A lally column is a steel pipe column that supports a girder, usually in a basement. Under 2021 IRC Section R407.3, a steel column must be at least 3-inch-diameter Schedule 40 pipe and be restrained against lateral movement at its bottom end.
"Lally" began as a trade name and is now used for any round steel support post, often filled with concrete. The code never uses the word. It says "steel column" and applies the same section to every steel column in a house, whatever the brand. Below: what the code requires, how the post is anchored, and where it goes on a framing plan.
Key facts
- A steel column must be not less than 3-inch-diameter Schedule 40 pipe made to ASTM A53/A53M Grade B or an approved equivalent (2021 IRC Section R407.3).
- A wood column must be not less than a nominal 4 inches by 4 inches (2021 IRC Section R407.3).
- Every column must be restrained to prevent lateral displacement at the bottom end (2021 IRC Section R407.3).
- All inside and outside surfaces of a steel column need a shop coat of rust-inhibitive paint, unless the steel is corrosion resistant or coated for corrosion resistance (2021 IRC Section R407.2).
- A footing under a column is sized from the tributary load and the allowable soil pressure, and no concrete footing may be less than 12 inches wide and 6 inches deep (2021 IRC Section R403.1.1).
- Girder ends need at least 3 inches of bearing on masonry or concrete, and at least 1-1/2 inches on wood or metal (2021 IRC Section R502.6).
What is a lally column used for?
A lally column is a vertical support that picks up a girder at a point between walls, so the floor joists above can span shorter distances. In a basement the girder usually runs down the middle of the house. The joists bear on it from both sides, and the columns under it carry the combined load to footings in the slab or ground.
Each column is a concentrated load path. A single post can carry a large share of the floor, which is why the footing under it matters as much as the pipe. For how a column fits the wider drawing, see the structural grid and columns primer and the load-bearing walls guide.
What is the minimum size for a steel support column?
The minimum is 3-inch-diameter Schedule 40 pipe to ASTM A53/A53M Grade B, or an approved equivalent, under 2021 IRC Section R407.3. That is a floor for the pipe only. It does not say how much load a particular column can carry, and the code text does not give a load table for columns.
A longer column, a heavier girder load, or a higher floor load can require a larger section or an engineered design. The same section also covers wood columns, which must be not less than a nominal 4 inches by 4 inches.
Minimum column sizes, 2021 IRC Section R407.3.
| Column type | Minimum size in the code |
|---|---|
| Steel | 3-inch-diameter Schedule 40 pipe, ASTM A53/A53M Grade B or approved equivalent |
| Wood | Nominal 4 inches by 4 inches |
How is a lally column restrained at the top and bottom?
The code requires restraint at the bottom end only: the column must be restrained to prevent lateral displacement there (2021 IRC Section R407.3). In practice that means the base is located on the footing or slab with a plate, anchor, or similar detail so the post cannot kick out.
One exception exists. In Seismic Design Categories A, B and C, a column not more than 48 inches high on a pier or footing is exempt from the bottom-end requirement, but only within an under-floor area enclosed by a continuous foundation. A column that exceeds that height, or sits outside such an enclosed area, is not exempt.
At the top, the code section is silent on the connection. The girder normally sits on a cap plate, and the plate is fastened to the girder in whatever way the plans or engineer specify. Do not guess the fasteners from a forum post. Where the girder is wood, bearing and connection are drawn on the structural details.
What does a lally column bear on?
A lally column bears on a concrete footing, and 2021 IRC Section R403.1.1 sizes that footing from the tributary load and the allowable soil pressure in Table R401.4.1. The tributary load is the share of the floor and walls above that this one column collects.
Footing rules to know:
- Concrete footings may not be less than 12 inches wide and 6 inches deep (R403.1.1).
- Footing projections may not be less than 2 inches and may not exceed the footing thickness (R403.1.1).
- Footings sit on undisturbed natural soils or engineered fill (R403.1).
The footing is under the slab, so it is easy to forget. If a column is being added or moved, the new location needs its own footing, not just a new post on the existing slab. Where a masonry pier carries the girder instead of a column, R404.1.9.2 gives a minimum nominal dimension of 12 inches and a maximum pier height of 10 feet for interior bearing walls, or 4 feet for exterior bearing walls, from top of footing to bottom of the sill plate or girder.
How does the girder sit on the column?
Section R502.6 requires the ends of each joist, beam or girder to have not less than 1-1/2 inches of bearing on wood or metal, or not less than 3 inches on masonry or concrete, or to be supported by approved hangers. A column cap plate is metal, so the 1-1/2 inch figure is the one that applies at the top of a steel column.
Girder size comes from tables, not from the column. Section R502.5 sends dimension-lumber girders to Tables R602.7(1) and R602.7(2), covered in the header size chart. Those tables limit girder span, so the column spacing along the girder is a design decision made together with the girder size.
Lally column vs wood post vs adjustable steel post
The three differ in code treatment, durability, and approval.
| Type | Code position | Main concern |
|---|---|---|
| Steel pipe column (lally) | Minimum 3-inch Schedule 40 pipe, shop-coated against rust (R407.2, R407.3) | Rust, base restraint |
| Wood column | Minimum nominal 4 by 4 (R407.3), protected against decay under R317 (R407.1) | Decay at the base |
| Adjustable steel post (screw jack) | Manufactured product, used under manufacturer's instructions | Whether the product is accepted for permanent support |
Wood columns have a specific moisture rule. Section R317.1 requires naturally durable or preservative-treated wood for wood columns closer than 8 inches to exposed ground in a crawl space, and for wood columns in contact with a basement slab unless they sit on a concrete pier or metal pedestal projecting at least 1 inch above the floor with a moisture barrier between.
An adjustable steel post, often called a screw jack post, has a threaded section so the height can be set. These are listed or evaluated products, and their rated load comes from the manufacturer, not from the IRC. Whether one is acceptable as the permanent support is a question for the manufacturer's instructions, the product listing, and the building department.
Where lally columns go on a framing plan
On a floor framing plan, a basement column appears as a symbol on the girder line, tagged and tied to a schedule or note. Spacing along the girder follows the girder's allowable span. Each column should line up with a footing shown on the foundation plan, and with the support above it if the load continues upward.
A column symbol on one level does not prove support continues below, so check the foundation sheet. The framing plan symbols guide shows how columns are usually drawn. A pier and girder line also needs to agree with the joist direction you chose, since the joists bear on it. The floor joist span table shows how girder position changes joist length.
Can I replace or remove a lally column?
Treat a column as structural until an engineer says otherwise. Removing, moving, or swapping one changes the load path through the girder, the floor above, and the footing.
- Temporary shoring must carry the girder before the old column comes out.
- A new column location needs its own footing, sized from the tributary load.
- A replacement column or beam is designed by an engineer, and most jurisdictions require a permit and inspection.
- A same-size swap of a corroded pipe still needs shoring and a check of the base.
What the code text does not cover
Section R407 gives minimums. It does not give load capacities, column heights, concrete fill requirements, cap and base plate sizes, or fastener schedules. Those come from the plans, the engineer, or the manufacturer. The adopted code edition and local amendments govern, and this page is a general guide, not a design.
Summary
A lally column is a steel pipe column, and the 2021 IRC requires at least 3-inch-diameter Schedule 40 pipe, a shop coat of rust-inhibitive paint, and restraint against lateral movement at the bottom end. It bears on a concrete footing sized from the tributary load and soil pressure, never smaller than 12 inches by 6 inches. Adjustable posts are manufactured products used under the manufacturer's instructions, and any column change needs shoring and an engineer.
Open the framing studio to draw the girder line and column positions on a preliminary framing plan. Framing Plan draws joist layouts, beams and openings and exports PNG, PDF and DXF. It does not size columns or check them against the code, so confirm every column with your designer or plan reviewer.