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RE: Roof to top plate connection?

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Paul-

 

If I’m visualizing the connection correctly, there’s “no way” I would accept it because I don’t believe there’s an adequate shear transfer mechanism. First of all, there’s no boundary nailing. Secondly, to transfer the load from the sheathing to the top plate, the joists must go into cross grain bending (over 1-1/2”) then into bearing onto the short blocking. Again, if I’m visualizing the connection correctly, the “hurricane ties” at attached to the bottom of the joist, not at the top of the blocking. If the goal of the contractor was to provide ventilation, I would be more receptive to a vertical slot of equal area. That way, short blocks would still provide boundary nailing.

 

An unblocked diaphragm does not have blocking at panel joints in the field (the “field” being the region within the boundaries), and is not referring to the condition at the boundaries.

 

I say “stand firm”.

 

T. William (Bill) Allen, S.E. (CA #2607)

ALLEN DESIGNS

Consulting Structural Engineers

http://www.AllenDesigns.com

V (949) 248-8588

F (949) 209-2509

 

-----Original Message-----
From: Paul Skidmore [mailto:paul(--nospam--at)psarchitecture.com]
Sent: Friday, April 08, 2005 11:20 PM
To: seaint(--nospam--at)seaint.org
Subject: Roof to top plate connection?

 

Hello All--

 

Using the allowable plywood shear capacities for horizontal diaphragms from IBC 2003. The drawings called for full depth blocking at the interface between roof sheathing and top plate. In this case, the contractor left an 1-1/2 air gap between the underside of the sheathing and the blocking. The joists themselves are 2x12. Of course required edge nailing was not achieved. The lateral loads are quite minimal--unblocked diaphragm is more than acceptable.

 

I have always called for full depth blocking in this condition, but now I'm getting some conflicting information, i.e. that since the testing was for an unblocked diaphragm, this condition will still develop the full lateral capacity noted in the IBC table--as long as an alternate method of transfering the lateral load into the top plate is provided. In this case, the "hurricane ties" supply adequate lateral capacity.

 

 

This situation causes me some concern, but I'm being overruled by higher-ups. But then, I wonder if I'm too reliant on academic sources, and not being flexible enough in my thinking.  In the past I've always required additional blocking to "fill the gap", using A34's or A35's  with screws into the underside of the sheathing as necessary to maintain a continuous load path. I'm wondering what the list thinks?

 

Thanks.

 

Paul Skidmore