prevention program.

Roof cleaning methods

If you’re reading this section, prevention didn’t solve the problem.  It’s time to clean the organic  growth off of your roof.  So what do you do now?

Unfortunately, no matter which roof cleaning method you choose, there’s some compromising going on!  Let’s briefly review your options…


Many roof cleaning companies offer “chemical” cleaning.  This is usually done by spraying a combination of different chemicals and each company seems to have it’s own proprietary concoction.  Most claim it is “bio-degradable, “non toxic” or “environmentally friendly”.  We have questioned a couple of [now out of business] roof cleaners who claimed ‘environmentally safe’ methods. Neither could satisfactorily explain how they knew this was the case, so we’re leery of anything except baking soda, which is just calcium carbonate. The purpose of this type of cleaning is to both kill the organic growth, as well a remove the staining caused by algae.  Often it is necessary to return to the roof a few weeks later to blow or broom the debris of the dead materials from the roof surface.  Regardless of the exact materials used, we recommend that you carefully choose a roof cleaning contractor.  Make sure you trust them and understand what chemicals they are using. How they are going to protect your yard, landscaping and the surrounding areas — especially if you live in a watershed — from the run-off?  Many companies will actually collect the runoff from the gutter system and take it off site.  What do they do with it then? You need to know.

The various moss-killing powders, including the bleach/baking soda alternatives, do not remove existing moss; rather, they kill it by changing the chemistry of the roofing surface. At least 5 gallons of the spray-on mix is needed to cover even a small roof because the entire roof surface has to be soaked. If clumps of moss are visible, these might be killed if applied concentrations are sufficient, and contact is long enough.  But you will still need to wash the roof to flush off the debris [or plenty of gravity and time! ]. Gutters will then need to be cleared out. If the moss killing solution is washed off  toosoon without soaking in then insufficient time will elapse to kill the moss. So we recommend spraying on the solution and just leaving it alone without rinsing. If the weather is dry enough that the solution dries out and becomes a white powder, and if that is unsightly, THEN rinse it off. Otherwise, leave it. NOTE THIS:  the roof will be very slippery with these wet solutions, whether baking soda, bleach, or some other mix. Plan the application and the retreat to the ladder before beginning your application. And know that these applications are very temporary, washing off when you rinse dead moss off or in the next good rain. Consequently, they need to be reapplied at least once per year.


You’ve probably seen and heard about this technique.  Usually you’ll see a narrow silver line of zinc just below the ridge shingle. While these do tend to help some, their aid is limited:

      1. They lose their effectiveness over time, leaving you with a rather unattractive silver line.
      2. Their effectiveness decreases the farther the shingle is from the strip, so the effectiveness varies a lot.
      3. You’ve added a large number of fastener penetrations into the the plane you are relying upon to prevent water infiltration!
      4. Over time the zinc is leaching out of the metal strips and entering our storm water and groundwater… not good.

Our opinion: although it makes some difference, zinc strips do so for a short duration and it’s generally not potent enough to do the trick.  Yes, there are zinc powders (see the ‘chemicals’ section above) available that can be hand-applied to the roofing, but we’re again introducing chemistry that will find its way into our surface and ground water, thereby making third-party verification of its possible environmental side effects very important.


This work largely by removing the roofing granules! Not good! Avoid this, unless using a soft nylon brush and you are willing to leave some moss behind. Scraping right down to the granules will cause damage eventually.


This method uses a very low pressure (160 p.s.i. or lower) combined with high volume water to wash the roof more gently.  It is often combined with hand/brush scrubbing difficult areas to remove the root systems of moss and lichens.

The important note here is that the the roof gets cleaned as gently as possible.  After the roof is cleaned it is far easier to keep it clean.  At our office, showroom and shop in Bellingham, we clean our gutters, inspect the roofs of our  buildings, and blow off the debris with a backpack leaf blower at least four time a year.  If any growth has happened since the last service we gently remove it by hand with a stiff bristle brush being careful to not damage the roofing.

We have also installed roof anchors in several location so it is easier and safer to access the roof.  We recommend that whenever you repair or replace your roof, make sure you add anchors at the same time.  The expense is minimal and makes it far easier to service the roof in the future. Install as many anchors as needed, in order to conform to L&I rules. Sometimes more are needed than you might think, depending on the ‘pendulum’ factor of a potential fall.  {What? Your contractor isn’t covered by L&I? DO NOT HIRE THIS PERSON! You may be liable for the injury!}  Be sure the anchors are properly fastened to the roof  rafters and not just into the sheathing!

Costs for the initial cleaning, if you have substantial organic growth, is going to range from $500 to $1,500 depending upon method, roof size and slope,  and level of growth.  After the inital cleaning we would suggest a budget of $400-$600 per year, for inspection and debris and gutter cleaning.  Additionally we would suggest hiring a professional that you trust and then get on their schedule.  Many offer yearly plans and once they have cleaned your roof should be able to tailor a maintenance plan and schedule to meet your needs.  Unless you are experienced and very comfortable on your roof, hire someone to help you.

Most new composition roofs that we install, or subcontract to a roofing company, cost between $5,000 and $9,000, depending on size, steepness, complexity and roofing material choice. Typically they have a life expectancy of 20-50 years.  If not kept clean and maintained this could easily decrease to 15-30 years.

Our Conclusion

Given the expense and importance of this part of your home make sure you take care of your roofing.   Prevention is the key.  Cleaning techniques, if prevention didn’t do the trick, are varied and controversial.

The above writeup points to low pressure/high volume as our preferred methodology.  It seems like the best of the available evils.  While the damage done to the actual roofing seems minimized, what hurts is the need to use so much potable water.

Here’s a well-written section of Practical Pressure’s website at  The question posed is this: will pressure washing damage my composition roof?

A straight answer would be yes. If you asked if water will damage a composition roof the answer would also be yes. If you asked if direct sunlight will damage a composition roof the answer would also be yes. All three of the above are going to create wear and tear on your roof but not to the extent that a person should feel concerned each time their roof is exposed to one of them. Having worked several years in the roofing trade I often heard you should never pressure wash a composition roof, now that I am in the pressure washing business I hear that sentiment expressed with increased frequency. The fact of the matter is that in most cases that is very true. I have been on many roofs where someone preceded me with a pressure washer and destroyed every section of the roof they had set out to clean via pressure washing. If a person is not familiar with roofing systems and experienced with the accessories and functions of a pressure washing machine KEEP THEM OFF OF YOUR ROOF.

Now on the other hand I have yet to hear someone who is experienced and well practiced in the pressure washing trade express that a composition roof should never be cleaned with a pressure washer (they all do express a need for caution). Someone who knows how to regulate the output pressure (psi*) of their machine can easily drop it down to a much safer working level. Knowing the different accessories available for pressure washing is another must. Some nozzles have an output spray which is many times more abrasive than others. Being familiar with using a pressure washer also allows a professional pressure cleaner to account for the angle at which the spray is directed at the roof as well as the resulting deflection spray. Instead of being a danger to your roof, when the above credentials are met, having your roof pressure cleaned becomes a valuable tool in ensuring the longevity of your investment.

Moss is Dangerous

The opening comment of this article affirmed that pressure washing does damage a composition roof. However when done correctly it will do no more damage than the simple wear and tear that rain, standing water and the sun are constantly bombarding your roof with. By all means Practical Pressure strongly suggests that you take every effort necessary to keep moss from ever growing on your roof so that pressure washing is never needed. However at times it is necessary given the circumstances. To Illustrate: Chemotherapy is not “good” for the human body but when cancer strikes it may be absolutely necessary for a person to be treated with it, and many people have enjoyed a satisfying and prolonged life as a result of accepting the treatment. Pressure washing a composition roof covered in moss is very much the same, though pressure washing is obviously going to produce a limited amount of wear and tear, in the long run it can, in large measure, actually increase the life of the roof. The effects of moss growth on your roof can be devastating even after a relatively short period of time. Moss often strips the protective granulated surface off of the shingles it grows on and can even go so far as to eat holes clear through the roofing. The sooner you have it removed the longer your roof will last. Even roofs which have been pressure washed multiple times by a professional pressure cleaner have proved to be in much much better condition than a roof that was left uncared for when moss began to appear.

It is true that there are other ways to remove moss from your roof but usually the alternative is not an improvement over pressure washing. Some common instruments I have observed or heard reported to have been used to remove moss are: screw drivers, flat bars, pry bars, putty knives and wire brushes. Certainly it could not be said that these instruments provide a less abrasive or less damaging method of removing moss from a composition roof. It is possible to kill the moss with out pressure washing by using things such as granulated and powdered moss killers but even then the moss will most often stubbornly cling to the roof and continue to hold moisture. Live or dead moss will retain water on your roof subjecting it to decay and it will also assist in collecting other debris to pile up on your roof.

So in consideration of the above factors Practical Pressure can, in good faith, adamantly state that your roof is being well served when it is pressure washed by an experienced professional. 

There aren’t many companies out there using low pressure equipment (160 psi or lower) so be sure to verify just what pressures are being used by a company you are considering to hire.

For years now we’ve been happily working with Professional Roofcare‘s Dave Tucker.  He’s licensed, insured and bonded and can be reached at or at work at 360-734-9743. We know he’s using this 160 psi equipment. And Dave had this to say about this writeup about roofing maintenance…

“I very strongly urge homeowners NOT to do this low-pressure washing themselves unless they understand vectors and pressure: the direction that force is applied to the roof relative to shingle edges, near penetrations, flashings, etc. It is amazingly easy to cause a leak. These don’t normally become permanent, but if sheet rock gets wet because the flashings were substandard, or because water went the wrong way into a good flashing…well, you know about that, Rick.”

We sure do, Dave, and we’re trying to save our clients this headache and avoidable homework!

Dave also suggests that a liberal application of baking soda on one’s roofing is a proactive way to create an environment that minimizes the growth of algae, moss and lichen. In the fall of 2014 our local Costco was selling 13 pound bags of baking soda.

When is this baking soda best applied, Dave?

“Aim for the fall, when one’s roof is damp from heavy dew, and its re-wetted nearly every night with dew or from light fall rain. This helps to distribute the soda. Wind is light in the fall, so that helps keep it on the roof. Avoid periods of heavy rain [winter]. Best strategy: watch the weather forecast and do it when there is light rain in the forecast. Pre-wet the roof with a hose so the soda sticks, then lightly spray the soda to begin the ‘trickle down’ over the roof if the rain in the forecast doesn’t materialize.

“Of course, if you apply it and then we get a gully washer , you’d need to reapply.

“Biologically speaking, I don’t know that there is any better time of year than another for applying the baking soda.”

Dave, do you spread baking soda as part of your roof cleaning service?

“Yes, I spread soda on roofs I have cleaned, or on roofs that do not need cleaning. I usually don’t do it right after a roof cleaning, though there is of course a tiny amount of moss left over. I usually spread soda within a year of cleaning and annually after that.”

You probably didn’t think caring for your roof was going to be complex and controversial; hence this write-up.  We, too, wish this topic was straight forward.

Sure hope this helped.


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