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[SEAOC] RE: [SEAOC] ridge vent in wood roof diaphragm

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When you calculate the actual openings that are required, you will find that 
a drilled hole is adequate for proper ventilation.  Connect the sheathing to 
the ridge and to the blocking at the perimeter walls.  Drill a hole just 
outside of the ridge and through the solid blocking at the perimeter wall. 
  Or place the perimeter wall blocking between alternate roof joists.

A hole size of about 1 or 1 1/2" diameter will often be sufficient without 
significantly altering the diaphragm capacity.

Harold Sprague
Black & Veatch
From: seaoc
To: seaoc(--nospam--at)
Subject: [SEAOC] ridge vent in wood roof diaphragm
Date: Wednesday, September 11, 1996 3:52PM

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

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