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Beam structure to support two joists

Posted by austinspace (My Page) on
Tue, Sep 7, 10 at 20:39

Hello, this is my first time posting. I have a load bearing wall that I want to remove. The critical load it is carring is two sets of neighboring joists, a span of 32". Having concluding that I can't successfully replace or reinforce/splice these joists so their load can be carried by other walls, what I would like to do is replace this wall with a beam below the joists, about 4' long. The ends of that beam would be attached with hangers to 8' long members, running perpendicular to the beam. These 8' members are supported by posts/studs at each end (a total of four posts). Where the posts are located can easily be integrated into existing walls, so that I have a clear area where the bearing wall used to be.

Here's a sketch of the current situation, showing the framing: joists, brick wall and the supporting wall. The far ends of the joists are properly supported (not shown). All joists are full 2" thick by 7-1/2" tall. The light wood colored joists are the ones the need support. The black cylinder represents a toilet drain above -- presumably one of these joists was cut to allow for this drain, way back when.

And here's a sketch of what I'm proposing to do:

Questions that I have are:

1. what should be the dimension of the 4' long beam

2. what should be the dimension of the two 8' long carrying beams?

3. is there a better way to do this?

- John


Follow-Up Postings:

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RE: Beam structure to support two joists

... my thought was to use double 2x6's as the beam, attached by beam hangers to double 2x8's at each end. Looking for validation on size of lumber here, and the design overall. Thank you.


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RE: Beam structure to support two joists

Without a floor plan it's impossible to say if the post placement makes sense but the loads from the posts should be carried to the foundation through appropriate structural elements (beams, joists, etc.).

The beam connections to the free standing posts are unstable; perhaps parts of the posts could go to the roof.

Without knowing the spans (unsupported lengths) of the cut roof rafters and the roof loading it is not possible to size the beams other than by guessing.


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RE: Beam structure to support two joists

John,

In the first picture you have the right idea of a temporary supporting structure while you do the work. If the existing joists are 2x8's then you should double or even triple the ones that will stay on either side of the proposed opening (known as "trimmer joists"). Of course the span of the existing joists will dictate whether you need to double or triple the trimmer joists. The trimmer joists will have to be supported on both ends to carry the weight of the load. The ends of the trimmer joists nearest the brick wall can have a 2x ledger board attached to the brick to provide support but should also have a number of 2x's layed flat against the brick under the ledger from floor to ledger to give additional proper support to the ledger.

The "cross beam" also known as a "header" or "girder" should be a double 2x8 header supported by joist hangers. This should eliminate the need for any supporting posts underneath giving you a true clear area.

Hopefully this helps.....


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RE: Beam structure to support two joists

You could save a lot of effort by installing a flush header between the two solid joists, and then notching 2 posts to the joists as near as possible to the header. As has been said "something" needs to carry the load to a suitable girder and ultimately the ground. IOW it won't do to support this on just flooring or just another joist beneath the flooring. I would investigate a second header at the brick wall, and removal of the old inadequate (cut) joists, and installing new short joists placed to miss the plumbing.
If you are resigned to having posts, there is no real need IMO for four of them, two would suffice if they have bearing on structure.
Casey


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