How To Add Another Support Beam Under Floor Joists - Carpentry - DIY Chatroom Home Improvement Forum

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Old 11-11-2008, 05:03 PM   #1
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How to add another support beam under floor joists

My kitchen/family room ~12.5 feet wide and 30 feet long, built over a dirt-floor crawlspace that's about 4 feet high. The 2x10 floor joists span the 12.5 foot dimension, spaced 16" oc. There is no bracing/blocking between the joists. The floors have been kinda springy since the house was built 14 years ago, but is more noticeable now that we've got full-sized teenagers charging through it!

I'm tired of the kitchen floor moving, and want to add an additional support beam in the crawlspace, mid span under the floor joists. From things I've read elsewhere, this seems like the quickest, easiest, and most effective fix for my situation.

So, I'm looking at a pair of 2x10s running down the 30' direction, supported by 4x4 wood support posts at 8-10 foot interval. What I'm looking for is some details of how to actually do this. How do I join the paired 2x10s (adhesive and nails from what I've read, but how many and what size nails, will I need to clamp the boards until the adhesive cures?). How to span the 30' length (offset where board ends come together, or line them up and make sure they're over the support post? Should I use those hammer-on metal joining plates? Something else?)

What sort of "footing" do the support posts need? (the crawlspace is earth, seems compact at the surface) Do I need any hardware to connect the post to the beam and the beam to the joists, or can I just toenail? something else? How do I get this new beam/posts tight up against the joists so that this effort will actually work?? Any considerations I've overlooked?

Anything you can offer would be most welcome.


LOStouten is offline   Reply With Quote
Old 11-12-2008, 01:35 PM   #2
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I would just use some patio blocks to set the post on. The supports are only adding stability to the floor so you do not need anything fancy.


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Old 11-13-2008, 03:34 PM   #3
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I agree, you're not using the new beam for load bearing purposes. I'd get the longest length you can get in the space and work with comfortably. Glue and nail (3"), no need to clamp, the nails will hold the pieces together 'til the glue dries. I would offset the joints. Brackets may be the easiest way to fasten to the joists. A 4"x4" post every 8' or so (on a solid block) should be sufficient.
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Old 11-13-2008, 10:55 PM   #4
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when you put your beam together nail 3 nails every 12", your spand is only 12.5' the 2x10s should have been plenty.they make a concrete base made for 4x4 they sale them at lowes and home depot.You can put your beam on top of your 4x4s or you can through bolt it with 1/2 carriage bolts if you bolt it you can jack the beam up tight nail it to hold until you can get the bolts in dont try to jack it up much jsut try to get your beam snug,if you jack it up to much you run the risk of your beam flipping out so be careful regards Rob
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