Dennis S. Wish PE
Thanks for the comments about roof loads and minimum dead loads. Roger Turk's
comments were pretty much dead on to what I was looking for. As far as
replacment weight - I restricted the roof to a 6.0 psf tile and required the
contractor to provide an approriate ICBO report from the manufacturer of the
tile to verify the weight before installation.
Regardless of the Shake weight, the lightweigt tile (6 psf) and the existing
1/2" thk plwd (and builders paper) would not exceed 10 psf at the top chord.
I had read someplace that the weight of green shake is typically used in the
design dead load and that this can very from 3.0 to 5.5 psf.
Roger, you brought up the plates used on the trusses - a very good point. I
did inspect them and found them all to be no less than 6x6 oversized press
plates. I'm not sure how much they were used in the early 70's but do know
that they are more the standard now. They could have been nailed plates, but
my eyes are not what they were and I could not make out the nail heads.
Even though I posted this questions, I have had to deal with this issue for
years. I've always considered my alternatives to be conservative and when the
truss looks particularly flimsy, I'll recommend analysis of the truss or
replacement with a similar weight material regardless of appearance.
Thanks again for all the help,