Moss Damage to Asphalt Roofing

Author: Pacific Northwest Inspections Group, LLC   Date: 23-Nov-2013.   Category: Roofing   Add to Favorites  The common site and wet winter climates is bright green moss growing unrest of both expensive and inexpensive homes here in the Seattle area. Thick Moss on shingled roof systems is particularly common in the State of Washington. While roof moss may seem to be just a cosmetic problem, if left in place it can severely damage your roof and even have disastrous consequences for other parts of your home. Moss is a plant that grows naturally on just about any surface including the ground, trees and sidewalks. During the moist cooler months the moss is dormant. Moss is different from algae,lichen or mold fungi which are typically easier to clean and less damaging to the roof.

Moss readily grows on asphalt and wood shingles especially in the space between the shingles with the sports collect and what comments Most commonly grows into a matt a few inches thick and once established it next like a sponge soaking up in-store and rainwater some of that water then wicks upunder the shingles through capillary action and soaks into and through the roof underlayment eventually saturating the roof sheeting below. Moss growth is usually the greatest on north facing roof or a roof area shaded by trees were solar drying his inhibited, the wet roof sheeting is preferred perfect for supporting mold growth and if the condition goes unchecked the sheathing ultimately decays and loses its structurally integrity - where the moisture content of the sheathing may exceed 30% - this defy spreads to the supporting restructure making the roof unsafe. 

This can even happen on roof systems that have attics with proper ventilation. It is painfully obvious that moss shortens the lifespan of the roof and can result in costly repairs, both structurally and cosmetic, that would not be necessary if the roof was maintained properly and kept clear of moss. One way of controlling moss is by installing Zinc or Copper flashing along the peak as rain washes down the roof some of the metal dissolves and kills the moss. If Moss has already started growing and it is best to carefully remove it with a brush her broom I recommend doing this on a regular basis typically once or twice a year I would avoid power washing the moss off because I can dry moisture under the shingles damaging the underlayment and roof components it should also be noted that some newer shingles have moss inhibitors don't think this bill and that will keep Moss at bay for up to 20 years. As you can seen in the image below copper is the preferred choice.