[TheForge] OT - Asphalt shingle rot? (Lichen)

[CGRAF]

You are right in that the asphalt/mineral composition will not in itself 
support the lichen.

There is some source of organic material. (leaves, bird debris, rotting 
wood etc)
The roof is also not drying out completely.
The roofing just provides a base to put it all together.

A light bleach should not do too much damage, however without 
eliminating either the water or the organics the lichen will be back.
Just keep in mind that the lichen isn't the problem it is the symptom.

There are commercially available zinc strips that are not too pricey and 
worth better than the galvanized, more zinc.
Copper will also work, but may take out the galvanized roofing nails.

Are there overhanging trees? More sunlight will help dry the roof.
What is the roof pitch? Some roofs are just too flat for shingles.When 
the roof lacks sufficient pitch water gets under the shingles more 
dragging organics along.The underside of the shingles remain wetter 
longer. Eventually this will take out the roof deck itself.


Mike Graf