Jim

attic ventilation is a complicated issue. i run a lab in MI that tests
and id's mold in homes, attics, other (as well as lots of other things
too). if you are getting mold growth on your roofing boards and the
joists without leaking, you are having humidity accumulation, i.e.
condensation. if the mold growth is active, green and fuzzy, the
problem is a current issue. if the growth is thin and black and looks
like charcoal, the issue is most likely a different season, as this is
the 'dormant' stage of mold growth. you've got to understand that
condensation occurs when temperatures change faster than the humidity.
increasing ventilation allows the excess moisture to escape the attic
during air flow (created by temp differentials, pressure diffs, etc)
before it can condense. increase ventilation - using fan force if
necessary - decrease reoccurance of condensation. other things... make
sure bathrooms, dryers, and sewer vent are not directed into your
attic - ever! many homes i am called to have these venting into the
attic. very stupid. also if the mold is fine black dry stuff and it
gets wet, it can bloom very fast damaging wood and causing serious
allergy effects on people even if you dont have allergies... yet...if
you clean this stuff up ( and u should if there is lots of area with
growth) dont use bleach, use quaternary ammonium compounds in a
detergent (read labels!) dont drip (catch it all), dry it thoroughly,
make sure insulation is DRY!!! good luck