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Re: to block or not to block?

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Hi Joe,
 
Actually this is kind of a rhetorical question for the list.  It's not my design, so I have no Idea what the nailing is. Your point about the strapping is a good one and in my slack time the last couple of days since I saw this construction (from afar as they say) I actually thought about it myself.  Seems it would be a good thing for chord forces in the roof diaphragm.  I have also called out on projects what you are calling truss blocks, although at times I have used a "diagonal braced" panel to be manufactured by the truss manufacturer and located between the truss ends.  I'll show the shear load required to be transferred from the room to the double plate at the wall.  That way the plywood and nailing is not a worry.  Also, if the insulation is held down at the wall, venting can be provided through the plywood covering without a possible decrease of shear transfer capability of the panel.  On the other hand due some other detailing issues that I have found in my new location (desert southwest), where roof trusses are fabricated with a vertical member at the bearing points that protrudes above the roof plane (to provide a parapet), things get quite congested trying to get diaphragm loads transferred to the ends of the trusses then into the wall.  This method that I have proposed would clean things up a little.  Mind you, I don't know if at this particular house cleaning up details was on anyone's mind (since I doubt the house had any engineering input), or if the contractor just thought it was cheaper or whatever.  It just struck me as a possibility.  We have wind design here, but in general not anything too awful to design for.  At least at that location of a residence since the plf shear values tend to be manageable.  to get things into a small shear wall panel within a long window wall is usually where the brain needs to start really working.
 
Anyway, thanks for yours and the input from all others as well
Joseph R. Grill, PE
----- Original Message -----
Sent: Thursday, November 04, 2004 6:24 PM
Subject: Re: to block or not to block?

Joe:
 
Is the roof nailing 8d's or 10d's @ 6"oc ? Wall nailing 8d's @ 6"oc. If you have a 2x at that block the nail plane will be crossing each other. A 3x will be better (there will be wood around the nails). Yes the contractor will wine and yell and whatever. So what !
 
Even though it is low end quality I believe it is more of an integrity issue with the connection.
 
Also, in that situation we require a CS 16 full length of wall on the vertical plywood face and we use the strap nailing as our edge nailing.
 
On moderate quality we may install what we call truss blocks between the trusses. That is a rectangular panel with 2x4's verts and bottom and 3x4 or 6 at top with 3/8" OSB or Plywd.
 
We are in a high seismic area however many times wind governs shear wall design in most houses, because the roofs are not that large.
 
Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA