A jack post is an adjustable steel column used to support beams, joists, and ceilings during construction or repair work.
If you’re dealing with a sagging floor, planning a basement remodel, or bracing a wall during a renovation, you’ve likely run across the term. A jack post—sometimes called an adjustable steel column, telepost, or screw jack—is a telescoping steel support that transfers heavy structural loads down to a solid surface. It’s not decorative hardware; it’s load-bearing equipment with real engineering behind it. The sections below cover what these posts do, how they’re built, and the mistakes that get people into trouble.
What Does a Jack Post Do?
A jack post provides structural support for beams, joists, ceilings, walls, and even formwork during concrete work. Contractors use them for temporary shoring—propping a beam up while a post or wall is replaced—and for permanent installations in basements and crawlspaces where a load-bearing wall doesn’t exist. Home Hardware describes its JP96 jack post as being used to support carport roofs and beams carrying loads not more than two wood-frame floors, with joists not exceeding 16 feet and a live load that doesn’t exceed 50 pounds per square foot. That specification shows how narrowly these products are engineered: the right post for a carport beam may be entirely wrong for a three-story column.
How a Jack Post Is Built
Most jack posts share the same basic anatomy: a double-tubed telescopic steel column, an inner tube and outer tube, plus a threaded adjustment screw and bearing plates at both ends. Setting one up involves raising the post to its approximate height, then fine-tuning with a threaded handle or wrench. Some models use a locking-pin system with holes drilled at set intervals, while others use a locking ring that slides along the barrel.
Steel gauge varies by model and intended duty. A Peak Adjustable Steel Jack Post sold in Canada lists an 11-gauge outer and inner tube, while another retail model uses a 12-gauge outer with an 11-gauge inner. Consumer-grade Tiger Brand posts can use 15-gauge steel. Lower gauge numbers mean thicker steel, and thicker steel generally means a higher load rating—but only up to the limits the manufacturer documents.
Where the CCMC and CGSB Fit In
In Canada, building codes and inspectors recognize jack posts through the Canadian Construction Materials Centre (CCMC), an agency under the National Research Council. The Peak model mentioned above carries CCMC evaluation number 13639-L and conforms to CAN/CGSB-7.2-94, a standard for steel building columns. That CCMC evaluation applies only for imposed loads not exceeding 36 kilonewtons (kN)—a hard ceiling set by the National Building Code of Canada 2015. If you’re in the U.S., you’ll more often see load ratings in pounds, and state or local building codes generally govern which products are acceptable. Always match the post to the code that applies where the work happens.
Load Ratings: Why the Same Post Isn’t a One-Size-Fits-All Tool
The single most misunderstood thing about jack posts is that load capacity changes with extension. That’s not a manufacturing flaw—it’s basic physics. A longer, more extended column has more leverage and a greater tendency to buckle under load.
The real-world numbers from cited products tell the story:
| Model / Product | Height Range | Max Load at Max Extension |
|---|---|---|
| CCMC Model 2312 | Up to 32 in | 8,090 lb |
| CCMC Model 2313 | Up to 55 in | 8,555 lb |
| CCMC Model 2314 | Up to 100 in | 11,650 lb |
| Tiger Brand J-S-55 | Retail examples to ~96 in | Up to 20,400 lb (model dependent) |
| Peak / CCMC 13639-L | Range varies | 36 kN ceiling (per CCMC eval) |
The pattern holds across brands: allowable loads drop as the post extends. When you plan a job, look up the rating at your installed height, not just the “max capacity” number on the box.
Common Mistakes and Safety Caveats
Four errors show up again and again on job sites and in DIY forums:
- Treating all jack posts as interchangeable. A post rated for 8,000 pounds will fail if you put 15,000 on it. Load, height range, and code compliance vary widely by model, and swapping one for another without checking specs is a gamble no one should take.
- Ignoring the reduced rating at greater extension. Max load at shortest height means nothing if you need it fully extended.
- Using a post outside its code scope. The MITEK JP96 has explicit limits on floor count, joist span, and live load. So do most others. A post that’s fine for a single-story carport isn’t automatically rated for a two-story house.
- Confusing jack posts with lally columns. A lally column is a specific type of support column (traditionally concrete-filled steel pipe). “Jack post” is often used loosely to mean any adjustable metal column, but the underlying product ratings and documentation matter more than the name. Read the spec sheet before you buy.
Using a post outside its documented building-code scope or application limits isn’t just risky—it can fail inspection and put lives at risk.
If you’re ready to buy and need to compare options side by side, check out our tested roundup of the best basement jack posts for what actually holds up on the job.
FAQs
Can a jack post support a permanent load?
Yes, many jack posts are permanently installed in basements and crawlspaces, but “permanent” must mean permanently within the manufacturer’s rated limits. A telescoping steel column left in place for decades can support a beam indefinitely as long as the load never exceeds the documented rating at that exact height and the post is set on a proper concrete footing or base plate with adequate bearing capacity.
What’s the difference between a jack post and a lally column?
A jack post is an adjustable, telescoping column that changes height by spinning an inner threaded screw. A lally column is a pipe column, historically filled with concrete, that’s cut or cast to a fixed length. In practice, the terms blur in consumer catalogs, but the critical difference is documentation: a real lally column carries a structural rating based on the steel pipe and concrete fill, not an adjustable mechanism.
How much weight can a standard residential jack post hold?
The only number that matters is the one listed at your installed extension height.
References & Sources
- National Research Council Canada (CCMC). CCMC Evaluation 13639-L Details the 36 kN maximum allowable working load for Peak model under NBC 2015.
- Tiger Brand Jack Post. Tiger Brand Jack Post Catalog 2021 Provides model-specific load ratings, steel gauges, and application guidance.
- Wikipedia. Jack Post General background on adjustable steel column terminology and construction.
