Attic space to living space floor upgrade
I know this has been discussed before, but I was wondering about an alternative solution to the undersized floor joist issue. In my case they are 2×6 and 16″ on center spanning 12 ft. Not good enough to convert my attic into a living area with 30lbs live load. I have seen the solutions about sistering the joists and reinforcing with plywood. But I have not seen anyone ever mention slipping another joist in making the joist 8 inch on center. Seems to me like this would be equal to the sistering solution with greater load distribution. This is coming from someone who knows very little about construction engineering. Maybe deflection is too much doing it this way. I’m hoping someone on this great website will have some tips for me. Thank you in advance.
Replies
Look at the 12 inch spacing tables. Remember they depend on species and grade.
If you want to know 8 inch spacing load capabilities, it would likely take a custom calculation. (an engineer could help with this.)
Your building inspector likely will have an opinion, or will specify if you need an engineer to sign off.
By my calcs. doubling at 16" oc would work. There is no advantage to going 8" oc if your sheathing is adequate. As far as span goes double at 16 is the same as single at 8. I've never framed anything 8" oc but it seems like it would be a bitch. Actually double could make a stiffer floor because the two members are nailed together and work in tandem.
Good to hear it's the same load capacity. I thought is would be harder to sister the joists with all the gluing and nailing required. What about fasteners? I'm thinking framing screws with some construction adhesive.
Theoretically you wouldn’t need to attach them at all. Use adhesive and fasteners to eliminate squeaks. Gun nails should be fine if you have good contact for the adhesive
Even if the load capacity is equal by going 8" OC vs sistering, I would think sistering is preferred for a few practical reasons:
- You don't need to worry about adding more hangers
-You can, in theory, patch in the sistered joists if necessary rather than placing full length boards
-If you have to bore any holes, you have fewer holes to make and go through.
-(MOST IMPORTANT) you can actually fit a nail gun/drill/driver in between the joists to fasten anything on the joists or bore holes!
Going 8" OC would be a huge pain, IMO, and I'd avoid it if at all possible.
Didn't think about the spacing for a gun/driver. Excellent point.
Moving another beam to strengthen the slab can be a good solution
What slab?