garage ceiling joists

josh123

hi- this is my first post to the site.
i've got a 31' X 21' garage with 2" x 6" ceiling joists spaced 48" o.c. running the 21' direction. i want to hang drywall on the ceiling. if i install two 2" x 8" joists in between the existing joists, they will be 16" o.c. if i am hanging 1/2" drywall is it alright to leave the existing 2" x 6" joists or should i replace them with 2" x 8" joists? i've read that you can't go smaller than a 2 x 8 with a span of 21'. i just need to know what the best way is to frame the ceiling for the intended weight. i appreciate the help.

Big Dave

Are the joist running the full width without a beam?

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manhattan42

According to the International Residential Code 2003, you will need all 2x8s 16" on center for an unsupported span of 21' when using SPF lumber. And doing it this way will not permit you any storage to speak of in the attic on the joists.

If you want minimal storage, you will have to go to all 2x10s and frame them 12" on center when using SPF.

There are alternate ways you can achieve what you want using 2x6s, but it involves using stronger more expensive grades of lumber like Doug Fir or Hem Fir, and you may still have to go to 12" on center spacing depending on the species and grade you select.

josh123

thanks for the help.
yes, i am running the 21' length without a beam (as long as that is acceptable), and there will not be any weight on the joists (no storage above) except for the weight of the 1/2" drywall.

Reyes23

Use hat channel.it's a metal stud it goes perpendicular to the ceilng joist and screw it on every 12"

Gary in WA

The existing ceiling joists are over-spanned for drywall. They are only rafter ties, hence every 4'o.c., to keep the walls from spreading.

You need 2x10's on all, including sistering the 2x6's, as Manhattan said. http://www.mcvicker.com/resguide/page013d.htm

Or a structural beam to reduce the span. Be safe, G

Reyes23

Or why not drywall to the roof rafters and have a volted ceiling. I did this to my garage.