For most basement beams, a steel column is the more compact, durable and predictable choice, and a wood post is a legitimate alternative where it meets the code's minimum size and is kept off damp concrete. The 2024 Ontario Building Code sets a minimum of 140 mm x 140 mm for rectangular wood columns (184 mm if round), while a steel pipe column can be as small as 73 mm in outside diameter with a 4.76 mm wall. That size difference, plus moisture, is what usually decides it.
"Lally column" is the US name for a steel pipe column, often filled with concrete. In Ontario, basement columns are usually teleposts, fixed steel pipe columns or HSS posts. This post compares steel columns as a group with solid, built-up and glulam wood posts.
What the Ontario Building Code says about each
Section 9.17 of the 2024 OBC (O. Reg. 163/24) covers columns in houses and small buildings. It sets separate rules for steel and wood:
| Requirement | Steel columns | Wood columns |
|---|---|---|
| Minimum size | Pipe: 73 mm outside diameter, 4.76 mm wall (9.17.3.1.) | 140 mm x 140 mm rectangular or 184 mm round, and not less than the width of the supported member (9.17.4.1.) |
| Smaller sizes allowed? | Yes, where loadbearing capacity is shown to be adequate | Yes, where calculations show lesser sizes are adequate |
| Ends | Plates at least 100 mm x 100 mm x 6.35 mm each end; top plate spans the full width of a wood beam (9.17.3.2.) | Bearing as designed and detailed |
| Material | Steel pipe or other sections; adjustable columns to CAN/CGSB-7.2 up to 36 kN (9.17.3.4.) | Solid, glued-laminated or built-up (9.17.4.2.) |
| Contact with concrete | Exterior columns need rust-inhibitive paint (9.17.3.3.) | Separated from concrete in contact with the ground by 0.05 mm polyethylene or Type S roll roofing (9.17.4.3.) |
| Built-up columns | Not applicable | 38 mm members, bolted with 9.52 mm bolts at no more than 450 mm or nailed with 76 mm nails at no more than 300 mm (9.17.4.2.) |
Both types must be centred on a footing that conforms to Section 9.15 and fastened to the member they support (Articles 9.17.2.1. and 9.17.2.2.). Section 9.17 applies to columns under beams carrying up to two wood-frame floors with a supported joist length of 5 m or less; outside that, columns are designed under Part 4. Our guide to lally column footing requirements covers the footing side.
Lally column vs 4x4 and 6x6 posts
This is the most common version of the question, and the code answers it directly.
- 4x4 (89 mm x 89 mm dressed). Below the 140 mm x 140 mm minimum for a rectangular wood column. Under Part 9, a 4x4 can only be used as a basement column if calculations show it's adequate. A 4x4 also can't match the width of a typical built-up beam, which the code requires.
- 6x6 (140 mm x 140 mm dressed). Meets the minimum size for a rectangular wood column. It still has to be at least as wide as the beam it supports, so a beam made of four 38 mm plies (152 mm) is wider than a 6x6.
- Steel pipe or HSS. Meets Part 9 at 73 mm outside diameter and 4.76 mm wall, or larger sections where the designer sizes them. Square and rectangular HSS posts are common on engineered drawings; see our HSS sizes chart.
Meeting the minimum size is not the same as carrying the load. A column's capacity depends on the load from above, its height and how it's braced. Your designer confirms what's adequate.
Strength and space
Steel is much stronger and stiffer than wood for its size, so a steel column carrying the same load is far slimmer. In a basement that's being finished, that's often the deciding factor: a slim steel post can be boxed in to a narrow column or left exposed and painted, while a wood post sized for a heavy load gets bulky.
Height matters too. Tall, slender columns are more likely to buckle, so a longer post needs a bigger section to carry the same load. In a lowered or high-ceiling basement, that can push a wood post to a size that is awkward to fit or finish around, which is where steel's smaller footprint helps.
Moisture, rot, insects and rust
Basements are damp, and this is where steel and wood fail differently.
Wood posts can rot at the base if they sit on or near damp concrete. That's why the code requires a separation layer between wood columns and concrete in contact with the ground. Where termites are known to exist, exterior wood columns, such as porch posts, need pressure treatment or a non-cellulosic base that keeps them clear of the ground (Article 9.17.4.4.). Wood also shrinks as it dries, which can open small gaps at the top of a new post.
Steel posts don't rot, shrink or attract insects, but they rust if they sit in water. A post standing in a wet corner, or one whose base plate is buried in a damp slab patch, should be painted and kept dry. Look for flaking or pitting at the base when you inspect.
In a dry, finished basement, either material lasts. In a basement with a history of water, steel with a good coating, or wood with proper separation and drainage, both need attention to the base detail.
Connections and installation
Steel columns are cut to a measured length and come with welded base and cap plates. The cap plate is bolted or screwed to a wood beam, or bolted or welded to a steel beam. Fixed posts need an accurate field measurement because they can't be trimmed easily on site. Adjustable steel columns (teleposts) avoid that but have their own load and labelling rules; see can adjustable steel columns be permanent.
Wood posts are easy to cut and fit on site with ordinary tools, and they fasten naturally to a wood beam with connectors. They're the simpler option when a carpenter is already framing and the beam is wood.
Mixing materials is common: a steel post under a built-up wood beam, with the top plate spanning the beam's full width as the code requires. A wood post under a steel beam is less common and needs a detailed connection.
Lally column vs wood post: which to choose
| Situation | Usually a better fit |
|---|---|
| New steel beam in an engineered basement renovation | Steel post, as detailed by the engineer |
| Finished basement where you want slim columns | Steel post |
| Damp basement or post near a floor drain | Steel post with a good coating, kept dry |
| Light load under a wood beam, carpenter on site | Wood post at or above code minimum, on a separation layer |
| Replacing an undersized 4x4 | Either, sized by a designer |
| Exterior deck or porch columns | Either; termite and corrosion rules apply |
Both must sit on a proper footing, and changing, adding or removing a column is a structural alteration that needs a designer and usually a building permit. Never remove a post without temporary support for the beam. If you're replacing columns, our post on the cost to replace or remove a lally column explains what drives the job.
Steel posts made to length
We fabricate HSS and steel posts for basements with base and cap plates welded on, cut to your measured length and drilled for the beam connection, along with the beams and plates they support. Send your drawings or measurements for a quote, or see our steel products.
Frequently asked questions
Is a steel column better than a wood post?
Neither is better in every case. Steel posts are slimmer for the same load, do not rot, shrink or get eaten by insects, and are the usual choice under steel beams. Wood posts are easy to cut and fasten on site and suit wood beams, as long as they meet the code's minimum size and are kept off damp concrete.
Can I use a 4x4 instead of a lally column?
Not as a basement column under Part 9 unless calculations show it is adequate. The 2024 Ontario Building Code requires wood columns of at least 140 mm x 140 mm if rectangular or 184 mm if round, and at least as wide as the beam they support. A 4x4 is 89 mm x 89 mm.
Is a 6x6 post as good as a lally column?
A 6x6 (140 mm x 140 mm dressed) meets the Part 9 minimum size for a rectangular wood column, but meeting the minimum does not mean it carries the same load as a given steel column. Whether either one is adequate depends on the load and height, which your designer checks.
Do wood posts on a basement floor need protection?
Yes. Wood columns must be separated from concrete in contact with the ground by 0.05 mm polyethylene film or Type S roll roofing (Article 9.17.4.3.). They also need to sit on a proper footing, like any column.
