Thoughts on leaving adjustable steel jacks as permanent support?

I’ve spent plenty of time cranking on those Tiger Brand jacks to level out old 1920s floor joists, and they definitely have thier place for temporary fixes or incremental lifting. However, leaving them in as the permanent solution always makes me a bit uneasy. In my experiance, those screw threads are a potential weak point over several decades, especially if there is any basement humidity that leads to surface rust or seizing. When I did the structural work on my last renovation, I used the adjustable posts to get the 2x12 headers exactly where they needed to be, but then I cut 6x6 Douglas fir posts to size and swapped them in. I prefer having a solid wood-on-wood connection with a heavy-duty Simpson post base anchored into the concrete. It eliminates the worry about the steel bowing or the adjustment mechanism failing. Even if the house settles, I'd rather shim a wood post than trust a thin steel tube to carry the load for the next fifty years.

I actualy prefer the adjustable steel columns, especally in these older renovations where you know the foundation hasn't finished moving. I’ve used the Mono-Post brand in several crawlspace jobs becasue wood posts can be a nightmare to shim perfectly. If you have a 2x12 header and you cut a 6x6 wood post just a hair short, you're stuck using thin shims that eventually compress or rot. With a heavy-duty screw jack, you get that exact tension right from the start. As for the corrosion worry, as long as you aren't dealing with standing water, a high-quality powder-coated post is going to outlast us all. I’ve pulled out 50-year-old Lally columns that were still structural, even with a bit of surface scale. In my neck of the woods, the ability to give the screw a quarter-turn five years down the line when the new lumber finally dries out and shrinks is a massive advantage. I’d rather have that adjustability than a permanent wood post that leaves a gap at the top once the moisture content drops from 15% to 8%.

I remember back when we wouldn't trust those skinny screw jacks for anything but a temporary prop while we poured a real footing. If you're leaving steel in, it ought to be a real lally column—the kind we used to fill with concrete right on site. Those thin-walled adjustable ones you see nowadays don't have the bearing plate surface area to keep from punching right thru an old thin slab over time. I’ve seen 'em move an inch down into the floor while the house stayed put. If they didn't beef up the footer under that jack, they're asking for trouble regardless of how beefy those 2x12s look.

I'm still a total rookie at this, but seeing those steel jacks under big 2x12s makes me wonder about the connection point. If you use the steel ones, how do you acutally keep the wood from sliding off the top plate? It seems like it whould be slippery compared to wood-on-wood. Is there a special bracket you're supposed to use to bolt them togather, or does the weight of the house just hold it all in place? I'd be terrified of it shifting an inch and everythign coming down.

I've had luck with the 'hybrid' approach on my own projects. I usually set the screw jacks to get everything level, then I'll sandwich them between two 2x6s that I've custom-cut to fit tight under the header. I basically use the steel as a core but let the wood take the actual weight once the house settles. It stops that 'slippery' feeling and gives me more surface area to nail into. Never liked the look of just a skinny pole holding up my kitchen floor, and this way I don't have to worry about the threads rusting out or failing down the road.

While the previous points regarding axial load and plate surface area are technically sound, I find it quite pertinent to consider the specific metallurgical degradation that occurs when a high-carbon steel screw assembly remains in direct contact with the moisture-laden environment of a sub-grade crawlspace. Even if one justifies the use of these adjustable columns for their leveling convenience, the lack of a proper lateral restraint system at the top plate often fails to address the potential for eccentric loading, which could induce a catastrophic buckling failure if the vertical alignment is even a fraction of a degree off-center. I personally prefer to verify the exact gauge of the steel tube, as many of those off-the-shelf jacks are surprisingly thin-walled compared to a true schedule 40 pipe.