Built-up Beam

[day_planner]

I want to make an addition to my home over an existing garage.  The garage consists of 2"x6" exterior walls @ 2' O.C. with 15' clear span between the walls.  The addition will have the pre-enginnered joists run from exterior wall to exterior wall but need a beam, which will run parallell with the joists, to carry the area where the wall and roof above are supported.  The roof rafters will have a 12/6 rise with 16" eaves.  I've looked at span tables for built-up beams but can't find one for this particular application.  The built-up beam span table shows a 4- 2"x10" beam spanning 14'-1" with a supported joist length of 8'.  The beam will not be supporting joists just the wall and roof above.  Will this beam be acceptable or do I need to upgrade to 5 - 2"x10" or 2" x 12"?

[John Raabe]

Checking a beam like this involves doing a load trace by carrying down the accumulated loads from the roof to the foundaiton. There are local issues such as snow (and maybe wind) loads, and the total area of these dead and live loads that will land on the beam. There may also be point loads to consider.

If you will be getting a permit then it may require an engineer checking the structure anyway. In that case you may not want to do more than rough size it now. Work up your floor plan layout and exterior design in sketch form and then go to the engineer. By then there may be other things to check such as footing sizes, egress windows, fire code issues, etc.

[day_planner]

Thank you for the reply.  I live in an area not under the jurisdiction of a local municpality and will not require a permit but want to ensure everyhting is done correctly so as not to cause structural problems when completed.  I'll do some research on snow loads & shear to spec.a  LVL beam to see what the appropriate member should be.  I'd rather over design the supporting member rather than discover any problems from not doing enough research.  Thanks

[twobritts]

Take drawings of what you have, and what you want to your lumber supplier.  Any one who sells I-joists or floor trusses will have programs to design a floor system.  They want your floor to work for you.  I used to do this estimating for a lumber yard but don't have the programs at home or I would try to help more.