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

[CGRAF]

Sometimes in the rush to solve one problem we create others.

I have seen steel nails rusted out because of the galvanic reaction 
caused by water washing off of copper flashing.
  While the copper strips will kill lichen etc and probably not do any 
damage to the nails if the roof is steep enough, a flatter roof will 
have problems.
On a steep roof the nails rarely , if ever, get wet. On a flatter roof 
the wet zone is larger as the water move sideways more.

Lift a shingle and check the V made by the dust/water line. Are the 
nails on the dry side (inside) of the V?

Mike Graf