A lally column is the steel pipe column that holds up the main beam in a basement. The name is generic now, but it covers two different products: a fixed-length pipe column, usually concrete filled, that is cut to size and permanently installed, and an adjustable screw column, often called a jack post, that threads up and down.
The difference matters, because one of them is designed to be a permanent structural support and the other is frequently installed as one when it should not be.
What a Lally Column Actually Is
The original lally column is a round steel pipe filled with concrete. The pipe carries the load and confines the concrete; the concrete stiffens the pipe and helps it resist buckling. The column sits on a footing, usually a thickened pad under the basement slab, and carries a cap plate at the top where the beam bears.
That load path is worth following all the way down. The beam collects floor loads, the column collects the beam reaction, and the footing spreads that point load into the soil. Skip the footing and you have concentrated several tons onto a slab that was never designed for it.
Lally Column vs Adjustable Jack Post
These get used interchangeably in conversation and they are not the same thing.
| Fixed lally column | Adjustable column (jack post) | |
|---|---|---|
| Length | Cut to fit, then set | Threaded screw, adjusts over a few inches |
| Fill | Often concrete filled | Hollow |
| Intended use | Permanent structural support | Depends entirely on the product |
| How capacity is established | Engineering calculation for the pipe and its length | Rated load from the manufacturer’s evaluation report |
| Typical failure mode | Corrosion at the base, undersized footing | Overloading a light-duty post, or using a temporary one permanently |
The important point about adjustable columns is that some are made and listed as permanent structural supports and some are sold as temporary shoring. The permanent ones are evaluated against acceptance criteria and carry an evaluation report number. Tiger Brand, for example, references ICC-ES evaluation report ESR-1766 and states on its adjustable steel column page that the columns comply with the IBC and IRC (checked September 2026). A light-duty post from the hardware store aisle with no listing behind it is not the same product, even though it looks similar.
If a column is holding up your house rather than propping something during work, look for the marking on the post and the evaluation report behind it.
What Actually Governs Capacity
A column does not fail by crushing. It fails by buckling, and buckling depends on far more than the diameter of the pipe.
Unbraced length
The distance between the points where the column is held in position. A taller column of the same diameter carries less. This is why the same product is rated differently at different heights, and why a column in a high basement is not interchangeable with one in a low crawl space.
Diameter and wall thickness
Both matter, and wall thickness is the one people forget. Two posts can measure the same across the outside and have very different walls. Gauge is a thickness designation rather than a dimension, which is a recurring source of confusion; our steel gauge thickness guide covers how gauge numbers map to real thicknesses.
End conditions
Whether the top and bottom are genuinely held against sideways movement changes the effective length, and effective length drives the capacity. A cap plate bolted to the beam behaves differently from a post wedged underneath it.
What is above it
The column only has to carry what the beam delivers to it, which depends on the beam, the spans either side, and the floor loads. If you are sizing the beam as well, the section properties in our wide flange beam sizes chart are the starting point, and the steel beam weight calculator gives you the beam’s own weight for the total.
None of this is a do-it-yourself calculation. A licensed structural engineer has to establish the load and size the column and its footing for your specific house.
Where Lally Columns Go Wrong
Rust at the base
This is the classic one. The bottom few inches sit where water collects, and the pipe rusts from the outside in. The column can look sound at eye level and be significantly thinner at the floor. Scale flaking off the base, a ring of rust staining on the slab, or a base plate that has lost its edges are all worth a closer look. Coatings help; our guide to whether galvanized steel rusts explains what a zinc coating does and does not do once it is scratched or sitting in standing water.
No real footing
A column added later, during a finishing project or a repair, is often set straight onto the slab. It may hold for years and then punch through, or settle slowly and let the floor above sag back down.
A temporary post left in place
Screw jacks used to prop during work sometimes never come out. They were sized for a short-term prop, not a permanent load, and they are usually not listed for it.
Out of plumb
A leaning column is carrying its load eccentrically, which is a different and worse problem than a straight one. It usually means something moved, so the question is what moved and why.
Replacing or Adding a Column
Replacing a basement column is not a swap. The load has to be carried on temporary shoring while the old column comes out, the footing usually has to be exposed and often enlarged, and the new column has to be set plumb and connected top and bottom. Getting the temporary support wrong is the dangerous part, because you are deliberately removing a support from a loaded structure.
The same logic applies when a column is going in because a wall is coming out. That is a load path change, not a cosmetic one, and it is covered in our guide to removing a load bearing wall.
Expect a permit and an inspection in most jurisdictions. Both are in your favor here: they put a second set of eyes on the footing, which is the part nobody can see once the work is done.
Lally Column FAQ
Why is it called a lally column?
It comes from a brand name for concrete filled pipe columns that became the everyday term, in the same way people say a generic name for a product category. Today it is used loosely for almost any steel basement column.
Can I use an adjustable jack post permanently?
Only if that specific product is listed for permanent structural use and is installed within its rated conditions, on a proper footing. Many are not. Check the marking on the post and the evaluation report number, and have the load checked rather than assuming.
How much weight does a lally column hold?
There is no single number. Capacity depends on diameter, wall thickness, unbraced length and end conditions, so the same post is rated differently at different heights. For a listed adjustable column the rated load comes from the manufacturer’s evaluation report; for a fixed column it comes from a calculation.
Should a column be filled with concrete?
Filling increases stiffness and buckling resistance, which is why traditional lally columns are filled. It is not automatically required. What matters is that the column as built has been shown to carry the load it is under.
Is surface rust on a basement column a problem?
Light surface rust on the shaft usually is not. Section loss at the base is. If the steel is flaking, pitted, or sounds hollow when tapped near the floor, get it looked at rather than painted over.
The Short Version
A lally column is the pipe column under your main beam. Fixed columns are permanent by design; adjustable posts are only permanent if that product is listed for it. Capacity is driven by unbraced length and wall thickness as much as diameter, the footing matters more than the column, and the base is where they fail. Any change to one is a change to the load path, so it belongs to a licensed structural engineer rather than a guess.
Reference information only, not engineering advice. Disclaimer.