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Discussion Forum

Installing a joist to an existing floor

| Posted in Construction Techniques on May 17, 2002 08:07am

My 2 story 20 year old house has a major sagging area where a 10′ long load bearing wall on the first floor has been sitting on nothing but the subfloor. I have 2×10′ floor joists spanning 15′, BTW. I have talked to a couple of engineers and they suggest installing a microlam(2×9 1/2) to support the load bearing wall. This is not a case of sistering a joist. One wall is an exterior block wall, the other is an interior wall. So, the question is- after slowing jacking up the floor, how do you get the microlam in place?

Thanks in advance.

Reply

Replies

  1. User avater
    BossHog | May 17, 2002 09:46pm | #1

    Don't know how we could ever tell you that without seeing the house.

    It may be a matter of trail and error - Try one thing, then try another way if it doesn't work. You'll probably have to rip the LVL down to match the depth of the 2X8s.

    Might be easier to get an 8" steel beam in there so you have some extra depth to play with.

    1. Piffin | May 18, 2002 12:04am | #6

      I'm with boss on this- the steel will be easier and less expensive for this one.

      But you goofed boss - he says his joists are 2x10 - not 2x8

      Excellence is its own reward!

  2. JohnSprung | May 17, 2002 11:05pm | #2

    First and foremost, note that I have only done this once myself.  Others with more experience may read this and offer corrections.  If they do, believe them, not me.  If anything goes wrong, my liability is limited to what you paid for the following advice:

    If I'm interpreting this correctly, you have a load bearing wall parallel to the joists of the floor under it, and it rests only on sub floor between two joists?  Over a basement or a crawl space?   Assuming a crawl space, go exploring under there and take a look under the wall. Re-route any plumbing and electrical stuff, etc, that's in the way of where the new girder goes.  I've been working around one piece of electrical conduit that's been a royal pain in the a--.  It would have been much easier to re-route it first. 

    Before any jacking, get the new girder slid into the crawl space, and get it into place.  You can hold it there gently with a jack, but no real lifting yet. Install blocks between it and the adjacent joists to keep it from kicking out and rolling over, but bear in mind that they'll have to accommodate the change in position as you jack.  Figure out where the piers and posts to support it will go, and put your jacks there.  Use steel plates maybe 4" x 6" x 1/2" between the top of the jack and the wood to distribute the load and protect the wood.   Build up cribbing in between where the piers and posts will go, lift everything to just a tad bit above where you want it to be, and transfer the load to the cribbing.  Build up the cribbing as you lift, if a jack fails you want to keep the distance things fall to a minimum.  Put in your piers and posts, then jack to get the cribbing out and the load onto them.  Double check those blocks, and re-set them if they got stressed by the lift. 

    You should expect some plaster or drywall damage on the wall.  If it's a plaster wall, pull the baseboards and rake out the bottom couple inches or so of plaster before you do any jacking.  Studs aren't always all perfectly tight to the sole plate, so it helps to allow for some movement there.  If it has existing cracks that will have to be fixed, rake them out before you lift.  This will minimize the amount of stress that gets transferred to the plaster.

    There are some pictures of my jacking job in the photo gallery, and I'll be adding more soon.

    Bear in mind that this can be real dangerous stuff to do.  Do what you do carefully, and don't do what you have doubts about.  You might also want to run these procedures by the same engineers who sized your beam for you.

    -- J.S.

    1. ivyfalls | May 17, 2002 11:58pm | #4

      John,

      Thanks. I have a full basement underneath this area. I would like to refinish the basement so I am trying to avoid posts.

  3. r_ignacki | May 17, 2002 11:44pm | #3

    to answer youir question , after any shoring/jacking, you mentioned, (who knows what you got out there)  .  One side block wall , o.k.,make pocket in wall, maybe engineer advised you to fill cells solid, maybe not , cut 3-5/8 slot in plate(s) in other wall, nail ml's togeter, nail bearing plate on bottom of beam to go in masonry wall, wrap w/metal flashing, or maybe even ice and water shield, fire cut optionable, or ,grout bearing plate to elevation, get hlp to put in beam, push up to subfloor, slam post under beam in wall, pack n.s. grout in masonry wall under plate, strap across cut plate(s) other wall, whud engineer tell you to do under that int wall? maybe footing, thicken slab, nothing. note: may have to rip ml's smaller 9 1/2? you say, check first.

      

    1. ivyfalls | May 18, 2002 12:10am | #7

      Panama Red,

      I was thinking about cutting a 2"x10" horizontal slot in the band between the existing joists and stick the lm through it about 6" so I could lift the other end of the lm and place it on the interior load bearing wall. Plug the slot in the band. That would place the lm on its side. I was planning on trimming the lm by 1/2"to1"(knocking it down to 81/2-9") on each end for about a foot. That should allow me to rotate the beam vertical and then jack it and shim.

      Concerns about cutting a slot into the band?

      I also like your idea about cutting the block. I was planning to strengthening the interior wall with additional 2x4's.

      1. r_ignacki | May 18, 2002 12:33am | #8

        mis read your post, thought wall was on second floor , etc  masonry wall is foundation, o.k. no need for that pocket stuff,  I don't think you need to do that slot thing either, 8" block? 8"minus 1-1/2 = 6 1/2 thats enough, what's this other wall again, I need reading glasses.  

        1. ivyfalls | May 18, 2002 01:17am | #11

          Panama Red-

          Existing joists are 2x10's. ml's are the same(actually 9 1/2" for joists and ml). Yea, the floor joists support the first floor and I have a full basement with one wall being concrete block and the opposite wall being an interior load bearing wall.

          1. r_ignacki | May 18, 2002 01:44am | #12

            o.k.  I'm assuming that there's room on the other side of this int wall.  Also, ml's are same depth as you say, nails ml's together, there won't be any room to do that when they are up in the joist space, cut plates out of wall as I said before, cut small bevel off bottom of beam(foundation side) approx 1" long, this is to prevent bottom edge of beam hanging up on mudsill, lift beam up into joist space, hold there with blocks well nailed across bottom of joists on either side. Nail short 2x4 flat on edge of beam wall side. Hit this puppy wsledgehammer until it in allthe way in. POST under beam, straps on plate(s) etc etc.  

          2. ivyfalls | May 18, 2002 02:14am | #13

            I like that plan. I guess I was unsure about cutting the plate on the interior side.

            To recap-

            1) Nail 2 lm's together.

            2) Cut slot in interior wall top plate so double lm can pass up though it.

            3) Trim 1/2' on bottom edge of exterior wall end of lm's, about 6" or so.

            4) Push exterior end of lm's into place

            5) Shove/jack/hammer/whatever interior end of lm into place

            6) Secure with post(in load bearing wall)

            One final question, I promise!  What type of post(s)?

            Thanks

          3. r_ignacki | May 18, 2002 02:57am | #14

            don't cut off that much, on the end, just one quarter inch to nothing in one inch , just so the beam is not digging in the sill as you are driving it in . Post size: since it's my job to construct/ install, not design, let some one else size it for you maybe it will be a 4x4, three 2x4's, or a pipe column.  

      2. JohnSprung | May 18, 2002 12:40am | #9

        Notching the end is a bad idea, it substantially weakens the beam.  You'd do better to make your slot vertical, and just a bit higher than needed so you can move the beam.  Then shim up under the end of the beam.  Come-alongs and C-clamps come in real handy for this kind of thing.

        -- J.S.

        1. ivyfalls | May 18, 2002 01:16am | #10

          John,

          I'm probably not explaining myself very well. My thinking for trimming the ml and then shimming it is two-fold

          1) by reducing the ml from 9 1/2 to 9", it will allow me to rotate the ml once it is in a horizontal position on top of the sills. Once in place I can shim the 1/2" in.

          2) with a sag of over an inch, I believe it will be very difficult to force a 9 1/2 ml into place.

          1. JohnSprung | May 21, 2002 10:17pm | #15

            With a sag of over an inch, what you could do is get one end into place as Red suggests with a sledge hammer (come-alongs would be another way, or maybe even both).  That will leave the beam angled down slightly, and at that point you'll have to do the jacking that actually lifts out your sag.  Be sure to have a nice big steel plate between the beam and the jack so you don't gouge the bottom of it.  When the other end is jacked high enough, you can install the post that supports it. 

            Ask the same engineers who sized your beam about the posts, and what goes under the posts.  The load has to be supported all the way to the ground.  The engineers will also tell you that the little chamfer that Red describes is no problem, but notching the end of the beam is.

            -- J.S.

  4. Piffin | May 18, 2002 12:02am | #5

    You refer to a single micro lam.

    Check again to be sure the engineer had all the pertinent information. I have a hard time believing that a single one that size will turn the trick for - especially after the loaded wall and stuff above havew now 'learned' the current position.

    Excellence is its own reward!

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