2009 IRC - ICF Wall Construction

[XR250]

Figure R611.9(9) shows a roof truss fastened to the top of an ICF wall. The detail requires tension ties, roof boundary nailing and other stuff well in excess of what they require for a truss on top of a wood framed wall. Why the difference? I called our state code officials and they have no idea why.
FWIW, we are exempt from seismic design for residential structures in NC.

Thanks in advance.

 

[AELLC]

Because it is concrete wall and wood roof. Same as masonry wall to wood roof. Makes no difference whether seismic or non-seismic.

I would not feel comfortable living in a concrete-walled structure in a hurricane region knowing there is not good connx between roof and walls.

 

[XR250]

Are you worried about the wall falling on you? It seems less likely to fall as it has some cantilever effect from the footing and the ability to span horizontally better than a wood wall.

 

[AELLC]

OK, be that way. At least provide the equivalent of H2.5 tie at each roof truss.

 

[AELLC]

Isn't NC hurricane and tornado-prone? I don't understand why IRC.

 

[CBSE]

I've been doing ICF for a few years now. Calc your out of plane wall seismic force (and wind force) and design your tension tie to transfer this into the roof diaphragm. Really isn't too much different than wood requirements, only concrete ways more

 

[AELLC]

Minimum boundary nailing is 8d @ 6" oc, so you need at least that anyway. I just don't use the word boundary to construction types - they prefer the word "edge"...of course that doesn't define exactly what we engrs are referring to.

 

[XR250]

IRC does not require boundary nailing on wood structures AFAIK. They only require blocking between the trusses or rafters when the depth exceeds a certain amount. No blocking = no boundary nailing.
So back to my original question, "why would ICF construction be any different?"

 

[AELLC]

IRC doesn't require boundary nailing?

Then how do you nail the perimeter of the roof deck?