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RE: Roof Truss Tie Downs

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While it’s preferred (from an engineering point of view) to install the hardware directly on the framing rather than over the sheathing, from a construction point of view it’s easier to install it over the sheathing. One reason is due to the fact that it’s hard to drive nails through the hardware when attaching the sheathing. I know that the hurricane straps are smaller than, say coil straps, but the difficulty is still there. The Simpson literature illustrates straps installed over sheathing, which I think is O.K. I just won’t do it at the foundation (at a PA strap) because of the eccentricity.

 

Hmmm…also in the Simpson catalog is a note (on page 142, 2005 edition) which says “Hurricane Ties do not replace solid blocking”. This addresses another recent thread.

 

My practice with respect to installing hardware is to install it over the sheathing wherever possible, even if the capacity of the connector is reduced. For straps, I considered reducing the capacity until I realized that G was the same for the sheathing as it is for the lumber I specify (Struct I sheathing and DF-L lumber). I’ve also seen A34Fs, oops, I mean LTP4s installed as shear transfer between the blocking and top plate where they are installed over wall sheathing. Personally, I don’t specify wall sheathing over the blocking, but it might end up that way to provide a flat surface all the way to the underside of the rafters.

 

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: David Maynard [mailto:davemaynard(--nospam--at)ceincorp.com]
Sent: Thursday, April 14, 2005 2:12 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Roof Truss Tie Downs

 

Brian,

 

Try this on for size.  Found in the "Important Information & General Notes" section of the Simpson Strong Tie Wood Construction Connectors-2005 catalog, under "Instructions for the Installer", item c. states (page 11):

"Install all specified fasteners before loading the connection."

 

I think that just about covers it.  Gotta put the hurricane clip on first before putting on the roof sheeting.  This makes perfect sense to me.  Then again, what do I know?  I'm just an engineer.  *smile*

 

Dave Maynard, PE

Gillette, Wyoming

-----Original Message-----
From: Brian Hsi [mailto:bsh(--nospam--at)rath-goss.com]
Sent: Thursday, April 14, 2005 2:53 PM
To: seaint(--nospam--at)seaint.org
Subject: Roof Truss Tie Downs

Hi all!

 

I think I have a simple question, but then again…maybe it’s not that simple.  Can someone please inform me if there is literature or a code that requires the installation of roof truss tie-downs or hurricane clips prior to the installation of the roof sheathing?  I figure it’s a “no brainer” and common sense tells you that you need to tie the trusses down before you attach the component that will cause the uplift on the truss.  I would appreciate if anyone could point to specific literature stating this.  Or, let me know if I’m “out to lunch” on this one.

 

Thanks!

 

Brian Hsi, P.E.