Rafter to exterior wall connection

[Tony1985]

Do hurricane clips replace the need for tension ties when rafters rest on top of exterior wall top plates and attic floor joists run perpendicular to the rafters?

 

[CELinOttawa]

Depends on the calculation - Is this a ridge beam or ridge board system?

As a P.Eng. you can use any system you can show will work, so possibly is the correct answer.

 

[Tony1985]

Ridge board - hoping to get the architecturals (does not seem to have been "engineered") to review. Hoping that some thought went into it.

 

[XR250]

They are only designed for up and down load, not push out. What is keeping that wall tied back to the floor diaphragm?

 

[Tony1985]

I did not see anything method of later supported - I have requested the drawings, though my initial recommendation was that tension ties would have to be installed. Got flack from the owner about "...the town approved the installation..." (how many times have we heard that one? ).

 

[Tony1985]

oops - meant to write "lateral" not "later" support

 

[CELinOttawa]

Hurricane ties CAN take thrust... See the attached.

http://www.strongtie.com/products/connectors/h.asp#

Again, this depends on the design and what the thrust is. With a ridge board, I doubt it will work, but you cannot say that "by inspection"...

 

[CELinOttawa]

To be clear, it does depend on the type of hurricane tie... Excel may be right, but from the photo they look like the Zmax from Simpson (or very similar) which are capable in thrust.

 

[nac521]

Yes, most have out of plane load capacity, minimal though, and it puts the nails from the hurricane tie to the plate in constant withdrawal, which is not ideal. I would add another tie (or multiple ties depending on the amount of thrust) to the opposite side of the plate to rafter and verify the attic floor joists to wall connection is adequate to resist the thrust load. Follow the load path. Keep in mind the load values in the Simpson tables are increased for wind load duration for hurricane ties; you would need to reduce the values appropriately. Another option would be to remove some of the plywood flooring and add diagonal 2x_ kickers to get the load directly in the the attic floor joists if they align.

 

[woodman88]

In similar conditions I have used Simpson A34/A35 nailed to the top of the top plate and the side of the rafter at "x" o.c. to resist the horizontal load. As nac521 states, the ties as shown in the picture, placing the nails in constant withdraw is not something I would like to do.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[XR250]

I stand corrected - sort of. The F2 values are pretty small in most cases, however. I would count on other means to resist the thrust rather than fastener withdrawal -as NAC51 says. It is my experience that the it is the constant outward thrust caused by gravity loads that works the fasteners loose in tension over time - not the short duration stuff.

 

[CELinOttawa]

Quite right Excel, the loads must be low to make it work. That said there are many installs (particularly with long rafters) where this resistance actually matters...

 

[Jerehmy]

This wall is going to kick out. Are they using the ends of the 2x4's to frame the subflooring on top of? That's what it looks like. I wonder if connecting the floor diaphragm to those 2x4's would be enough to keep the wall in check. Those studs seem to be at 12" OC. 1 nail per stud but the end grain factor significantly reduces the capacity.

 

[CELinOttawa]

Jerehmy: That depends on the full job, ie interior walls, top plate to diaphragm connections, etc.

Pretty hard to comment on that level of detail without the full set of plans.

 

[Jerehmy]

CEL

Yeah. It still makes your scratch your head and wonder why they would ever frame the joists in the opposite direction. I'm curious more than anything. Keep us updated Tony!

 

[CELinOttawa]

Jerehmy: Ignorance. Not meaning it to be derogatory, they simply do not know.

 

[a2mfk]

I am helping my friend right now strengthen his roof that was built with conventional framing and no ridge beam, no thought to horizontal thrust- no bottom chords, nothing. He is having problems with roof movements. Built in 1999 in a small town in GA with plans that looks like they may have been a high school drafting project.

Make sure this gets done right- don't count on things to just "work". It looks like maybe you can use the plywood sheathing for a diaphragm if it is continuous?

 

[Tony1985]

Will keep you posted - have not been provided with the drawings yet (the review was part of a due-diligence process for someone purchasing a home). Not even sure if the client is buying the home anymore.