Expert: Bruce E. Johnson - 11/19/2008

Question
QUESTION: I am building a family room which will be built much like deck in some ways.  2x12' floor joists will be used (partially for insulation purposes.  One end of the family room will attach to the side of the existing house outer wall, with bolts much like a deck extension.  Then, I'm running a double 2x12 support beam parallel to the house at approximately 6.5'.  At approximately 13', the family room joist, coming straight out from the house, will cross over and be supported by the outer wall of the detached garage (the landscape leaves the garage at a significantly lower level than the first level of the house, where the family room will extend from).  The family room will then extend beyond the outer wall of the garage and on to the center of the garage (the garage is 20' wide, so the family room will extend 10' over the garage.

The walls and roof of the garage haven't been built yet.  I figured if I ran 2x12's the length of the garage width for the ceiling of the garage, it would accomodate some of the weight of the family room's live load.  I also figured I could run a support beam the 21' length of the garage under the center of the garage ceiling joists.  My challenge ist that the garage will be from an old carport, with footers only along the outer perimeter of the carport.  Therefore, I would like to try and have the center support beam held up only at each end of the garage, with no center posts.  I believe the live load of the family room will be 50psf.  Not having any experience with steel support i-beams, and not believing that sistering several 2x12x21' wood beams would work, can you help me figure out the garage center-support beam requirement?

... the outer wall (non-load-bearing) of the family room will run the length of the support beam at the center line of the garage width, and the other half of the garage will be roofed (with the roof leaned against the side of that family room wall).

ANSWER: Hi Steve, The following beam span chart should help you figure you beams sizes.  It looks like a W14x22 would probably work however I am not an engineer and always recommend that structural engineers be consulted for final structural approval of your design.

http://store.steelframingalliancestore.com/restbeandcot.html

I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

---------- FOLLOW-UP ----------

QUESTION: Thank you very much!  I don't see the end-beam support requirements in this link.  What are they for a W14-22, 21' long?  

Answer
Hi Steve, generally speaking any solid support the width of your beam should suffice.  A 4x6 or 6x6 or a 6" steel column..I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com