Roof Cleaning especially composition roofs can be an expensive lesson if not done correctly. In the Northwest, specifically the Portland, Oregon area moss tends to grow thick and rather quickly most of the year. It seems like every year customers call us and say they had an explosion of moss growth. This is partly due to our mild and damp climate about 10 months out of the year we receive a rain. Moss tends to grow in areas with little sunlight, typically starting on the north side of homes and as it releases spores they germinate on other areas of the roof. Moss can start to grow in as little as 1 year on new composition roofs and often catch unsuspecting homeowners by surprise.
The most important thing to do if you suddenly notice a large amount of moss growing on your roof is not not panic. To many times homeowners think that moss needs to be removed right a way so their roof is instantly clean again. The truth is, once moss is established itself on the roof the best thing to do is research how to control moss and NOT damage the roofing material. Quickly ripping moss off the roof either by pressure washing or brushing moss with a wire brush can lead to massive granule loss as seen in the photo on the left. The dark area looks like mold, actually its missing granules!
What are common methods for roof cleaning?
What are the most common methods for roof cleaning? There is a variety of methods of roof cleaning depending on your budget and time constraints and roof type. After being in the roof cleaning 
business for almost 20 years I have seen many roofs damaged by pressure washing. Roof moss has roots (rhizoids) which attach to the roofing granules. If the moss is suddenly blasted off the roof, the granules also are blasted off the roof also. The roof granules play an intricate part in protecting your home from the elements. Some roof cleaning experts say pressure washing can remove as much as 10 years off the life of the roof. I would say that’s a fair assessment, if not a bit on the conservative side. Honestly, I have seen more roofs ruined by pressure washing than any other method.
Another widely used roof cleaning method is the use of a wire brush, this is very common in the Northwest to brush live moss off of the roof. When a person brushes the edges of the shingles with a wire brush they are in fact pushing the moss into and under the roofs edge. After the bulk of the moss is brushed off the roof, it is then typically treated to kill any residual moss that may have been left behind. The problem with roof cleaning via wire brushing, is the edges are now worn from the wire bristles. The moss that was pushed under the shingles will grow underneath lifting the shingles and exposing the roof to the elements within a year or so. The vicious cycle again repeats itself, but now the moss is growing not only on the edge of the shingle, but underneath. Each time wire brushing is used as a roof cleaning method the edges of the shingles take on more aggressive wear.
What is the best method for roof cleaning?
In my experience, treating the roof and allowing the moss to naturally weather off is the best method. Annual treatments keep the moss at bay, keep new moss from growing and causes virtually no wear to the material or environment. In Oregon, moss treatments are heavily regulated by the Department of Agriculture and any persons performing such a task needs to be licensed through the State of Oregon. While treating the roof does take longer for the moss to disappear, in the long run it will save your roof from being replace prematurely. There are many types of roof treatments on the market, and many types of delivery methods. We have been treating roofs for nearly 20 years and know which methods work well in the Northwest.
If you are under a certain time constraint, the next best method is to treat the moss and give it a couple months to fully die. Then once everything is dead, dry and crumbly remove some of the heavier moss in the drier months. This will still create some wear on the roofing material, but if customers don’t want to wait or can’t wait for moss to naturally wear off this is another alternative. We also provide a free roof inspection while we are on the property.
Our roof cleaning service area includes: Portland, Beaverton, Hillsboro, Tigard, Sherwood, Oregon