Tuesday, December 15, 2009

Rough Wiring and Half-Sistered Joists

Lately I've been trying to get some of the rough wiring done, but this is another one of those jobs where I can't do the main task-at-hand until I finish another seemingly non-related task.

I'm planning on putting ceramic or porcelain tile throughout the house. One of the prerequisites for laying tile is a strong, stiff floor. If the floor flexes, the grout between the tiles can crack. In order to help stiffen the floor, I'm reinforcing all the floor joists by screwing and gluing a 12" wide piece of 1/2" plywood to one side of each joist. (When renovating existing homes, sagging floors are often fixed by installing new joists directly beside existing joists. That's called "sistering the joists".)

Since a lot of the wiring will run through the floor joists, I need to get the joist reinforcement done before I can run any wiring. Once the joist reinforcement is done, I'm able to drill some holes and run my wire through the joists.


  1. I am just curious why you are having to strengthen new joist? I see why this would have to be done in a older home but not a new one? Maybe I am misunderstanding though because it does not seem that a 1/2 piece of plywood would provide much strength. Thanks, and I really enjoy checking in on your blog every once in a while.

  2. Hello there! Thanks for checking in.

    Well, I admit that it might be a bit of overkill to add support to the joists... but it's one of those things that I don't want to regret "not doing" later. It's much easier to do it now; before all the plumbing and electrical is in.

    The engineered joists are very strong, but they do flex a little bit; especially over a 16' span. The plywood does add a significant amount of support, because the stress being applied to it is being applied to the edge, rather than the face.

  3. That makes sense. Thanks for the response.

  4. I just screwed down 1/2" hardibacker to the top of my 3/4" subfloor and that made the difference for stiffness.