Building new house, few structural questions

[JeffNH]

Hello,

I found this site a while back when researching flitch beams and just registered so that I could ask for some feedback on a few things. I have a BSME but have never worked in the field and have been out of school a long time so my skills are rusty to say the least.

I am building a new house, 42'X 36', two story with a hip roof. Having an 8 on 12 pitch, my common rafters will be about 24' long. So if I don't use trusses, I am going to have to build knee walls. What I was wondering is how is a knee wall supposed transfer loads downward? It looks to me like in most any building, unless very large, it would be very impractical to have a load bearing wall underneath, since it is going to be close to the exterior wall. (7'6" to have a 5' knee wall in my case). I have also noticed in a few carpentry books I have looked at that they show knee walls being unsupported below in the illustrations but don't explain why. My only guess is that the knee wall would act as a beam after it is sheathed if not supported below. Would appreciate any comments on this.

Also, I have wondered why when hip roofs are explained in carpentry books, the hip portion is always assumed to have the same slope as the main roof? I see alot of roofs that have steeper hip portions and IMO, unless the main roof is steep it looks better. I am going to have a split gable on the front over the foyer that extends out slightly from the front and am going to make it 12 on 12 along with the hip portion of the roof. I am doing this so that I will only have one valley and still have a nice looking roofline. I wonder if this will make it difficult to have trusses built if I decide to go that route. I would also like to know if anyone has experiece with trusses this size and with hip roof trusses that could give me a rough idea if trusses would be cost effective vs. rafters. Sorry to be long winded, thanks, Jeff.

 

[bylar]

From what yuo have described I don't see a problem. The rafters can be 2x12 @ 16" o/c and if as you say, only 24', you can get them in that length. You may consider TJI's for rafters the kneewalls carry no load in either case.
As for the Hip being steeper, I live in NC and I seldom see the hipped end steeper than the main roof. remember the hip rafter has to be sized accordingly and probably will be an LVL. I don't know what an IMO is?
If you are not using the attic space then trusses usually are the cheaper route all around and the two different pitches are no problem to the truss company.

 

[boo1]

Agree with Bylar, consider manufactured beams. Most designs I have worked with use trusses with the same pitch on all the roof. Before you sink your heart on 12/12 pitch get a roofing estimate, it might surprise you.

 

[TFL]

IMO = in my opinion