Expert: Dan Griffin - 3/10/2008

Question
I'm building a 24x48 foot garage and need to know what size 2x I need to span 24ft I'm in California.  I have 2x8 on the apporved plans but a contractor told me I need 2x10.
Thanks, Giles

Answer
The dead load of materials is 10# per square foot, and I think the code will require an additional 10# live load minimum.  This assumes drywall and VERY minimal storage.  If you intend any storage, you need a better live load.  You sure won't be pulling any car motors with them.

Here is a pretty good, easy to use span table:
<http://www.awc.org/calculators/span/calc/timbercalcstyle.asp>

In my area, the normal framing lumber is #2 southern yellow pine.
I assume you plan on rafters at 24"o.c., which demands that you place the ceiling joists at 24.

The maximum span on 2x10 is 20'- 9"
By going to 16" centers, the 2x10 will span 25-5, but the rafters will be on 16 centers also.

2x12 on 24" centers will span 24-4

By changing the lumber grade to dense select structural grade lumber, and using 12"o.c., the best span I can get for your 2x8 is 23-9.  YOu would need to check on the availability for that grade of lumber.