From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
Date: Sun, 18 Apr 1999 23:41:54 -0400
First, make sure the tiles are *actually* lightweight! I can't recall a
contractor ever telling me that the tiles were not lightweight, yet, if I
take a tile and weigh it, it weighs the amount of a normal weight tile. One
tile that I have in the office measures 13" X 16.5" and weighs 10 pounds.
Considering the overlap, the installed weight of this tile alone would be
about 10 - 12 psf of sloping surface. Depending on your roof slope, the
weight per horizontal unit area would be more. If the tiles are chinked with
concrete, I would use 20 psf of sloping surface.
At one time, (1964 and possibly 1967) the UBC had material dead loads in it,
but removed it. I consider a minimum dead load of 10 psf per horizontal unit
area to be appropriate for the top chord. I think the plated truss industry
uses 10 psf as a minimum on the top chord and 10 psf total dead and live on
the bottom chord where the attic is accessible.
Don't let appearance of adequacy fool you. Remember that in the plated truss
industry the controlling factor usually is the connector, not the chords or
web members. If any tension connections have a 1" X 3" (or similar size)
plate, I would take a critical look at it.
A. Roger Turk, P.E.(Structural)
Dennis Wish wrote:
. > Apr 18, 1999 6:30 PM
. > --------------------------------
. > From the Offices
. > of Dennis S. Wish, PE
. > -----------
. > 1. To the best of anyones knowledge, is there a minimum roof dead load
. > called out in the UBC or BOCA codes for assume in residential design?
. > 2. Is there a minimum dead load to assume for the design of plated roof
. > trusses (Gang-nail type trusses) when used for residential design (like
. > 10 psf top chord and 10 psf bottom chord).
. > 3. What weight is assumed for Cedar Shake (Split shake and not shingle)?
. > Is this weight assumed to be dry weight or the weight of the shake when
. > wet?
. > I have to recommend if a client can change from a Shake roof (with
. > plywood sheathing) to a lightweight tile. Disregarding the effect of the
. > additional weight on lateral resistance (typically wind will control in
. > one direction, seismic in the other) I have inspected the roof trusses
. > which appear to be very well built and capable (by inspection) of at
. > least a 10 psf top chord load and a 10 psf ceiling load.
. > Although this is one of the easier professional opinions for me to make,
. > a recent post had me questioning if there is a minimum required dead load
. > to use as there appears to be if a Compo roof is used (3 layers).
. > Any opinions?
. > Thanks,
. > Dennis S. Wish, PE
. > Structural Engineering Consultant