Moss Treatment and Control Service Page

We see that here in the Northwest moss build-up on roofs is a huge problem. It is very unsightly and will shorten the life-span of your roof. Here is some good advice you can look into at a reasonable cost, without causing more damage to the roofing shingles than the moss would cause; like the damage pressure-washers will do to the shingles.

If you are not able to do this work yourself, and you happen to live in the Portland Oregon Metro Area, call us to help you out with this problem.

What causes so much moss growth on roofs?

(a) Moss spores are so small they will travel great distances through the air. There is no way to avoid them.

(b) Most of us know that it grows more on the North face of roofing.  This is due to the lack of direct sun light exposure. Moss is not the same as plants. It is a fungus and thrives better in darker areas. One reason it will not grow as well on the South side is the heat of direct mid-day sunlight will dry it out to the point it cannot survive without any water. Thick layers of moss will trap moisture like a sponge for a long time, but on the South sides it does not even get a chance to build up thick, unless there are some shade trees near by.

(c) Moss feeds on the decomposing dust and tree debris that gets trapped on roofs.

(d) You will see heavy build-ups on roof sections that are directly under tree branches, since there is a lot more fall-out of leaves, branches, and sap on the roof.

Why is moss bad for roofing?

Some people think a good heavy layer of moss will save a roofing from exposure to the elements. Some even jokingly say the moss is the only thing holding the roof together. This of course is not true. There is no benefit to moss growth on most any surface. It is one of nature’s ways to help recycle life. It works to eat away and decompose what it resides on.

It may look charming to walk through a forest with huge draping coverage of moss on trees, where you can hardly see the branches, but that is not a healthy sign. Moss will attack sick trees. In more extreme cases you will even see ferns growing on the moss up in the trees. The Forestry department now recognizes how decades of forest fire prevention has actually hurt many areas of Oregon and Washington forests, by not allowing the natural sterilization and thinning of these areas.

How does moss damage composite shingles?

Moss root growth will dig into the roofing shingle surface and up under the overlapping shingles, splitting them apart. Eventually causing leaks. Moss will also hold moisture against the shingles and flashing, causing the bacteria growth to rage and decompose your roofing. Asphalt shingles are very resistant to this decay, but it does have its limits. Heavy moss growth can eat 5 to 10 years life span from your roof if left unattended.

It is common to see roof valleys built-up with debris for several years. Moisture held in suspension, causing that debris to decompose into mud under the surface debris you can see. To the point you will have plants begin to grow out of that mud. Roof valleys and other metal flashing areas are the #1 source of roof failure and leaks.

If the roof is not too old, these areas can be repaired in many cases without replacing the whole roof, but few roofing contractors will admit this to you. Their motivation is to sell you a whole new re-roofing job.

What is the wrong way to clean off roofs?

A Pressure Washer
Make no mistake, a pressure washer is death to a roof! It is true that most contractors will use a pressure washer to quickly and easily blast off the moss and debris that may have collected on your roof.  It is true that a pressure washer is the fastest and easiest way to clean off a roof riddled with debris and moss. It will also clean off the mildew that darkens and stains a roof without any cleaning chemicals, but this is a very harmful way to clean a roof:

Normal house-hold water pressure is only about 150 psi (pounds per square inch). The problem with any pressure washer is how they are designed to deliver 800 to 3,000 psi that will blast a good 30% or more sand off your shingles. Roofing is not designed to withstand more than 100 mph winds, and this high pressured water will be forced into places that can cause a good deal of water damage to your house, as well as your roofing shingles.

Keep in mind that the sand on the surface of the asphalt shingles is needed to act as a shade for the petroleum material these roofing shingles are made of. If you let them remove that much sand off your roofing shingles, it will leave them exposed to the UV rays of the Sun. The Sun will rip the shingles to shreds in a matter of only 5 years or so. This is a good example of how the medicine can be worse than the disease. You are far better off to leave the moss there to grow and slowly eat at the shingles.

Bleach
This is helpful to kill moss, but it is very bad for the environment and the person applying it, so we do not recommend using bleach on roofs. Chlorine was originally designed to be one of the deadliest chemical warfare weapons of that era. It may kill the moss and temporarily stunt it's growth, but it will not remove the moss or make it easier to remove. It may also discolor your roofing. It is very costly as well.

What a common mistake done to keep moss off?

Zinc Metal Strips
Zinc strips have been used to help keep the moss down. This is helpful, but proved to be not as effective as needed in our area. It was only effective a few feet down the roof. This one gray metal strip was unsightly enough. Few are willing to have several mid-strips strung across their roof to keep it free of moss. This would also meant there would need to be hundreds of new nail holes punched through the roofing shingles to hold the zinc strips in place. This zinc is a very soft metal. It is barely stronger than lead. These strips would commonly become dislodged in high winds. The worst part is how these strips would curl up over time like a tape measure blade. They would troth the rainwater, dipping in a few places. There would be clean streaks at those dip points were it would be moss and mildew free, but that made the roof look even more noticeably messy.

Also, this zinc is not be able to remove the moss that is there. See below for how to safely remove the moss.

How does DMR kill or remove debris and moss safely?

Powder Moss Treatment
This is a good and inexpensive way to control the moss growth, but has to be re-applied each year or two. Many people think it is the mild detergent in the powder that kills the moss, but it is actually the ground-up zinc metal that does it. The detergent helps distribute the zinc. Zinc is an inexpensive metal compared to copper, which has shown to have an effective anti-fungal property. It should only take a half hour or so to treat a standard low slope roof on a small house.

Copper roof flashing: T-edge metal, W-valley, and a deluxe ridge cap (designed to have a hidden ridge vent under it) ready for delivery

Copper Hip and Ridge Caps
This is a lot more costly for the initial investment, but it is a long lasting trouble free solution that can be re-used over and over again when re-roofing is required. It is an excellent option for several reasons:
(a) it has enough copper surface to actually do some good against moss growth
(b) it tarnishes to a \n unobtrusive dark brown within a few months
(c) and has a much better lasting seal of the top ridge of the roof than ordinary shingles bent over the top
(d) it is the only product made to be re-used after a re-roofing again decades later, since it is attached with stainless steel screws with metal and rubber washers every 2' on each side.

The 10' long section should overlaps about 4" to 6", so this needs to be factored in when ordering these. It should come down at least 7" or more on each side. The more bends it has, especially near the bottom edge, the stronger and straighter it will be after it is mounted. There are several ways and designs to do this that can add a decorative touch to your roof. This is also a good way to incorporate a hidden ridge vent as well. There are numerous different companies making ridge vent material that is then covered by roofing, but it can be covered with copper just as well. Here is better screened roof vent design for you to consider:

Contact us for more details and pricing.

Custom copper ridge caps made to order

To Safely Remove the Moss
This powder will kill the moss and mildew and keep it from returning, but it will not remove it from your roof. To remove it without too much damage to the shingles takes a lot of patient scraping with a plastic or metal scraper. I have found that a narrow masons tuck point trowel to work best on composite roofs. The abrasive sand has ground the end of the steel squared tip down to a point.

To remove only about 90% of the bulky moss; a garden hoe can work to scrap it off, but it is really tedious since it is not very wide. A better tool is to use a stiff-tooth rake and attach a wider scrapper on it, so not to use the teeth of the rake. A stiff 3" to 4" tall strip of aluminum sheet-metal that is taller than the teeth of the rake is attached on the inside edge of the rake. It is best to have the bottom edge of the sheet metal bent at a 45 degree angle about 1" up, in towards the handle along the bottom to scrape the moss downwards. This bend can allow the scraper to be a few inches wider than the rake. A few small holes are drilled through the sheet-metal to run a few nylon ties through it to fasten it temporarily to the rake teeth.

And of course there is a good deal of messy clean up. A broom is used to sweep the loose moss down from time to time to see what we are doing. A wire brush is too aggressive to the sand on the shingles. A garden hose can be used to sweep down the loose moss and debris, spraying downwards over the roofing only (keeping in mind that water and mildew make a very slippery combination).

Disclaimer:
Most homeowners are not willing to get up on their roof to do this sort of work, but if you are looking to do this work yourself, bare in mind that OCA Safety Standards say you should be wearing an approved and anchored safety harness if you are working higher than 10' off the ground.

With our vast experience we have worked on thousands of different roofs, so it is a lot safer for us. If you attempt to follow our instructions here, we cannot accept any liability for your personal safety or damage that could occur.

What if We Do Not Live There?
If you are not fortunate to be living here in the Portland Oregon Metro Area, this info should help you find the right contractor to do this as we specified. Feel free to insist they read this web site and follow it to the letter. Or just print it out for them to read, and insist they read it there in front of you. If they balk at it or try to debate the validity of this web page, that should be very telling, and you should not hire them! The damages will be your loss, not theirs. You are not likely to get them to volunteer to repair those damages, and it will be very hard to prove their responsibility later on.

What if We Do Live There, in Paradise?
If you are fortunate to be living here in the Portland Oregon Metro Area, we will be happy to assist you with your needs, doing it the right way. As to cost, it is calculated in 100-foot sections, or a 10' x 10' area called a square of roof in roofing terminology. These example prices are based on a small low-slop roofed house (6/12 pitch or less) composite roof, with around 10 squares of roofing (or 1,000 square feet, which is different than the floor space in a house). A medium size house has around 20 to 30 squares of roofing. The cost varies due to the complexities and safety issues to access all the areas of your roof.  Go to our Contact web page and send us an e-mail telling us what you need or may want.

(a) $150 just to treat the roof with this type of powder moss killer (or 15 cents per square foot).  We normally use about twice the recommended amount of moss killing powder.

(b) $400 to do a simple scrape and clean up, removing around 80 to 90% of the debris and moss build-up, and treat the roof with this type of powder  (it is then recommended to do (a); re-treating of moss killer on your roof again every 1 to 2 years after that to keep your roof clear of moss, and some simple debris removal as needed).

(c) $700 to carefully scrape; removing 95 to 98% of the moss build-up, clean up, and to treat the roof (it is then recommended to do (a) again every 1 to 2 years after that to keep your roof clear of moss, and some simple debris removal as needed).

(d) $2,000 to carefully scrape off around 98% of the moss build-up, treat the roof with this type of powder moss killer, and install a 24” wide custom 20oz copper roof cap 30' long. Keep in mind that this should be the last time this needs to be done, and the ridge cap is removable to be reused after a new roofing project is done.  It is recommended to do the $150 re-powdering of the roof only every 5 years or so to keep it clear of moss, and some simple debris removal as needed.

Moss and mildew on metal roofs is more a problem for anyone who needs to access your roof than the deterioration of the sheet-metal. They are very dangerous to access for servicing, since they mildew in short order and become very slick when wet!  Even for a low slop roof.  Wood shakes also moss-up like this and become very slick, but at least workers can wear special cleated boots.  There are no special shoes made to walk safely on metal roofs safely.  There are numerous problems with any metal roof, as described on our Roofing web page.

The moss will hold moisture against the painted metal, causing the bacteria rage and buckle the paint off.  Then resulting in quickly rusting through that thin steel sheet-metal.  Once that steel begins to rust it is too late to just have it re-painted.  The paint may stick to the rust, but the rust will flake off the rest of the steel.  It will have to be carefully sanded down and primed, which is very costly and may cause a penetration to the steel sheet-metal surface.  It is usually necessary to replace the roof at that point.  Replacing only part of the metal roofing could be done, but would be strange to have that older part fail well before the new replaced section.

Also, most any roofing contractors will not even give you that kind of option.  It would not be something they would be willing to do or warranty, even thought the CCB only requires a 1 year warranty on construction. There incentive is to sell you a complete new roofing job.

Cedar wood roofing shingles are far more vulnerable to this kind of damage. Recommended treatment of these 40 year cedar shake roofing shingles winds up being so costly that few home owners will have their roof treated as they should.  Because of this it is rare to get a 20 year life span from their 40 year roof.  If they had gotten it treated as they should, in 40 years they would have spent more money than the cost of 2 new roofs, as well as the head-ache of finding competent workers to do this without causing more damage than the moss. That wood dry-rot and decay is really not a big problem, since the painted steel valley metal that is most always used will rarely last more than 20 years anyway.

It is just a shame that the owner had been fooled into paying so much more for that lame 20 year roof.  More than the cost of a good 40 year composite roof with copper valleys and flashing and even a custom copper ridge cap.

Clay & concrete roofing tiles

Tile roofs are resistant to wear and tear of the elements, depending on what it is made of.  There is a huge difference between the different roof tiles sold.  Tiles tend to grow moss and mildew more than most any other roofing, clogging up the gutter each year.  It looking quite unsightly. It can grow up under the overlapping shingle and crack them, causing substantial leaking that may be hard to spot and fix.  Clay tiles with a glazing on them are much less porous and are much more resistant to damage of this kind, but rare to see on a house.

The steel sheet-metal flashing and valley trays under the tiles are the biggest concern for this issue, and harder to access to clean out right.

Note: It is highly recommended to check this and hire a contractor to replace all the flashing with aluminum, lead, copper, or stainless steel. We recommend copper flashing.  A simple test can be preformed: magnet should not be able to stick to any of the rust free metals. If it is painted or zinc galvanized, it is not stainless steel.

There is nothing much to say on this subject, since you would be hard pressed to find a thatch here in the States, but the damage potential should be pretty obvious.

First off, most contractors do not carry the liability insurance and workman's comp that covers roofing.  This liability insurance is about 4 to 5 times as expensive as the other types of construction insurance. This has nothing to do with the dangerous nature of this work. That is what the Workman's Comprehensive Insurance is for.  If a worker falls off and gets hurt, they will not sue the homeowner if they have the proper Workman's Comp Insurance to protect them.  The liability insurance is to protect you incase the contractor or his workers screw up the roofing project and damage your house.  It seems that the roofers in this area have been doing such crappy work that they have accounted for 70 to 90% of all the claims processed by the CCB in Oregon.  This is one of the worst statistics you are likely to run across.  And that is even considering that many the homeowner are not able to act on their complaint within the first year. In many cases it is a moot point, since the CCB only requires a 1 year warranty by all licensed contractors.  Few homeowners will really check into the contractor's background for reported complaints, and check to see that they carry the proper insurance to cover roofing work.  Take the time, or you will be sorry.  Ask for a written warranty that is longer than one year.  There should be no reason that a reputable contractor would not be proud to write you a 20-year installation warranty, if they truly believe in their work.

To recap, insist on:

(a) No pressure washers to be used on your roof! Nothing stronger than a garden hose spraying downwards only. They need to use a hand scraper, or a wide hoe like scraper as described above, and carefully scrape the moss off.

(b) To fully clean up their mess and haul that debris away (no illegal dumps).

(c) A new custom copper roof cap is best to prevent further moss build-up.

(d) A moss control powder should be applied to kill the moss and mildew that was missed as well as the moss spores left behind.

(e) Get some leaf protection for your gutters (if you have them) to help minimize the traffic on your roof in the future.

E-mail DMR Gutters at (503) 351-7082 
for a free no-obligation estimate for the
finest in rain management.
(as long as you are local to the Portland Oregon metro area)

Below is a photo of our
Better Business Bureau's
NW Business Integrity Award
for the year 1998

We were also a 1997 finalist for this same award. See our referral web page to see how we managed to be honored with this special award