Expert: Ted Barnhill (Principal, Design45 LLC) - 7/27/2007

Question
QUESTION: Mr Barnhill, I'm planning on replacing part of a load bearing wall with a pass-through opening (about 5ft long)supported by a beam. The problem is that this load bearing wall is sitting on the 1x4 sub floor between two floor joists rather than directly over one joist. What sort of additional reinforcement would be necessary to support the posts at either end of the new beam? Would it be sufficient to connect the two joists with blocking directly under the posts, or would it be necessary to install another joist or beam directly under the wall?

Thank you,

Alex I. Ontario, Canada

ANSWER: Is the wall really load-bearing?  A load-bearing wall should rest on a beam, foundation or another load-bearing wall, to get the loads down to the foundation.  It sounds from your description that the wall is parallel to the joists below it, and sits midway between two joists.  If the wall is load bearing, then the weight of the (many) joists or rafters above is being transferred by the subfloor over to two single joists - which would likely be inadequate.  I would hesitate to create point loads (the posts) in an overstressed situation without understanding all of the loads involved.  If you aren't confident with basic load calculations, I recommend you get an engineer to look at it.

---------- FOLLOW-UP ----------

QUESTION: It appears to be load bearing; floor joists from the floor above intersect above and are supported by the wall. It is indeed parallel to, and sitting between, two of the joists below it. I was concerned with exactly that, the point loads being applied to the sub floor; which is why I was anticipating having to place a beam or joist directly under the wall, but then I thought that connecting the two joists directly under the posts, so that the blocking is transferring the load to the two joists might accomplish the same thing and would mean that I wouldn't need to move a lot  wiring and plumbing. Would doubling up the two joists and then using two 2x10's to connect the two joists directly under each post fulfill the aim of transferring the point loads to the joists?

Thanks  a lot for this, it appears to be a bit of an unusual situation.

Alex

Answer
Your proposed solution sounds like an improvement over the existing (probably inadequate) structure.  Certainly blocking between the joists, on face-mount joist hangers, can carry the post loads over to the doubled joists.  It would still be an unusual resolution, and the two doubled joists may still be theoretically inadequate, depending on span, loads, etc.  If you are moving plumbing, etc. anyway (in order to sister the joists) I recommend that you size an appropriate beam (maybe 2 or 3 9-1/4" LVLs) to carry the entire load bearing wall.  Then you can be sure that you have fully fixed the existing inadequacies.  Do it right, do it once!