I have Moss all over my Roof! Now what?

Moss is very common in this area. Moss and algea grow mostly in areas of low light and high moisture. Low light and high moisture pretty well describes most of the western Pacific Northwest and the wintertime.  Some of the most common ways to treat and maintain your roof are listed below.

One of the areas that moss is a concern on homes in this area our roofs. Depending on the roofs exposure moss can grow most of the year.  If sections of your home’s roof are shaded throughout the day and stay moist these are likely areas to grow moss.

Over time moss can damage your shingles if left un-checked. As the moss develops into a larger and larger colony more and more moisture is held against your roof. The colonies will also develop root systems that will dig in to the surface fibers on your shingles. As the colonies grow larger, they can actually lift the edges of the shingles. This can leave the shingles vulnerable to wind damage.

There are lots of ways to kill moss. Most of the good techniques involve some sort of the heavy metal application usually copper or zinc. Some really bad ideas involve laundry detergent and or power washers…..

In general the more trees you have around your house in the steeper your roof the more applications of moss killer you’ll need.

1.  The best way to control moss is with an annual or biannual application of a powdered or liquid name brand moss killer designed for roofs. For steep roofs I have found a hose end attached shrub and tree sprayer to be a handy tool.

moss out for roofs Shrub and tree sprayer for application of roof moss killer











2. Another option for continuous moss control are some new

shingles that are actually impregnated with copper

granules. I have only seen the shingles used on two

different roofs and the major issue with these is the fact that

the ridge shingles were not impregnated in a still need to be

treated for moss/algae growth.

Moss growth on Keizer Oregon ridge shingles












3. Mechanically removing the moss is also an option.

This option is really only for the very worst conditions.

It envolves a paint scraper, screwdriver, putty knife or

something similar and trecking across your roof slope and very

carefully removing the moss growth.

This technique is very prone to damage of the asphalt

composition shingles and should be used as a last resort.

Moss on a Salem, Oregon home














4. Zinc or Copper strips- These may be ok for preventing

algea growth but moss looks at the little strips and laughs.

You may have noticed some homes around town that have

clear sections of shingles under metal roof vents.

roof moss killed by zinc in Silverton, OregonWhat is going

on here is the

zinc in the

galvanized steel

is leaching on to

the roof every

time it rains.

This has lead to

people thinking that they could install little strips or even

sections of wire to kill moss and algea, but this is not

usually an effective technique.The difference is all

about-surface area.The roof vents have a rather large

amount of exposed surface and therefore a good amount

of rain hits the vents. Compare this situation to a 2 inch

wide strip of zinc and you

can see that there will be far less leaching occurring off

of the little strips.The strips usually are effective for 2 to 3 feet,

and I have seen the strips added every 2 or 3 feet down

an entire roof slope. This installation appeared to be

effective but I have only seen this once.

zinc moss strips











5.  Power washing, scraping with brooms, or laundry detergent. Unfortunantly I see the aftermath of these steps to control roof moss on far too many Salem area home inspections. If you are reading this post you probably have educated yourself enough to know that blasting or scraping the surface off of your aspahlt composite roof is a bad idea.  The folks that commit these heinous crimes are usually the people that already know-it-all and they maintain their homes the way they see fit.

-There may be some contractors who use power washers to clean roofs, but these individuals are licensed and bonded and have the experience to know which nozzle to use and how far to hold it away from the roof surface. Power washing should be strictly limited to the driveway and walkways surfaces around your home.

-Brooms and other mechanical abrasion are also techniques that should either be left on the ground or for qualified professional contractors. The removal of the surface granules on the asphalt shingle also removes the ultraviolet resistance and of the shingles.

-Laundry detergent, although will kill moss on your roof, is full of degreasers. An asphalt based composite shingle is a petroleum based grease compound. Do not put degreasers on your greasy roof.  (Thanks Joe Ocilia for educating me on this fact!)

Those are my 2¢ on how to control moss. Being a Salem, Oregon home inspector, I get the chance to see various maintenance techniques. By far the best one to use is the first one, which is a chemical, powdered or liquid, commercially available moss killer applied at annually or biannually.


  1. Do you have any evidence to back up the theory that laundry soap damages asphalt roofs? People have been doing this for decades and only recently have I heard that it is a problem.

    1. Yes I do Don. I have seen large chunks deteriorate from the surface of comp shingles after laundry detergent was applied. Most of the time the soap doesn’t sit on the surface very long and the damage that can be noticed is subtle. If you accelerate the deterioration the surface of your 30-year roof by 4-5 years you usually won’t be able to notice this until the roofing is at the end of its life.

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