There is no single required spacing for basement columns: the distance between columns is the span of the beam they support, so the beam decides it. Under the 2024 Ontario Building Code, a typical built-up wood beam (three 2x10s) carrying one floor can span about 3 m, while a W200x27 steel beam in the same position can span 6.3 m. Wider spacing also means more load on each column and a bigger footing under it.
That's why two houses of the same size can have very different basements: one with a post every 2.5 m, the other with one post in the middle. Here's how the numbers fit together.
Column spacing is beam span
Columns hold up a beam, and the beam holds up the floor joists. The span tables in Part 9 of the code give the maximum distance a beam may span between supports for a given size, so the column spacing can't exceed that. The inputs are:
- The beam: material, size and grade
- Supported joist length: half the sum of the joist spans on both sides of the beam. Joists of 4.0 m on one side and 4.4 m on the other give 4.2 m.
- Number of floors carried: a beam under a bungalow carries one floor, a beam under a two-storey centre wall carries two
- Floor use: the tables assume residential floor loads, and concrete topping or heavy finishes reduce allowable spans
The code's tables also stop at certain limits. The column rules in Section 9.17. only cover beams carrying up to 2 wood-frame floors with supported joist lengths up to 5 m, and anything beyond that is designed under Part 4. Our guide to basement column rules in the Ontario Building Code covers that scope.
Column spacing under built-up wood beams
Spans for built-up wood floor beams come from Tables 9.23.4.2.-H to 9.23.4.2.-K. For a common case, spruce-pine-fir No. 1 or No. 2 supporting one floor, Table 9.23.4.2.-H gives these maximum clear spans in metres:
| Supported joist length | 3-ply 38 × 184 (2x8) | 3-ply 38 × 235 (2x10) | 4-ply 38 × 235 (2x10) | 3-ply 38 × 286 (2x12) |
|---|---|---|---|---|
| 3.0 m | 2.85 | 3.52 | 4.01 | 4.09 |
| 3.6 m | 2.63 | 3.22 | 3.71 | 3.73 |
| 4.2 m | 2.44 | 2.98 | 3.44 | 3.46 |
| 4.8 m | 2.28 | 2.79 | 3.22 | 3.23 |
Source: 2024 Ontario Building Code, Division B, Table 9.23.4.2.-H. Spans are clear spans between supports; add the bearing length at each end for the total beam length.
Carrying two floors (Table 9.23.4.2.-I), the same 3-ply 2x10 beam at a 4.2 m supported length drops from 2.98 m to 2.23 m. So a post every 2.4 to 3 m (8 to 10 ft) is roughly what the tables give for a one-storey house with a 2x10 beam, and too far apart for a two-storey house with the same beam.
The notes to these tables also require reduced spans (multiply by 0.8) where the floors have a concrete topping up to 51 mm, and minimum bearing lengths at the ends of the beam.
Column spacing under steel beams
Steel beams span much further for the same depth, which is why they're used to open up basements. Table 9.23.4.3. gives maximum spans for steel beams supporting floors in dwelling units. At a 4.2 m supported joist length:
| Section | One storey supported | Two storeys supported |
|---|---|---|
| W150x22 | 4.8 m | 3.8 m |
| W200x27 | 6.3 m | 5.3 m |
| W250x33 | 8.0 m | 6.5 m |
| W310x39 | 9.8 m | 7.9 m |
Source: 2024 Ontario Building Code, Division B, Table 9.23.4.3.
So with a W200x27 under a bungalow, columns could be 6.3 m apart instead of about 3 m with a 3-ply 2x10. The trade-off is depth and load: a deeper beam can cost headroom, and each column now carries roughly twice the floor area. The full tables, their assumptions and the lateral support conditions are in our steel beam span tables guide.
Wider spacing means more load on each column
The code's explanatory note to Article 9.17.3.4. describes how Part 9 estimates column load: the supported area times the floor live load, where the supported area is half the joist span on each side of the beam multiplied by half the beam span on each side of the column. The residential live load in the code is 1.9 kPa.
Worked through for an interior column with a 4.2 m supported joist length:
| Column spacing | Floors carried | Supported area | Estimated live load on column |
|---|---|---|---|
| 3.0 m | 1 | 12.6 m² | about 24 kN |
| 3.0 m | 2 | 12.6 m² per floor | about 48 kN |
| 6.3 m | 1 | 26.5 m² | about 50 kN |
That matters because an adjustable steel column (telepost) to CAN/CGSB-7.2 is only accepted under Part 9 for loads up to 36 kN. At wider spacings, or with two floors above, the column usually needs to be a fixed steel post selected or designed for the load. Our article on whether teleposts can be permanent explains the label and the limit. This is a simplified live load check from the code's note; your designer works out the real loads, including dead load where Part 4 design applies.
Wider spacing means bigger footings
Every column must sit centred on a footing that conforms to Section 9.15. Table 9.15.3.4. sets the minimum footing area for columns spaced 3 m on centre:
| Floors supported | Minimum column footing area |
|---|---|
| 1 | 0.40 m² |
| 2 | 0.75 m² |
| 3 | 1.0 m² |
Article 9.15.3.7. requires the footing area to be adjusted in proportion to the distance between columns. Move from 3 m to 6 m spacing and a one-floor column footing goes from 0.40 m² to about 0.80 m². These footing rules also only apply where supported joist spans don't exceed 4.9 m; beyond that, footings are designed. Our guide to lally column footing requirements covers footing sizes and thickness.
When posts are removed to open up a basement, the remaining posts usually need new, larger footings. That's often the bigger part of the job than the beam itself.
How many columns do you need?
A simple way to estimate:
- Measure the beam line between its end supports (usually the foundation walls).
- Find the maximum span for your beam, floors and supported joist length.
- Divide the length by the maximum span and round up. That's the number of spans.
- Subtract one. That's the number of columns.
Example: a 12 m beam line under a one-storey house with a 4.2 m supported joist length.
- 3-ply 2x10 SPF beam, 2.98 m maximum span: 12 ÷ 2.98 = 4.03, so 5 spans and 4 columns.
- W200x27 steel beam, 6.3 m maximum span: 12 ÷ 6.3 = 1.9, so 2 spans and 1 column.
In practice, columns also get placed where they suit the layout: inside a future wall, clear of a doorway or stair, or away from ductwork. Spans can always be shorter than the maximum, never longer.
Changing your column layout
Removing or moving a basement column changes the beam span, the load on the other columns and the footings, so it's a structural change. Expect to need:
- A designer or engineer to size the new beam, columns and footings, especially where spans go beyond the Part 9 tables
- A building permit in GTA municipalities
- Temporary shoring while the old posts come out and the new beam goes in
Our guide to the cost to install a steel beam in a basement walks through how these jobs are put together.
Beams and posts made to your layout
We supply and install basement beams and posts, and fabricate steel beams with cap plates and holes, along with HSS posts with base and cap plates welded on. Send us your drawings or beam schedule for a quote, or see our steel products.
Frequently asked questions
How far apart can steel columns be in a basement?
As far apart as the beam can span. In Table 9.23.4.3 of the 2024 Ontario Building Code, a W200x27 steel beam carrying one storey with a 4.2 m supported joist length can span 6.3 m, so columns could be up to 6.3 m apart. Built-up wood beams usually need columns much closer together.
What is the typical spacing for basement columns under a wood beam?
It depends on the beam and the floor it carries. For a 3-ply 38 x 235 mm (2x10) spruce-pine-fir No. 1 or No. 2 beam supporting one floor with a 4.2 m supported joist length, Table 9.23.4.2.-H allows a clear span of 2.98 m. Carrying two floors, the same beam drops to 2.23 m.
How many lally columns do I need?
Divide the beam's length between end supports by the maximum span allowed for that beam, round up to get the number of spans, and subtract one. A 12 m beam line with a 2.98 m maximum span needs 5 spans and 4 columns. A beam that spans 6.3 m needs 2 spans and 1 column.
Does wider column spacing need bigger footings?
Yes. Table 9.15.3.4 gives column footing areas for columns spaced 3 m on centre, 0.40 m2 for one floor and 0.75 m2 for two, and Article 9.15.3.7 requires the area to be adjusted in proportion for other spacings. Double the spacing roughly doubles the footing area.
