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[SEAOC] Re: [SEAOC] ridge vent in wood roof diaphragm[Subject Prev][Subject Next][Thread Prev][Thread Next]
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- Subject: [SEAOC] Re: [SEAOC] ridge vent in wood roof diaphragm
- From: Frank Woeste <fwoeste(--nospam--at)vt.edu>
- Date: Wed, 11 Sep 1996 18:18:02 +0600
Rick: Regarding question 1, in "post-frame" diaphragm design, we treat the two roof halves as two independent diaphragms. We assume that the chord forces are carried by the roof purlins. Regarding question 2, I do not understand the purpose of the blocking per UBC when no other code to my knowledge requires blocking between residential roof-truss bearing points. Some will probably say "transfer of chord forces", but we have learned in post-frame that simple models for chord forces are just that--simple. They are not realistic. If you research chord forces in residential roof trusses, I suspect that you could establish that the plywood sheathing is carrying the chord forces. Frank Woeste, P. E., Ph. D. 03:52 PM 9/11/96 -0400, you wrote: >On pitched (gabled) wood roofs using plywood sheathing over either >prefabricated wood trusses or stick-built rafter framing there quite >often is a continuous ridge vent, which requires a continuous opening >in the diaphragm a couple of inches wide along the ridgeline of the >roof. > >1. Does anyone have advice on how forces in the diaphragm are handled at >this opening? > >In conjunction with the ridge vent (for air flow out), there often are >continuous soffit vents (for air flow in) to provide the code-required >ventilation of the attic space. Blocking in the spaces between the >trusses for tranfer of diaphragm forces to the top plate unfortunately >blocks this air flow. > >2. Does anyone have advice on how these two conflicting requirements >(structural force transfer vs. architectural ventilation requirements) >can be handled? > >Rick Burch >Columbia, SC > >... > > Frank E. Woeste, Ph. D., P. E. Biological Systems Engineering Virginia Tech Blacksburg, VA 24061-0303 Home:(540)951-0469 Office:(540)231-6093 FAX:(540)231-3199 ...
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