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RE: Proposed roof design

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Bill,

I did a roof similar to that that had exposed timber framed trusses but not
in zone 4 and with fairly light lateral loads.  It had 2x8 purlins spanning
between the trusses with the space between the purlins insulated, then 2x4
sleepers laid flat on top of the purlins (to form an air space to vent the
roof) and the plywood deck on top.  I called for full depth 2x10 blocking to
be installed between the purlins immediately above the trusses and
transferred all my in plane loads thru this blocking.  The purlins were also
design for the biaxial bending if I remember correctly.  The big thing is
being on site when they start constructing the roof so you can emphasize the
importance of how everything gets put together then oversee the first
section or two.

Troy A. Madlem, P.E.
mailto:tmadlem(--nospam--at)kenherceg.com



 -----Original Message-----
From: 	Bill Allen [mailto:T.W.Allen(--nospam--at)cox.net] 
Sent:	Wednesday, October 01, 2003 3:07 PM
To:	seaint(--nospam--at)seaint.org
Subject:	Proposed roof design

Ladies and Gentlemen;

An architectural client of mine is proposing an unorthodox (to me) roof
design and has asked me to review. I have some concerns, but I thought I
would solicit comments from the engineering community before I
responded.

When he first described the system to me, I thought the sheathing would
be applied directly on the roof rafters.

See: http://members.cox.net/ballense/roof.htm

Criteria:

UBC/CBC 70 MPH Wind, Exposure C
Seismic Zone 4 (although residential construction and diaphragm shears
should be small < 150 PLF).

Your comments would be most appreciated.

Thanks,

T. William (Bill) Allen, S.E. (CA #2607)
V/F (949) 248-8588
San Juan Capistrano, CA
http://members.cox.net/ballense/




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