Expert: Dan Griffin - 1/27/2010

Question
QUESTION: Hi, I am re-supporting my garage that currently has a 2x4 beam as the main structural support. We know that we need a new beam, but we are not sure if we need double or triple 2x6. We also would like to only have one support beam in the middle.

ANSWER: Nick, we need a lot more data to answer the question.  Are we holding up the roof of the garage with something like an attic floor?  We really need to know what you are holding up (what kind of loads are pushing down on what kind of joists - example: attic floor with heavy storage carrying about 60 #/SF on 2x8 joists on 16" centers and a gable roof with mission tile) and how big the whole thing is (example:20' x 24' with a beam down the center of the 20' dimension with one post at eh mid point).  A triple 2x6 is not very strong over much distance...

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

QUESTION: Hi, yes i am holding up a roof and attic storage with about 1500lbs in it. We have 2x4 joists that are about 24" apart. The dimensions of the garage is about 18'x18'. We currently have a 2x4 beam down the middle and one post. we would like to still only have one post but a stronger beam since the one we have is starting to crack under the weight.  

Answer
324 SF
1500#
about 5#/SF live load if uniformly distributed
I suppose the load is concentrated in the middle of the attic.

As you can see here, the joists are ok for 10 pound live loading:
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Southern+Pi

Double check with a good lumber yard, but triple 2x6 or double 2x8 should work.