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-   -   what size beam for jacking up floor joists (http://www.diychatroom.com/f19/what-size-beam-jacking-up-floor-joists-63628/)

ponch37300 02-04-2010 06:45 PM

what size beam for jacking up floor joists
 
1 Attachment(s)
I posted my sagging floor joist issue a couple weeks ago and have decided on jacking up the existing floor joists using a temp beam supported by 4 columns at the middle of the floor joists. Then when all is level I will sister 2x10s to the existing 2x8s. My question is what size beam should I use for the temp beam? The beam will be 23 feet long and I'm thinking 4 support columns, one at each end and 2 in the middle so it would be right around 7 ft in between each column. This temp beam only needs to support the middle of the floor joist and what's on them. There is no supporting walls on top of it so it doesn't need to hold the whole house up. I'm thinking that double 2x6 or 2x8 should do for this? Here is a drawing that helps to explain the situation.

Attachment 17417

tpolk 02-04-2010 07:00 PM

how you getting the 2x10 over the beam

Big Bob 02-04-2010 07:18 PM

Can you post a link to your previous postings on your floor joist issues?

It might help us or at least me understand why you are taking this approach. Is the sag uniform at the middle for 23 ft? What does the string tell you?

what is your plan for sistering the 2x10 to the 2x8 at the temp beam area. notch your temp beam or block up directly under the 2x8 from the temp beam. OR Notch the 2x10 around your temp beam:eek:?

Think about renting some post shores (screw jacks).

Let us know.

ponch37300 02-04-2010 08:29 PM

Here is the link to my other thread http://www.diychatroom.com/f19/need-...support-62366/. The floor is sagging becuase it has 2x8s spaced at 16" that span about 15'.

I bought 4 "screw" jacks since I'm not sure how long this project is going to take so renting might get a little expensive.

I plan on using a spacer in between the beam and existing 2x8s so I can slid the 2x10s in. I'll have to do a test to see if I can slide them in with the temp beam in place.

jlhaslip 02-04-2010 08:36 PM

Don't forget that you need to be careful with the bottom of the jacking system.
It will be placing a whole bunch of weight onto the floor system it is raised on.
Check to see if you need to support the floor underneath with other jacks/posts before they get loaded up.

Best to carry the temporary loads all the way to the basement/ground.

ponch37300 02-04-2010 09:59 PM

Quote:

Originally Posted by jlhaslip (Post 394933)
Don't forget that you need to be careful with the bottom of the jacking system.
It will be placing a whole bunch of weight onto the floor system it is raised on.
Check to see if you need to support the floor underneath with other jacks/posts before they get loaded up.

Best to carry the temporary loads all the way to the basement/ground.


This will be in the basement to jack up the first floor so as long as the cement which is in pretty good shape can hold the weight I'll be alright.

jlhaslip 02-04-2010 10:09 PM

Quote:

Originally Posted by ponch37300 (Post 394991)
This will be in the basement to jack up the first floor so as long as the cement which is in pretty good shape can hold the weight I'll be alright.

I would still place some 2 by's and plywood under the system to spread the weight around.
Do you know how thick the concrete is or are there footings near there? Better to jack at the footings.

ponch37300 02-04-2010 10:21 PM

I was thinking about laying a 2x12 about 2 feet long down flat to help spread the weight a little. I doubt there is any footers in the middle of the slab. The post on each end of the beam should be close to footers since they will be by the foundation wall, but the two posts in the middle probably will just be on the slab.

Thanks

scott j 02-05-2010 10:07 AM

Cracks
 
I have a brick fireplace being held up from the basement that is on 2x8 joists with screw jacks. I still see concrete cracks even though the previous owner used 1 2x8 wood under the jacks.

ponch37300 02-05-2010 10:14 AM

I think I'm going to cut 2 foot long peices of 2x12s and a peice of 3/4 plywood 23"x24" and make a pad that will have 2 2x12s under a peice of 3/4" ply and hope for no cracks. This should spread the weight out over a 2x2' area. This is just going to be a temp beam and posts, just using it to raise the joists and level things out before I add the sister joist.

Big Bob 02-05-2010 03:05 PM

tpolk and I cross posts... but I think the same thing has got us scratching our heads.

your in a basement.. assume these are solid walls and you don't have a row of window to stick the boards out...

I don't think you will have enough angel to get the full length sister board in place once the beam is in place. Maybe with a good fire cut end...?

1. I guess you could tack the sisters in place then set your temp beam.

2. If it were my project I would forget the temp beam... run a lot of string and line levels... keep them tight... once every hour... and work the sisters in one at a time. I think that beam is going to be in your way alot.

You might want to try a dry run and see how your plan is going to work.:thumbsup:

Daniel Holzman 02-05-2010 03:25 PM

I'm with Bob, I cannot visualize the advantage of your approach versus jacking up each joist individually, of course very slowly, until it is level, then sistering the new joist to it. One jack, one pad, no interference. The only advantage I see about the beam is you get to jack all the joists simultaneously, but I don't see how this will save you any time, considering the difficulty of setting up the beam and jacks, advancing each jack individually, checking each joist for level, etc.

By the way, the joists you jack up to level are going to be under considerable stress because you are changing their shape. You are going to need a lot of nails or structural screws to adequately connect the new joist to the old joist. Also, after you release the jack, the paired joist is going to move downward due to the release of energy in the old joist, so if you are looking for a level floor, you are going to need to overcompensate during the initial jacking. Exactly how much will depend on the species of wood, dimensions, amount of deformation of the joist, and the location of loads above the joist.

ponch37300 02-05-2010 05:44 PM

I was thinking that putting a temp beam in would allow me to raise the whole floor at once, avoiding raising one joist and not the one next to it. Just thought that it would be a lot of stress on the sub floor if I raised one joist and not the one next to it. I was planning on giving this a test run to see if I can slide the new joists in over the beam. It would probably be faster to do it without a beam but I was worried about the stress on the other joists.

I'm not necessarily trying to get a perfectly level floor, more trying to stiffen up the floor because it has a "bounce" to it.

Thanks again for all the advice and ideas!

HooKooDooKu 02-05-2010 11:58 PM

My thoughts are along the same lines as Bob.

You could jack the floor up on joist at a time if you first block all the joists together. That way as you jack one joist up, the blocking will pull the neigboring joists up with it. Presumably it won't put much strain on the sub-flooor. Conceptually as you jack one joist up 1", the next joist will raise 3/4", the next on 1/2", etc. You could even use a short beam to jack the neiboring joists up in this type of pattern. At one end of the beam, jack it up to level the floor. The other end just barely jack the joist up. As you get one joist sistered, move the system down to the next joist. To avoid raising and lowering the floor, use two beams. Rather than take down the 1st beam, use the 2nd beam to jack the next set of joists up.

ponch37300 02-06-2010 08:14 AM

Quote:

Originally Posted by HooKooDooKu (Post 395516)
My thoughts are along the same lines as Bob.

You could jack the floor up on joist at a time if you first block all the joists together. That way as you jack one joist up, the blocking will pull the neigboring joists up with it. Presumably it won't put much strain on the sub-flooor. Conceptually as you jack one joist up 1", the next joist will raise 3/4", the next on 1/2", etc. You could even use a short beam to jack the neiboring joists up in this type of pattern. At one end of the beam, jack it up to level the floor. The other end just barely jack the joist up. As you get one joist sistered, move the system down to the next joist. To avoid raising and lowering the floor, use two beams. Rather than take down the 1st beam, use the 2nd beam to jack the next set of joists up.

This sounds like a good method. I have 4 jack posts right now so I can get one more and then will have enough to jack one truss up and also have 2 beams so I can just keep going. This idea eases my questions about raising one beam at a time. Thank you all for your suggestions.


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