Lateral restraint on load bearing gable walls

[brudgers]

See Figure 52 on Page 42 here:http://www.awc.org/pdf/WCD1-300.pdf

Maybe the problem is we see so little "conventional wood frame construction"?

Note that the subflooring turns the ceiling into a diaphragm and ties the walls together.

Subflooring in the attic is not really typical practice, even though the framing is conventional.

 

[Yankee]

And note the metal straps which share the load to more than the one ceiling joist. Attic subfloor is common around here and changes the nature of our discussion as brudgers points out.

 

[TJacobs]

Note that the subflooring turns the ceiling into a diaphragm and ties the walls together.Subflooring in the attic is not really typical practice, even though the framing is conventional.

Correct. You could possibly accomplish the same thing with rafter ties every 4th rafter on top of the ceiling joists in accordance with R802.3.1.

My point is I could show the WFCM detail to the builder without getting an engineer involved, builder's choice.

 

[Yankee]

Correct. You could possibly accomplish the same thing with rafter ties every 4th rafter on top of the ceiling joists in accordance with R802.3.1.My point is I could show the WFCM detail to the builder without getting an engineer involved, builder's choice.

How did you determine the every 4th rafter spacing?

 

[TJacobs]

How did you determine the every 4th rafter spacing?

Oops...past practice. 1998 IOTFDC (our previous code):

802.3 Framing details.

Rafters shall be nailed to ceiling joists to form a continuous tie between exterior walls where joists are parallel to the rafters. Where not parallel, rafters shall be tied with a rafter tie, located as near the plate as practical. Rafter ties shall be spaced not more than 4 feet (1219 mm) on center. Rafters shall be framed to ridge board or to each other with gusset plate as a tie. Ridge board shall be at least 1-inch (25.4 mm) nominal thickness and not less in depth than the cut end of the rafter. At all valleys and hips there shall be a valley or hip rafter not less than 2-inch (51 mm) nominal thickness and not less in depth than the cut end of the rafter. Hip and valley rafters shall be supported at the ridge by a brace to a load-bearing partition or be designed to carry and distribute the specific load at that point.

That is not in the 2006 IRC...my bad! However, it WAS good enough in 1998. Thanks for the catch.

BTW, there is a definition for rafter tie in the WFCM.

 

[brudgers]

Correct. You could possibly accomplish the same thing with rafter ties every 4th rafter on top of the ceiling joists in accordance with R802.3.1.My point is I could show the WFCM detail to the builder without getting an engineer involved, builder's choice.

Using ties every fourth rafter isn't the same thing, because the non-triangulated rafter are bearing at the ridge and placing thrust on the top of the wall.

In the diagram, all every rafter pair is fully triangulated by the floor diaphragm so it doesn't matter which way the joists run.