A question on basement jacks

[Perd Hapley]

My old, frame house has had a couple of post jacks down in the basement since back before I bought the place, and they happen to be where the water likes to go. Their bases are rusting, and I can already tell they're getting shorter. There happen to be three doors upstairs, in between where the two jacks are, and things aren't lining up anymore.

Should I just buy two new jacks? The jacks I see online have weight ratings. How do I know how much I need?

Or should I put in some more permanent supports?

For what it's worth, we've got a better handle on the water issues now, so I think I can avoid the rust problems. At least until I manage to unload the place on some other moron.

Suggestions?

[Hawkmoon]

The jacks I see online have weight ratings. How do I know how much I need?

The right answer is "Hire a structural engineer." The practical answer is that you can hold up the world with a 3-inch Lally column.

How many stories will these columns be holding up? One story, two stories, or two stories plus an attic? How wide is the house? How long is the house, and how far apart are the columns?

[KD5NRH]

The right answer is "Hire a structural engineer." The practical answer is that you can hold up the world with a 3-inch Lally column.

Agreed on both.  I forget what the actual yield strength of a piece of 6" H column loaded purely straight down is, but I remember thinking (after doing the math) that four of them holding up a 10" I beam made for an insanely strong replacement for a wooden structural wall we were taking out.  As in, we could have parked most of our heavy equipment on top of it and still had a huge margin as long as it was completely constrained laterally.  (Which it was, by a bunch of 1/4" wall 2x8 tubing with the other ends set in 12" thick concrete.)  2-3/8" drill pipe would have easily carried the weight, but we had the 6" left over from a project with a lot of waste that happened to include four 12' sticks.

[K Frame]

I believe that most jack posts are weight rated based on diameter of the post, diameter of the screw, and extension length (the shorter the screw the greater the weight load).

You should be able to measure all three aspects to see whats down there now.

If it's a case of just wanting to level up your floors it's less of a consideration.

If, however, you're attempting to provide structural support to an underbuilt or damaged house, then you really do want to consult an engineer.

My Mom's old house was built in 1903 and the living room floor had developed a sag as old houses are prone to doing, and the floor was swaying a bit when someone walked on it.

I determined the low point in the living room, then went to the basement and did some measuring across the sleepers. Essentially in was a case of the span being too long for the sleepers and over the years they had sagged a bit, so I got several jack posts and a couple of pieces of 2x6.

I scabbed the 2x6 together to form a beam, set it against the sleepers where I figured it would do the most good, and over the next several months very slowly raised the screws.

I made sure to measure at the ends of each end of the 2x6 beam to make sure that I was bringing the floor up evening.

It took about 6 months to raise the jacks to where where I wanted them to be. I raised them VERY slowly to allow the structure to acclimate to the changes and to hopefully prevent blowing plaster off the walls.

By the time I stopped, the floor in the living room was a LOT more even, the sag was pretty much gone, and the floor was no longer swaying when someone walked on it.



Just remember one rule of thumb... the more you extend the post, the less capacity rating it has.

One with a 4-8 to 8-4 adjustment range loses about half its load capacity when you get to 8 feet.

[lupinus]

What Hawk said.

The stubborn answer is try and figure it out yourself, and then buy the biggest Jack's you can muster anyway cause you probably screwed it up. But the biggest ones you can find will probably do it.

Have you considered detcord and/or fire as a more permanent solution?

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[Perd Hapley]

Have you considered detcord and/or fire as a more permanent solution?

Every time I pull into the drive.

[RoadKingLarry]

I'm right there with you. I'm kind of hoping for a tornado when we're not home. Much easier to sell to the insurance investigator.

[Ben]

Every time I pull into the drive.

 

[Perd Hapley]

I'm right there with you. I'm kind of hoping for a tornado when we're not home. Much easier to sell to the insurance investigator.

Because if you were home during the tornado, it might look like collusion?

[lupinus]

Because if you were home during the tornado, it might look like collusion?

I'm guessing he deals with enough flying monkies and people without brains that he doesn't want to have to deal with munchkins, long walks, and wizards too.

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[brimic]

This reminds me: I need to replace the pieces of galvanized tubing with proper jacks that the previous owner used to hold up the main beam in my barn

[Hawkmoon]

Rules of thumb to help you guesstimate the size/capacity of the jack columns you want to add:

I assume you want to shore up the main carrying beam that runs along the center of the house. The floor joists all have one end bearing on this beam and the other end bearing on the exterior foundation wall. In general, half the weight goes to the center beam, and half the weight goes to the exterior foundations. Say the house is 24 feet deep and 30 feet long. That means the center beam is supporting a floor area that's 12 feet wide by 30 feet long.

How much weight? A conservative number is that the weight of the floor construction (the "dead load") runs 10 pounds per square foot. For residences, building codes call for a "live load" (that's everything you put on top pf the floor -- people, pets, furniture, and "stuff") of 40 pounds per square foot for the first floor, and 30 pounds per square foot for the upper floors. To calculate the load on a center beam for a one-story house, add the dead and live loads and you get 50 pounds per square foot. The house -- and beam -- is 30 feet long. Each foot of the beam supports a 12-inch strip that's 12 feet long, or 600 pounds.

How far apart are the posts? If they're spaced 10 feet apart, each one holds up 10 feet worth of the floor load. At 600 pounds per foot, each post has to support 6,000 pounds. Reduce the spacing to 5 feet and each post carries 3,000 pounds.

[KD5NRH]

One thing I have seen done with this type of situation was to bolt heavy 8" C channel along both sides of the beam right in the middle before jacking.  Once it was jacked (slowly) to just a hair over exactly right, through bolts were added about 18" apart down the length of the beam.  Thus, in the end, the floor had a wooden beam sandwiched between two very rigid steel sections, and a couple of square tube posts were welded in place over footers that went to (reasonably shallow - 6-8' as I recall) bedrock.

That was a historic building that needed to stand indefinitely, though, so it might not be a reasonable solution for a less historically important house that someone might want to tear down in the foreseeable future.  Not insanely expensive - just a couple 30' C channels and some 4x4x1/4" square tube, so a few hundred in steel, but the cost of removing it for demolition would be substantial.  They also had the advantage of a large door/ramp to the basement, so the footers could be augered most of the way down rather than having to hand dig all the way, and concrete was piped in instead of hand mixed and poured.  If the span is short enough and existing supports strong enough, you could probably do away with the extra posts and have something more practical for a residential repair.

[K Frame]

"That was a historic building that needed to stand indefinitely, though, so it might not be a reasonable solution for a less historically important house that someone might want to tear down in the foreseeable future."

Now don't be too hasty. I'm sure that at some point in the future we'll see a Museum of Fistful dedicated at that site.

[KD5NRH]

Now don't be too hasty. I'm sure that at some point in the future we'll see a Museum of Fistful dedicated at that site.

They'll need to build ten subbasements to hold the records of the stuff that's his fault.

[Perd Hapley]

I'm going to get some of these from Menards.

https://www.menards.com/main/building-materials/posts-columns/steel-columns/3-adjustable-columns/m200/p-1444423420357.htm

The idea is, after the proper adjustments have been made, you pour concrete around the base. Would it be a good idea to drill into the floor, and put in some rebar, to lock into the new concrete base?

I'll take my answer off the air.

[Hawkmoon]

I'm going to get some of these from Menards.

https://www.menards.com/main/building-materials/posts-columns/steel-columns/3-adjustable-columns/m200/p-1444423420357.htm

The idea is, after the proper adjustments have been made, you pour concrete around the base. Would it be a good idea to drill into the floor, and put in some rebar, to lock into the new concrete base?

I'll take my answer off the air.

Are you planning on installing them as in the photo, so the adjusting screw will end up buried in the concrete you're going to pour? I've never seem them used in that orientation for a permanent installation, and rarely even for temporary. I'd put the screw on the upper end, which allows for adjustment in the future if there's settlement.

I probably wouldn't bother with the concrete. I'd buy a 1/2" concrete drill bit and drill a couple of anchor bolt holes for each one, then use wedge anchors.

https://www.menards.com/main/tools-hardware/fasteners-fastener-accessories/anchors/wedge-anchors/midwest-fastener-reg-1-2-x-2-3-4-hex-nut-wedge-expansion-anchor-10-count/50385/p-1444439865697-c-8727.htm?tid=3922568177236538756&ipos=7

[Perd Hapley]

Are you planning on installing them as in the photo, so the adjusting screw will end up buried in the concrete you're going to pour? I've never seem them used in that orientation for a permanent installation, and rarely even for temporary. I'd put the screw on the upper end, which allows for adjustment in the future if there's settlement.

OK, I hadn't thought of the settling issue.

I would have thought the adjustment went on top, mainly because it would be easier to adjust, but not as likely to be accidentally bumped. I think they're putting the adjustment on the bottom, so it can be encased in concrete.

Thanks for the suggestions.

Also, the posts in my basement currently are the two-piece variety, with just a single pin keeping them together.  I'm pretty sure a solid adjustable will be a better support than those things.

[RocketMan]

We used a couple of jack posts similar to these Akron Big Moe jack posts from Lowe's in the basement of our house. They worked really well augmenting some existing jacks to fix a sagging floor in the SW corner of the house.
We put the adjustable part of the jack under the floor joists, not against the concrete floor as that was how all the original jacks had been installed by the home builder.  The jacks are rated at 9,000 lbs compression load at full eight foot extension.  A shorter extension allows a higher compression load.
The two cross pins are actually 5/8-16 steel bolts IIRC.  I put nylock nuts on mine (or the posts came with them, I disremember).

[Triphammer]

It looks from their instructions that these would be new work/ original columns.  Setting them before the floor is poured. As repair jacks I'd want the screw on top. If it settled once it'll settle more. You do want to put them on concrete or steel  pads as  you want to spread the weight over a larger area over the 3 or 4" concrete that makes up most of the floor. original columns are set on or in pads or footers before the floor is poured

[Hawkmoon]

Fistful, are you going to temporarily shore up the carrying beam and put the new jacks where the originals are/were, or will the new ones go in supplemental locations? As Triphammer commented, the originals should have footing pads under the slab, so if you replace in the original locations you don't need more concrete. But you should install a couple of anchor bolts to prevent shifting of the post base plates.

[K Frame]

I would not embed the post in concrete. The concrete over time will wick water and it will rust out the column. I've never found a need to anchor the base to the concrete because once you put some stress on it with the weight of the house bearing down on it it is not going anywhere. If anything, I would suggest putting some sort of waterproof barrier under the column base. Doesn't have to be much. Just something like a sheet of vinyl flooring.

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[Perd Hapley]

If anything, I would suggest putting some sort of waterproof barrier under the column base. Doesn't have to be much. Just something like a sheet of vinyl flooring.

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I've been thinking about something like that, too, but if I used a footing pad, I would think that would take care of it. But what kind of footing pad? 

[Hawkmoon]

On highway bridges, one end of each span has to be free to slide to allow for thermal expansion and contraction. I'm pretty certain the bearing pads are Teflon. But I don't know if all Teflon is created equal, or if there's a "structural grade" Teflon for load-bearing applications.

[Perd Hapley]

On highway bridges, one end of each span has to be free to slide to allow for thermal expansion and contraction. I'm pretty certain the bearing pads are Teflon. But I don't know if all Teflon is created equal, or if there's a "structural grade" Teflon for load-bearing applications.

I think they outlawed those cop-killer footing pads.