Basement columns in Ontario houses are governed by Section 9.17. of the 2024 Ontario Building Code. A steel pipe column needs an outside diameter of at least 73 mm and a wall of at least 4.76 mm, with a steel plate at least 100 mm × 100 mm × 6.35 mm at each end. Every column must be centred on a proper footing and fastened to the beam it supports. Adjustable steel columns (teleposts) must conform to CAN/CGSB-7.2 and carry no more than 36 kN, and anything outside these rules has to be designed under Part 4.
"Lally column" is a US term for a steel pipe column, often concrete filled. The Ontario code doesn't use the name. It simply has rules for steel, wood, masonry and concrete columns, which are set out below.
When the Part 9 column rules apply
Section 9.17. doesn't cover every column in a house. Under Article 9.17.1.1., it applies to columns supporting:
- Beams carrying loads from not more than 2 wood-frame floors, where the supported length of joists bearing on the beam doesn't exceed 5 m and the live load on any floor doesn't exceed 2.4 kPa
- Beams or header joists under decks, balconies and similar exterior platforms, within limits on levels, joist length and loads, where the platform serves only one residential suite
- Carport roofs
That covers the basement columns in most single-family houses. Columns that fall outside it, for example under a beam carrying concentrated loads, a third floor, or long-span joists, must be designed under Part 4. In practice that means an engineer specifies the column, its connections and its footing.
Steel column requirements
Subsection 9.17.3. has four short rules for steel columns:
| Rule | Requirement | Article |
|---|---|---|
| Pipe size | Outside diameter at least 73 mm, wall at least 4.76 mm, unless capacity is shown to be adequate for another size | 9.17.3.1. |
| End plates | At least 100 × 100 × 6.35 mm at each end; full beam width under a wood beam | 9.17.3.2. |
| Top plate exception | Not needed on a steel beam where the column is attached to the beam another way | 9.17.3.2.(2) |
| Paint | Exterior steel columns susceptible to corrosion get at least one coat of rust-inhibitive paint | 9.17.3.3. |
| Adjustable columns | Conform to CAN/CGSB-7.2 where the imposed load is 36 kN or less; otherwise design under Part 4 | 9.17.3.4. |
For reference, 73 mm is about 2-7/8 in, 4.76 mm is 3/16 in and 6.35 mm is 1/4 in.
Two points are worth drawing out:
- HSS posts are allowed. Sentence 9.17.3.1.(2) permits sizes other than the minimum pipe where the loadbearing capacity is shown to be adequate. Square and rectangular HSS posts are common on engineered drawings for that reason. See our HSS sizes chart for the metric sections.
- Teleposts have a load ceiling. The code's explanatory note warns that with Part 9 floor loads and spans, the load on a column can exceed the 36 kN that CAN/CGSB-7.2 covers. Our article on whether teleposts can be permanent covers the label, the load and when to switch to a fixed post.
Wood, masonry and concrete columns
Not every basement column is steel. The code sets minimums for the other materials too:
| Column type | Minimum size | Other requirements |
|---|---|---|
| Wood, rectangular | 140 mm × 140 mm, and not narrower than the supported member | Solid, glued-laminated or built-up |
| Wood, round | 184 mm diameter, and not narrower than the supported member | Separated from concrete in contact with the ground by 0.05 mm polyethylene or Type S roll roofing |
| Unit masonry | 290 mm × 290 mm or 240 mm × 380 mm | Concrete block to CSA A165.1 with at least 15 MPa net-area strength |
| Solid concrete | 200 mm × 200 mm rectangular, or 230 mm diameter round | Concrete conforming to Section 9.3. |
Source: 2024 Ontario Building Code, Subsections 9.17.4. to 9.17.6.
Built-up wood columns must use full-length members at least 38 mm thick, either bolted with bolts of at least 9.52 mm diameter at no more than 450 mm on centre, or nailed with nails at least 76 mm long at no more than 300 mm on centre. Smaller wood columns than the minimums are only allowed where calculations show they are adequate, apart from garages and carports, where Article 9.35.4.2. permits 89 mm × 89 mm wood columns.
If you are weighing a wood post against steel, our comparison of lally columns vs wood posts goes through the practical differences.
Footings, fastening and lateral support
These rules apply to every column material:
- Centred on a footing. Article 9.17.2.1. requires columns to be centrally located on a footing conforming to Section 9.15. Table 9.15.3.4. gives minimum column footing areas of 0.40 m² supporting one floor and 0.75 m² supporting two floors, for columns spaced 3 m on centre, and Article 9.15.3.7. adjusts the area in proportion where columns are spaced differently. Our guide to lally column footing requirements covers sizing in detail.
- Fastened to the supported member. Sentence 9.17.2.2.(1) requires columns to be securely fastened to the beam to reduce the chance of the column and beam moving sideways relative to each other.
- Laterally supported. Columns must be laterally supported against racking, either directly or through their connection to the supported members (Sentence 9.17.2.2.(2)). In a basement, a column fastened at the top to a beam and floor system and bearing on a footing at the bottom is the usual arrangement.
A post standing on the basement slab with no footing, or one held at the top by shims and friction, doesn't meet these rules, whatever the post is made of.
How column spacing ties into the rules
The column rules don't set a spacing on their own. Spacing is set by the beam: the distance between columns is the beam span, and the beam has to be sized for it from the span tables or by design. Wider spacing also means more load on each column and a bigger footing, which can push a telepost past its 36 kN limit. Our article on how far apart basement columns should be works through that relationship.
Replacing, moving or removing a basement column
Owners usually start asking about the code when they want to finish a basement, open up a room or replace a rusty post. A few things to know before any work starts:
- Moving or removing a column is a structural alteration. It changes the beam span and the load on the remaining columns and footings, and in GTA municipalities it normally needs a building permit and drawings from a qualified designer or engineer.
- Swapping like for like still needs care. The beam has to be temporarily supported before the old column comes out, and the new one must be cut to fit exactly and fastened to the beam.
- Check what is under the slab. Older houses sometimes have posts on small or no footings. A new column load on an inadequate footing is a common reason for cracked slabs and sagging floors.
- Don't jack a sagging beam with a telepost. Lifting a structure moves loads into places they weren't designed for and can crack walls, finishes and foundations.
Steel posts and plates made to your drawings
We fabricate HSS and steel posts for basements with base and cap plates welded on, along with the beams and plates they connect to, and we supply and install basement beams and posts. Send us your drawings or measurements for a quote, or see our steel products for what we make.
Frequently asked questions
What size steel column is required in a basement in Ontario?
Under Article 9.17.3.1. of the 2024 Ontario Building Code, a steel pipe column needs an outside diameter of at least 73 mm and a wall thickness of at least 4.76 mm. Other sizes, including square or rectangular HSS, are allowed where their loadbearing capacity is shown to be adequate.
Does a basement steel post need plates at the top and bottom?
Yes. Steel columns need steel plates at least 100 mm by 100 mm by 6.35 mm thick at each end, and under a wood beam the top plate must extend across the full width of the beam. The top plate can be omitted on a steel beam where the column is attached to the beam another way.
Can a basement column sit on the concrete floor slab?
No. Article 9.17.2.1. requires columns to be centred on a footing that conforms to Section 9.15. A basement floor slab is not a footing, so a column needs a proper pad footing under it.
What is the minimum wood post size for a basement in Ontario?
Wood columns must be at least as wide as the beam they support and not less than 140 mm by 140 mm for rectangular columns or 184 mm diameter for round columns, unless calculations show a smaller size is adequate.
Is a lally column the same as a telepost?
Not exactly. Lally column is a US name for a steel pipe column. In Canada, adjustable steel columns are called teleposts and must conform to CAN/CGSB-7.2 when used under Part 9 with loads up to 36 kN.
