Expert: Bruce E. Johnson - 9/9/2008

Question
QUESTION: I cannot find the specs for the size of door headers I need on a garage.  The doors are on an exterior load bearing wall with no second story.  I have doors that have a 6', 10', and 16' openings.  What are the required header sizes and how many pair of jack studs do I need for each?  Thank you.

ANSWER: Hi Bill, I am not an engineer, however, the rule of thumb for a nominal 4" thick wood beam (or doubled 2X) of southern yellow pine or Douglas fir is one inch of depth per foot of beam.  So in your case the following would be suggested, 4x6 for the six foot opening, 4x10 for the ten foot opening and 4x16 for the sixteen foot opening.  Now 4x16's are getting difficult to come by and the LVL or laminated wood beams are good substitutes and can span longer distances with shallower depths. a double 1 3/4" x 12" LVL can potentially be used in the longer opening.  Contact your local truss manufacturer and see what they have available and what they suggest.  As far as jacks go.  Up to six foot one jack per side, up to ten foot two jacks per side, the sixteen footer should have three jacks per side.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

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QUESTION: Thank you for your help.  My concern is mostly with the 16' span.  And I realize I did not give enough information.  The building is 24' deep, so the roof to be supported would be 12' (half the roof) x 16'.  Maximum load is 10 psf dead load, 10 psf snow load and 20 psf live load (minor attic storage).  So it seems I need 12' x 16' x 40 psf or 7680 lbs of uniformly distributed load over the 16' beam.  How do I find the tables to figure the size lumber needed for this header?  How many 2x12's would I need?  What is the maximum uniformly distributed load for a double 1-3/4" x 11-7/8" x 16' LVL?  Thanks again for your continued help.

Answer
Hi again Bill, each lvl manufacturer has slightly different numbers for their beams..try this link..it is pretty extensive but it is also in metrics so you will need to convert.  Calling a truss company who sells the lvl beams can give you the info you need also..www.nelsonpine.co.nz/Downloads/LVL%20Aus%20E10%20Intr..