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Re: wood diaphragm edge / roof venting

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I don't agree that a pitched roof diaphragm with a ridge is no different than an
unblocked diaphragm. There are *two* discontinuities at the ridge; one for the
sheathing edge joint, and also the framing (rafter or truss chords) are jointed
at this location. There is shear force parallel to the ridge which is greatest
at the ends of the diaphragm, and linearly reduce to the midspan of the
diaphragm. There may need to be a formed sheet metal shear strip stapled to the
sheathing on each side of the ridge, when the shear force exceeds about 100
lb/ft. (engineered design, not prescriptive conventional construction).

For continuous ridge vent applications, suggest doing the same thing at the
ridge as suggested at the eaves. Namely, sheathe and apply strips (or solid
blocking at ridge) in every other framing bay, to develop required shear force
which would be double the regular force if the full length of sheathing/blocking
was used. Then the ventilated areas can be cut into the sheathing at the bays
where there is no diaphragm shear transfer at the ridge.

John Rose/APA

Paul Feather wrote:

> Paul Franceschi wrote:
>
>   A  continuous ridge vent is not an option because it would cause a
> diaphragm
>    discontinuity.
>
> This is only the case for a blocked diaphragm.  The joint at the ridge is no
> different from the joint along all the other panel edges for an unblocked
> diaphragm.  For residential construction where the diaphragm shears are low,
> continuous ridge vents can be detailed effectively.
>
> Paul Feather
>