Expert: Bruce E. Johnson - 6/24/2011

Question
Hello Bruce,
I received your reply. Thank you. My garage will be 30ft. Deep so when pull suburban in I will have appropriate parking and still have room for my tools and stuff. My fist choice after building the first floor with 2x6x8 is to run a 30 ft. I beam from front to back which would be supported by a lolly column at each end. Then because the I beam is in the center of the 24' I was going to use 2x10x12's for the floor joists. Then I would run the 2x10's at 16" oc  from the outer wall to the web of the I beam. The top and bottom flange is a little wider to accommodate the lumber. That would give me a 8' ceiling ht in the garages lower area and not have to build a soffit around beam. As far as the gambrel roof I was trying to get a 7'-6" ceiling ht. On the up stairs.
On the second floor I was going to run floor wise 3/4 t&g glued and screwed with 2" screws, run a 30' lvl for ridge and support that with 2x6's tripled up. Then build gambrel roof from there. The walls I was talking about for the (purlin) walls were the walls that kinda square off the room instead of a short knee walls. They come in around 4' from the outside wall, that's ok, rite? I have a 18' ht restriction for our town. The truss company said the trusses were rated for a 25# snows load. I need 30# snow load on the top cord, and they said 2'oc was fine with the 2x10 for the bottom cord. That's why I was asking if I just build it myself it would be stronger floor ( bounce wise)???
I am trying to get the most room out of this and still give me the floor strength.  

Thank you for your time and patience
George Youpel

Answer
Hi again George, like I said before, to get an I-beam capable of carrying its own load plus a non bouncing floor load you will have to get heavy.  I-beams or "W-beams" are rated by weight per lineal foot. A beam the size to meet your flange height requirements would have to be a W-10 or possibly a W-12, the distance between flanges vary between 10-12" depending on the designation..You will have to have an engineer determine what beam weight will work for that long of span.  Something that weighs around a hundred pounds or more per lineal foot may work..check with an engineer for exact dimensioning..otherwise your other design criteria seem okay..I don't see why the truss company can't build you a roof with the required snow load you are asking for or the proper span for the floor joists involved..you need some engineering help on this because your design criteria is out of whack from what I can see..sometimes what we want and what the reality is are two different things..sincerely bruce johnson