Our Condo Association is in the process of reviewing bids to have our units
reshingled
with 30-year fiberglass (GAF or Tamko) over a single layer of shingles. One
of the
bidders strongly suggested that we strip the existing shingles first,
claiming that if we
didn't we would decrease the useful life of the new shingles by as much as
50%! Other
people I've spoken to say that 2-4 years is more likely.

Obviously we would like to avoid the additional cost of removing the
shingles but not if
it means we would only get 15 years out of the new shingles. Can anyone
provide more
insight as to the actual impact of NOT stripping first?

Thanks in advance, Jeff R.

--- Other Info ---
We are in the Midwest.
Believe the existing shingles are asphalt organic felt (does this matter?)
Some of the existing shingles have started to curl slightly.