Need some help

[BrianHa]

I have a client wanting to do something I am afraid will not work. Doing a one story home, 63'-0 width x 39'-0 depth with a 6:12 gable roof, with a semi vaulted ceiling. The exterior walls at 8'-0 and in the interior walls at 10'-0. The vault follows the rafters till 10'-0. I am designing for 90 mph winds, 15 lbs psf contruction load and a dead load of 15 lbs psf on the roof. Based of the NDS span tables (my rafter span is 19'-6) I am using a 2x10 rafter. My celing joist span will be from the furthest rafter to an interior wall @ 20'-0 allowing me to use 2x10 ceiling joists. My fear is since the ceiling joist do not tie into the exterior wall, (they will be lag bolted with two 3/8' lags into the rafter), the loading of the roof will tend to push the exterior walls out. I have a total tributary width of 19'-6 at the ridge board. I have considered a ridge beam to alleviate some of the loading from the roof, but the span between columns for the ridge beam will be 21'-0 making the ridge beam be 10 x 16 to support the load. Are my calulations right for the ridge beam right?

Thanks in advance
Brian

 

[BrianHa]

Ooops forgot to say we what material we are using, southern pine #2.

 

[JStephen]

I would suggest contacting a local engineer to look at it in detail.

 

[JAE]

To minimize the lateral thrust on the exterior wall you are correct - use a ridge beam. We typically use LVL lumber instead of plain graded lumber.

 

[ToadJones]

load bearing wall down the center?

post a sketch if you can.

 

[FSS]

You definitely have some framing issues to get straight in your head so you can analyze correctly. Structural ridge will help by eliminating the thrust problem, and yes the ridge beam will be big. Why not go with trusses? They might be able to accomplish what you need and you eliminate a lot of your problems.

 

[msquared48]

What you are describing seems to be a collar tie situation, but only if the ceiling joists are continuous and connected to rafters at each end. Depending on the height of the collar tie with respect to the end of the rafters, you could se bending and a small amount of lateral spreading. However, if this is the case, the construction method is done all the time.

And, as previously mentioned, a truss package might be able to be used which would be cheaper than stickframing the roof/ceiling structure.

Best to engaqe a structural engineer as previously mentioned here. There a lot of things to consider here.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask