I have a detached garage that I'd like to finish the attic space to make into a office like workspace.
The garage ceiling joists are 2x8x14' (unnotched) with a 13'6" span on 16". The joist appear to be SPF but are unmarked. I suspect #2 or #3, but if #3 then I should probably increase the strength. Any good way to identify the grade?
If #3 then AWG.org reports that the L/180, w/25 psf max span is 13'6". With #2 >40psf for the span is allowed.
The attic floor would be 5/8 OSB and the garage ceiling either 1/2 drywall or OSB sheeting.
I'll post some photos shortly.
Best Answer
Code requires a Live Load of 40 lbs. per square foot plus a Dead Load (flooring, joists, insulation, etc.) of 15 psf (probably) for a total load of 55 psf.
#3 spruce/ fir (fb = 1200 psi & fv = 95 psi) spanning 14’ will support about 40 psf at 16” oc. #2 (fb = 1750 psi & fv = 120 psi) will support about 60 psf. The main difference between #2 and #3 are knotholes. If you have loose or missing knotholes, then it’s probably #3. If the knotholes are less than 2” in diameter and “tight”, then it’s probably #2 and better.
Code requires 1-hr. fire protection between a garage and “habitable space”. Therefore, you’ll want 1/2” Type C or 5/8” Type X gypsum board on the bottom of the floor joists, wall by stairs, etc. for protection.
The door leading to the upstairs needs to be rated: 1) solid core, and 2) frame needs to be solid material (no applied stop), 3) weatherstripping around on 3 sides... but consider threshold too due to fumes.
If you use L/180 the gypsum board will crack under deflection. I’d use L/360...then, no cracks.