Expert: Stephen Major (Owner--Major Design Group) - 5/18/2007

Question
I am drawing plans for my new home in Richmond, Virginia.  It's a 1 1/2 story design with cathedral ceiling over the living area.  
I'm planning for roof trusses with a 10:12 pitch, about 38' deep (wide).  Main floor ceiling heights are 9'.  I want to have windows across the back of the living area which will be an exterior load bearing wall.  I also want transoms above these windows mulled together with the lower windows. I have 2 questions:  

1) I need to know how to calculate the height of the header over these windows -- I'm thinking about a configuration that will require 3 separate rough openings with the following widths:  4'1", 6'1", 4'1"  Will a 10" header suffice?  Would any of these require doubling up
king studs or trimmers?  I'm concerned about the amount of space between windows.

2) With a 9' ceiling how high can my windows be set?  I'm thinking 95" allowing for a 10" header & 2 2x4 top plates - is that correct?  

Answer
Laurie,

Your roof load is pretty high in this case.  Assuming a 40#/sf live plus dead load your header will need to support 760 pounds per foot.  Plus if your trusses are 24" on center, then you may end up with concentrated loading on the shorter headers.

In cases like this I would opt to use laminated veneer lumber (LVLs) instead of solid lumber headers.  Use 1-3/4" x 9-1/2" material, doubled and nailed together per mfr. instructions.   I would not double the king studs in any of these openings, and I would not double the trimmers in the 4'-1" openings.  For the 6'-1" opening, if mullion width is a concern, then you can use one 2x4 trimmer laminated (glued/nailed) to a clear 1x4 to get 2-1/4" of header bearing on each end, which should be adequate here.

I assume that you will be getting these building plans reviewed and stamped by a licensed architect or engineer prior to commencing construction.  This professional should double-check the structural assemblies and loads as part of this process.

Best wishes and please let me know if you have additional questions.

--Steve Major