Joist Sistering 101 (Photos!)

[Bea Tyler]

Hi all,

Finally finished sistering my joists. We’re tiling a room that had 2x10 joists 16” apart spanning 15’. The deflectolator gave a reading of L / 318, which is why the extra strengthening was needed. We decided to sister the joists with 2X10’s 12’ long, where the new joists would not reach either end. Go here to read more about that process:

http://www.johnbridge.com/vbulletin/...threadid=10261

These photos show what I started with, and some of the obstacles I had to deal with.

Bea

[Bea Tyler]

I used a decent thickness metal strap to suspend one end of the joist while I clamped the other end. With one end clamped, I clamped the suspended end and jacked it up to butt against the floor. Sometimes the jack would force the joist away at the top, so I hammered another temporary brace in till I could get screws in.

[Bea Tyler]

Where there were a lot of obstacles I had to use two suspension straps, then roll the new joist into position. After all the joists were in, I put solid blocking in midway along the span. I left the cross bracing where two sisters were both put outside a space. The jack was useful in holding the blocking in place where it was slightly loose, and in cinching it up to the floor where it was slightly tight. Note the temporary back bracing to keep the blocking from moving as it was toe-nailed from the other side.

[Bea Tyler]

The blocking got ten #16 3 ½” nails each. Holes were pre-drilled. Tops of blocks were glued before going in, then all seams were glued front and back. Joists and blocks were screwed into from the floor above. This photo shows the job almost complete, just a little more gluing to go. The floor is MUCH stiffer and now rates somewhere in the vicinity of L / 638.

Thank you very much to all who helped get this far along – Whew, NOW I can put down some backerboards!

Bea

[davem]

Bea,
Very nice work. And thanks for taking the time to document it an post it here. I'm sure that will help a lot of people.

[stullis]

Nice job! I bet the floor feels much better when walking across it compared to before.

Quality always pays off.

[rat4spd]

Magnificent! Must of been nice not to deal will zillions of nails sticking through the subfloor poking you and making it difficult to put the joists in.

[John Bridge]

Nice work.

Dave, maybe you can put this in the liberry someplace. I'd do it, but the liberry is getting messy again. You do such a nice job of keeping things organized.

[Bea Tyler]

Thank you for the compliments - and a potential spot in the Liberry?? I'm honored!

Here's hoping the visible part of the job has as good an outcome!

Bea

[Jammin1]

Is the blocking required? What does it do for the situation?

[MarcusEngley]

Hi Bob,

The blocking keeps the joists from twisting along their length as they age/dry out. It also helps minimize plywood deflection between the joists.

Cross-bracing (as in Bea's first photos) doesn't do much for deflection, but serves the same anti-twist purpose as the blocking. Ties the joist to its neighbors, basically.

Hope that helps!