Methods of Roof Moss Removal in Seattle

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Over 10,000 roofs are replaced per year due to water intrusion, in the Seattle area. Roof Moss is a major contributing factor to the number of roof replacements. Moss grows in patches 1-3 inches wide. Homes with infrequent sunlight or under foliage are the most prone to moss growth. Large patches of moss trapping moisture in 1-3 inch mats create water dams that then begin pushing water underneath roofing substrate. The roofing material is never left to dry out.The consequences are:

  • Rot.
  • Mildew
  • Buckling

What is Roof Mold?

Bryophytes are soft plants that grow in mats and clumps. They reproduce through periodic release of airborne spores. They have no vascular system to feed themselves as plants with roots do. Bryophytes therefore grow where moisture is prevalent. The Seattle region with between 72-88 days of sunshine a year is an inviting environment for moss growth. Our lack of sun is the reason moss grows so heavily in the area. With no ability to control our amount of sunshine, we are left to do periodic maintenance.

Differing Methods of Moss Control

You can speak to any 2 roof cleaners in the country and the proper method for roof cleaning and moss control is always up for debate. There are standard methods of moss control practiced around the country these methods are:

  • Power washing to remove moss.
  • The use of zinc strips.
  • Chemical treatment.

Power Washing 

Pressure washing without adequate chemical treatment afterwards is the least effective method in killing moss. Without the use of a moss inhibiting chemical you’re left with a roof that will need another cleaning almost immediately. There have been several studies done on the damage a power washer can do to asphalt granules.  ARMA [Asphalt Roofing Manufactures Association] recommends not using a pressure washer on asphalt shingles for roof moss removal. Their primary concern is the loss of granules. Although not as good on asphalt shingles, a power-washing is probably the only effective way of properly cleaning cedar and metal roofs.

The metal roofing vent prevents moss growth.

Zinc Strips

Zinc Strips are effective means of containing moss growth. Due to the cost and the amount of coverage required to kill moss, many times it is unfeasible to use this method. For Zinc strips to successfully control moss growth they must be placed every 3 feet from the tip of the roof to the gutter line. This method is very unsightly and many homeowners do not like the look of Zinc strips going down their entire roof line. The picture above shows CLEARLY, that zinc and metal DO stop moss from growing. Where the metal vents are present; no moss is growing directly beneath them.

To effectively use zinc strips:

  1. Two inches of zinc should protrude the asphalt shingle.
  2. They should start at the ridge cap and end 3 feet above the gutter.

Chemical Treatment of Moss

Chemical treatment, also called soft wash roof cleaning, in our opinion, is the most effective means of moss control. Using the right chemicals, completely kills all moss spores and prevents new moss from rebuilding. Most soft wash roof cleaner’s offer warranties of 1-5 years, they are secure in offering these warranties because they know that it took years for this moss to grow on your roof and it will take years for it to grow back, provided the right chemicals are used in strong enough doses.

The decision on what method is the right method for roof cleaning in Seattle is always up for debate. PWNG uses the chemical soft washing method to soundly control moss. We stand by our service and offer a 1-year warranty with every roof cleaning in Seattle. We look forward to any comments or questions our readers might have and we welcome an open discussion on roof cleaning.

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