fire retarding plywood identificationproblems

huangyhg

fire retarding plywood identification/problems
hello,
we are looking at a set of townhomes that is being re-roofed.  as the roofer was removing the shingles they noticed the roof sheathing was very soft and aactually broke threw.  the sheathing is supposed to be frt plywood, but i can't seem to find anything on the grade stamp that confirms this.  how can i tell if this is frt plywood?  has anyone else dealt with the problems that were associated with frt plywood made in the 80's and 90's?  thanks!
here is a pic of the grade stamp.
if i re  
check the underside of the plywood.  might be there.
btw - if it is frt - then you might have to replace all of it.

yeah miketheengineer is right.  i was involved with a re-roof a while back - the frt was falling apart.  i could just grab a handfull of fibers.  we replaced 30% or so and went over all with a new layer of plywood.  lots of info on the web.  it seems like they have got it fixed but....
the piece just to the right in your first picture appears to be different than the other.  lighter in color, and looks like particleboard.  some of the sheathing may have been replaced already.
my guess is the frt is only a 4' section on either side of a fire barrier.
don phillips