jacking a floor,what to use
alwaysoverbudget
| Posted in Construction Techniques on
i have a 1st floor that the ends of the 4 joist have rotted off and created a 1.5″ sag. this is over a bsaement with a 7.5′ ceiling. what is the best way to rig to jack these up. i just can’t come up with something to set a 20 ton pot jack on. larry
hand me the chainsaw, i need to trim the casing just a hair.
Replies
this is sort of a bump, but I'm unsure what your saying in your post. Are you saying 4 individual joists are the problem, or are they 4x dimension lumber?
the ends of 4 of the floor joist [2x10] have rotted off and dropped off the sill plate letting the floor drop ,along with other things!. my problem is i don't know what to sit a jack on with this much pressure.easiest would be to cut off about a 6x6 and stand on end and put the jack on it. but if isn't perfectly straight up and down i'm scared it could kick out. and i really am kinda fond of my teeth! just looking for a way to set this up. larryhand me the chainsaw, i need to trim the casing just a hair.
Are you talking about having to set the jack on the first floor rather than the basement or crawl space floor? If so, you have to start by shoring up the first floor joists and maybe installing some temporary blocking between them. Then, lay a chunk of 4x12 or 6x12 on the floor and set your jack on that, it will distribute the weight.
Maybe I don't understand the question.
it's clear as mud to me! i'm working in the basement and have seven and half foot from the cement floor of the basement to the bottom of the floor joist. so what i need is a platform about 6 foot tall to sit the jack on and start jacking against the joist.
i looked at piffins house jacking post.i could do cribbing like that but it would take a lot of wood to get to 6'. thanks larry hand me the chainsaw, i need to trim the casing just a hair.
You're overthinking this. If you have a flat, level concrete floor to jack from then you're golden. Set the jack on the floor and use a 4x4 on top of it that's cut to fit up against the joist. Just make sure to keep the 4x4 plumb and jack slowly. We're talking about going up 1-1/2", right? That's nothing.
If you have 4 joists in a row to jack, get a chunk of 6x6 or bigger and tack it to the bottoms of those joists, running across them. Then use two jacks and two posts to jack the 6x6.
The setup takes time, the actual jacking does not. Generally you have to sacrifice some 4x and 6x material for a job like this (i.e. buy 8's and cut them down a bit so they are no longer useful in wall framing). I have a collection of short posts I use for jacking.
How lucky do you feel?
Steel lally columns as described with a screw jack at the bottom work great , fasten the top to a cross piece that is fastened to the joists and jack away, use two if the load is heavy.
Cribbing is definitly the best for any kind of serious weight.
That being said....
I have done some crazy things jacking up joists, But after a few close calls I learned to do a couple of things that helped. You can do your jacking off a 6 x 6 column. The biggest trick is to figure out some way to brace your column so that it can't kick out on you. Take a good look at what you are dealing with , can you brace off a nearby wall? How about diagonals from the joists that are solid?
Maybe a full sheet of ply (3/4) that you can fasten 2 x 4 cleats to so that you can build diagonals off of it. A couple of 2x6's fastened to to each side of the column at the base to create outriggers works,(+) shape, but one 2x6 for each face of the column, with ply wood triangular gussets
Don't forget the steel crush plate on top of the jack , it will keep the jack from burying itself into the joists. Go slow, take your time, STOP/LOOK/ LISTEN and always have your avenue of escape planned. ;-)
see if i got he picture right. take a pc of 3/4 ply and lay on the floor, place the jacks on the plywood with the post running up to the joist. then screw some cleats on out at the edge of the plywood with a diaganal running to the top of the jacking post? if thats right that sounds like it would work to "safety" the post. thanks larryhand me the chainsaw, i need to trim the casing just a hair.
Some people like to put the jack on top of the wood and I've seen quite a few that will put a 4x4 vertically on top of the jack. If you go EASY with the jack and don't take up too much at once, they are pretty stable. Keep plenty of studs handy and don't jack it all up in one place at one time. Do a little here and a little there.
Piffen's got(had?) a great thread going on jacking up a building. That gets a bit more complicated but if you want to see how to do cribbing, check it out in the Photo Gallery.
Don K.
EJG Homes Renovations - New Construction - Rentals
Get several lally column type screw jacks. They'll do the job by themselves, or you can use them as safety blocks for a hydraulic. If you use the short hydraulic, put the 4x4 or whatever on top, not on the bottom, and tack nail it to the joist that's being lifted.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
I don't know if they're still available, but a long time ago, I owned a house that had adjustable steel columns someone had installed in the basement to jack up a sagging floor. They were steel tubes, one inside the other with pins & holes about every 6 inches to adjust the height, and a short screw jack built into the top. I don't have a clue what they were called.
Sometimes they are called teleposts. They are reasonably cheap and easy to handle. last time I looked, Sears had them (among others).
Don K.
EJG Homes Renovations - New Construction - Rentals
I would use your 20 ton jack and just take care to make sure that the jack is sitting on a level, firm surface and that the post starts out and stays plumb.
If you really wanted to be safe, I would get someone to weld up a couple of steel plates that have upturned edges to keep the 6x6 on the plate and a piece of tubing welded on the bottom to receive the top of the jack.
Ultimately, I'm confident that as long as you go slowly enough and keep some backup shoring you will be fine.
Jon Blakemore
RappahannockINC.com Fredericksburg, VA
i have a 1st floor that the ends of the 4 joist have rotted off and created a 1.5" sag. this is over a bsaement with a 7.5' ceiling. what is the best way to rig to jack these up. i just can't come up with something to set a 20 ton pot jack on. larry
That's an easy one. We just use 2x4 studs. Cut a little long and wedged inbetween a top and bottom plate to put a lot of lift over a wide area. It seems to work best to screw the top plate in place and screw the top of the stud directly under the floor joist. Parifin on the end of the stud will produce nearly 50% more uplift.
Need twice the uplift? Add a second stud next to the first. We've lifted large areas of houses off the plates with one stud per joist.
Beer was created so carpenters wouldn't rule the world.
I just did this exact thing how ever it was more like thirteen or fourteen. and the studs were rotten as well. You can (here anyway) rent the screwjack shore posts. you get a 6x6 and strap it up to the bottom of the joists where they are sound ( we used pluming strap so all you have to do is unscrew one side and it comes down) and then put one shore post about a foot in on each end there are nailing holes in the top plate so you can secure it to the 6x6with a duplex nail. this stops it from falling over as you jack. I had 2 12 ton jacks that I put on a couple of scrap ends from a microlam I had saved. just enough to distribute the pressure a little. we nailed 2 2x6s together and jacked with that. jack a little, screw the shore up tight, jack a little, screw a little. amazing how fast it went. we did four joist at a time with no kick out danger. if your spacing is the same you can even notch the 6x6 slightly to aid in getting the new joists in. which since you only have one set you could.
If you've got time to order them or find a local supplier.
http://tinyurl.com/2uqo6g
ellis post jacks, they will work for you. I've used them in exactly the same situ, raise a rotted first floor, sistered new joists next to old, replaced sill and lowered back down. also in a crawlspace, just cut posts to length needed.
Trick "make a 1 1/2" wide by 1/2 to 3/4" deep notch centered at the top of the post" (keeps the 4x4 from turning when turning screw.)
Judo Chop!
If this is only floor joists and you are not jcking the wall or sill, thenthere is very little load on it at all. the teleposts would work. I typically don't use them for jacking,just for holding what is gained with a real jack, but for light loads, they will do.But there is another trick too that would work fine here.I am attaching some photos - they are not very clear, but should gtet the idea across.What you do is to nail a 2x6 up across the bottom of the joists. Then plumb down to lay another directly under that on the floor. Now cut some 2x6 studs so they are too longto fit between. You want them to lean at about 15°. Insert them in pairs as you see in thephotos to make A-frames. Jam them in tight. now once you have 3or4 ofthesse A-frames in place, you use them to start jacking.Reach around a pair with your belly against one and your hands grabing the other. Pull in so the bases slide towards each other, then let go. Repeat the process with each pair. Keep alternating until the joists are high enough, Then stab a duplex nail into the base of each one so it doesn't sklide out, and add a horizontal member at the waist of the A to stabilize them.In those photos, we jacked a ridge holding an entire roof that somebody had butcherd and was sagging 4-5inches. we've used this method half a dozen times for things like this and never had a failure. It is something you can do without equipment and one man can do it, though sometimes easier with two.
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