Replies

1. 
   junkhound | Apr 19, 2013 03:07pm | #1

   This is Puget Sound moss (Renton)

   View Image

    

   Part of the local culture.  Some folks cut down all their trees, that eliminates a lot of Moss.  After 10-15 years, it is thick enough you can just peel it off like lifting carpet. Roof shown is 35 years old, no leaks yet (<G>)

    

   Have pressure washed my roof (not this particular one), you just need to be careful to not dig a hole in the asphalt.  Cedar shake roofs get PW all the time around here, and then replaced with metal or asphalt after about 20 years, with or without PW.   

2. 
   DanH | Apr 19, 2013 07:41pm | #2

   You can use specialized chemicals, or plain old chlorine bleach (the bleach must be FRESH, and only diluted maybe 50/50).  With most of these chemicals (certainly the bleach) you need to somehow prevent the stuff from getting on plantings around the house (at least those that you aren't planning to replace).

   Pressure washing is risky.  Depends on the condition of the roof and how much pressure you use.  (Note that for moss to get a foothold usually the shingles (if asphalt) must already be beginning to break down.)

   A more or less permanent "fix" is to install copper or zinc strips along the ridge and maybe every few rows down.  This is very effective for algae, but not quite as effective for moss.  Shingles that contain copper or zinc are also at least moderately effective.

1. 
   junkhound | Apr 20, 2013 12:27am | #3

   for moss to get a foothold usually the shingles (if asphalt) must already be beginning to break down

   Since the OP in on Puget Sound, best to qualify that:  probably true in climates where it freezes a lot (aka MN?), but here in PNW west of cascades moss will grow on even galvanized sheet and glass if there are enough fir needles fall and not removed within a few weeks.  Skylights need cleaning at least every season if the house is near any DF trees. Also, the alder pollen sticks like hot melt adhesive  which is a whloe 'nuther story.   At least the maple leaves here are so big that they don't get into gutter.

   Heck, I've even had alder trees start in galvanized gutters over the course of one winter.  Like implied, cutting down all trees within 300 feet prevents that which is what most of the developers do nowadays, cut down all the trees. 

3. 
   crosscountry | Apr 21, 2013 11:56pm | #4

   zinc & moss

   After you clean your roof (I pressure washed and it worked fine...but it was just a shed), and before you cut down trees...try putting some zinc strips under the top row of shingles. Its kept my roof moss free for years.