Need help with sistering floor joists.
I need advice on strengthening a floor. The house in question is sold, but the home inspector noticed that the drywall in the dining room ceilng was cracked. He went upstairs and began jumping on the floor above the dining room. Considerable bounce. Apparently, the room above was previously storage space. He assumed that the joists were undersized for the span. (The room is 12 x 14). The buyer now wants the floor strengthened. I went to look for myself before bidding. It seemed to me the floor would be easier to strengthen from above; instead of tearing out the celing from below. (Partly because the plaster was curved in the corners—tray ceiling, ) Also, a new subfloor would need to be glued and screwed to the floor to increase strength. Luckily, I discovered, the room behind the room in question was infinished. I pulled up the plywood and discovered that the room in question’s joists were 2 x 8’s that had been notched on the top to accept the new partition wall. (Why they did it that way I have no idea.) My question is:
Due to the notching, is the joist effectively a 2 x 6 since that’s the measurement on the end?
Does the new sistered on framing member have to go bearing to bearing? (I can get bearing on the interior bearing wall, but unfortunately in the upstairs room, the outside wall is in a few feet in from the roof of the first floor. (If you look out the window in this wall, you can see a few foot of roof above the first floor…I hope that makes sense!). I don’t think I can thread a new 2 X 8 all the way. Would I be better to sister on 2 x 6 bearing to bearing or a 2 x 8 with bearing on one side, but joist hangered between the other joists on the outside end with a nailing schedule of every sixteen inches?
If I can’t get to both bearing points, won’t the floor still stiffen just with the added lumber nailed to the joists. Once the new subfloor is glued and screwed shouldn’t that take out the majority of the bounce?
Sorry to spring such a long email on you. I think I may have WAY underbid this, if I have to tear up the roof to thread new joists into the bays….
Edited 10/20/2005 1:28 am ET by Cooper
Edited 10/20/2005 1:30 am ET by Cooper