Roof Rafter Creating Attic Ceiling

[Calatrav]

I have project where the customer is wanting the roof rafters to create the second floor ceiling so like a vaulted ceiling I typically recommend a structural ridge but in this case it’s a 70’-0” span. My question is if I can use a ridge board with cs16 straps over the top side of the rafters in place of collar ties and hurricane ties strong enough to resist the outthrust, if this should suffice or am I missing something? I’ve attached the ceiling layout in gray with red lines for ceiling profile and roof layout.

 

[jayrod12]

Connecting the rafters to the outside walls to transfer the thrust loads to the walls is only step 1.

Step 2: figure out where the wall is going to transfer the thrust load to. Usually it would be the ceiling joists, but you don't have those in a vaulted ceiling application. You need something to eliminate, or absorb the thrust. Whether that is tension ties at a regular spacing, or a ridge beam with some intermediate posts, or something else, that's up to you. I'm not sure what would work best in your specific scenario.

 

[phamENG]

Can we get a section? Based on the plan, it looks like your rafters frame into the top of the first floor walls at the same elevation as the floor joists. At least that's what I get from the "dead space" on plan between dormers that looks like it's partitioned off with a kneewall.

If that's the case, it's easy - your floor joists resist the thrust. But I'm guessing I'm missing something since you're asking the question...

 

[jayrod12]

Based on the plan, it looks like your rafters frame into the top of the first floor walls at the same elevation as the floor joists. At least that's what I get from the "dead space" on plan between dormers that looks like it's partitioned off with a kneewall.

Good catch. Although I only see that on the left half. The rest of it appears to be fully open.

Although if they are partial height walls that are balloon framed from the second floor, you may be able to make a go of using the studs as cantilever studs that take the thrust loads down to the floor framing.

A section would surely help.