The 2024 Ontario Building Code includes steel beam span tables for houses in Part 9: Table 9.23.4.3 for beams supporting floors, and Tables 9.23.4.3.-A to -J for beams supporting a roof and one floor. They give the maximum span for common W-shape beams based on the supported joist length and the number of storeys. For example, a W200x27 carrying one storey with a 3.6 m supported joist length can span up to 6.6 m.
These tables are useful for understanding what's typical and for checking a proposal. They're also narrower than most people assume, so read the conditions before relying on one.
What the Part 9 steel beam tables cover
Article 9.23.4.3 of the 2024 OBC (O. Reg. 163/24, Division B) says the spans for steel beams with laterally supported top flanges shall conform to Table 9.23.4.3 for floors, and Tables 9.23.4.3.-A to -J for roofs and floors. The beams must at least meet Grade 350W steel in CSA G40.21.
The code's explanatory note for Table 9.23.4.3 lists its design assumptions:
- Simply supported spans
- Laterally supported top flange
- Yield strength 350 MPa
- Deflection limit of span/360
- Live load 1.9 kPa and dead load 1.5 kPa, with a live load reduction factor for Part 9 buildings
The table is titled for steel beams supporting floors in dwelling units. It assumes the load arrives as uniform floor load through joists sitting on the beam, not as concentrated loads from posts or walls above.
Table 9.23.4.3: maximum spans for steel floor beams
Values are maximum spans in metres. The column headings are the supported joist length, which is half the sum of the joist spans on both sides of the beam.
One storey supported
| Section | 2.4 m | 3.0 m | 3.6 m | 4.2 m | 4.8 m | 5.4 m | 6.0 m |
|---|---|---|---|---|---|---|---|
| W150x22 | 5.5 | 5.2 | 4.9 | 4.8 | 4.6 | 4.5 | 4.3 |
| W200x21 | 6.5 | 6.2 | 5.9 | 5.7 | 5.4 | 5.1 | 4.9 |
| W200x27 | 7.3 | 6.9 | 6.6 | 6.3 | 6.1 | 5.9 | 5.8 |
| W200x31 | 7.8 | 7.4 | 7.1 | 6.8 | 6.6 | 6.4 | 6.2 |
| W250x24 | 8.1 | 7.6 | 7.3 | 7.0 | 6.6 | 6.2 | 5.9 |
| W250x33 | 9.2 | 8.7 | 8.3 | 8.0 | 7.7 | 7.5 | 7.3 |
| W250x39 | 10.0 | 9.4 | 9.0 | 8.6 | 8.4 | 8.1 | 7.9 |
| W310x31 | 10.4 | 9.8 | 9.4 | 8.9 | 8.4 | 8.0 | 7.6 |
| W310x39 | 11.4 | 10.7 | 10.2 | 9.8 | 9.5 | 9.2 | 9.0 |
Two storeys supported
| Section | 2.4 m | 3.0 m | 3.6 m | 4.2 m | 4.8 m | 5.4 m | 6.0 m |
|---|---|---|---|---|---|---|---|
| W150x22 | 4.9 | 4.4 | 4.1 | 3.8 | 3.5 | 3.4 | 3.2 |
| W200x21 | 5.6 | 5.1 | 4.6 | 4.3 | 4.1 | 3.8 | 3.7 |
| W200x27 | 6.4 | 6.1 | 5.6 | 5.3 | 4.9 | 4.7 | 4.4 |
| W200x31 | 6.9 | 6.5 | 6.2 | 5.8 | 5.4 | 5.1 | 4.9 |
| W250x24 | 6.8 | 6.1 | 5.6 | 5.2 | 4.9 | 4.6 | 4.4 |
| W250x33 | 8.2 | 7.7 | 7.0 | 6.5 | 6.1 | 5.8 | 5.5 |
| W250x39 | 8.8 | 8.3 | 7.8 | 7.2 | 6.8 | 6.4 | 6.1 |
| W310x31 | 8.7 | 7.8 | 7.2 | 6.7 | 6.2 | 5.9 | 5.6 |
| W310x39 | 10.0 | 9.3 | 8.5 | 7.9 | 7.4 | 7.0 | 6.7 |
Source: 2024 Ontario Building Code, Division B, Table 9.23.4.3. The section name gives nominal depth in millimetres and mass in kilograms per metre, so a W200x27 is about 200 mm deep and weighs about 27 kg/m. If that naming is new to you, see how to read steel beam sizes.
How to read the table, with a 20 ft example
Step 1: find the supported joist length. Add the joist spans on both sides of the beam and divide by two. Joists spanning 4.0 m on one side and 4.4 m on the other give 4.2 m. The code's note allows straight-line interpolation for lengths between the columns.
Step 2: count storeys supported. One storey means the beam carries one floor. Two storeys means it carries two floors stacked above, such as a main floor and second floor bearing down through a centre wall line.
Step 3: read across. Any section whose value is at least your required span works on paper.
Take the common question of what beam spans 20 feet. Twenty feet is about 6.1 m. With a 4.2 m supported joist length:
- One storey: W200x27 (6.3 m) works, W200x21 (5.7 m) does not. A W250x24 (7.0 m) also works and is lighter per metre, but it's deeper, which costs headroom.
- Two storeys: W200x31 (5.8 m) falls short. W250x33 (6.5 m) and W310x31 (6.7 m) both work.
That's the table answer. Whether it's the right answer for your house depends on everything the table assumes, which your designer checks.
Tables 9.23.4.3.-A to -J: beams carrying a roof and a floor
The second set of tables covers steel beams supporting a roof and one floor in dwelling units where the beam also carries stud walls. They come in pairs by specified roof snow load:
| Snow load | Exterior stud walls with brick veneer | Interior stud walls, or exterior walls with siding |
|---|---|---|
| 1.0 kPa | Table 9.23.4.3.-A | Table 9.23.4.3.-B |
| 1.5 kPa | Table 9.23.4.3.-C | Table 9.23.4.3.-D |
| 2.0 kPa | Table 9.23.4.3.-E | Table 9.23.4.3.-F |
| 2.5 kPa | Table 9.23.4.3.-G | Table 9.23.4.3.-H |
| 3.0 kPa | Table 9.23.4.3.-I | Table 9.23.4.3.-J |
These tables use two inputs: supported roof length and supported floor length, each half the sum of the framing spans on both sides of the beam. They cover more sections, from W150x22 up to W360x57. As an example, Table 9.23.4.3.-A gives a W250x39 a maximum span of 5.04 m with 2.4 m of supported roof and 2.4 m of supported floor.
The design notes for the brick veneer tables assume 300 MPa steel and limit mid-span deflection to span/600 for brick and live load, because brick cracks if its support sags. The siding cases use span/360. The snow load for your location comes from MMAH Supplementary Standard SB-1 (Sentence 9.4.1.1.(3)), so don't guess which table applies.
Lateral support, bearing and posts
The tables only work if the beam is installed the way they assume:
- Lateral support of the top flange. Under Sentence 9.23.4.3.(3), a beam may be considered laterally supported if wood joists bear on its top flange at intervals of 600 mm or less over its full length, the load reaches the beam through the joists, and 19 mm x 38 mm wood strips in contact with the top flange are nailed to the bottom of the joists on both sides. The note says other positive methods of lateral support are acceptable.
- Bearing. Beams need even, level bearing at least 89 mm long at the ends (Article 9.23.8.1).
- Posts and footings. The span is measured between supports, and each support needs a column on a proper footing. See adjustable steel columns for the column rules.
- Exterior beams must be shop primed with rust-inhibitive paint (Article 9.23.8.2).
When the span tables don't apply
Most renovation beams fall outside the tables, which is why they're usually engineered. Common reasons:
- Concentrated loads, such as a post or a bearing wall from the floor above landing on the beam, or a beam supporting another beam.
- Flush beams where the joists frame into the side of the beam on hangers, so the top-flange lateral support detail above doesn't apply as written.
- More than two storeys, heavier floors (tile on concrete topping, for example), or live loads beyond Part 9's limits.
- Cantilevers, openings for stairs, or continuous beams designed to take advantage of continuity.
- Supported joist lengths over 6.0 m, or spans the table doesn't reach.
If any of these apply, the beam is designed under Part 4, and in practice that means a structural engineer. That's also the usual route for removing a bearing wall, covered in our load-bearing wall removal cost guide.
From span table to fabricated beam
Once the section is chosen, the beam still needs a few decisions before it can be made:
- Length: the clear span plus bearing at each end, measured on site.
- Connections: cap plates for the posts, holes for bolting a wood nailer to the top flange, and any end plates or clip angles for steel-to-steel connections.
- Access: a beam that can't fit through the basement stair or window may need to be fabricated in pieces with a designed splice.
See our Canadian W-shape size chart for dimensions of each section.
Send us your beam schedule
Send us your drawings or beam schedule and we'll quote the beams, posts and plates, fabricated with holes and connections and delivered to site. See our steel products for what we make.
Frequently asked questions
What size steel beam can span 20 feet?
It depends on the supported joist length and storeys. In Table 9.23.4.3 of the 2024 OBC, with a 4.2 m supported joist length, a W200x27 reaches 6.3 m (about 20.7 ft) supporting one storey, while two storeys need something like a W250x33 at 6.5 m. Your designer confirms the final size.
Does the Ontario Building Code have steel beam span tables?
Yes. Table 9.23.4.3 covers steel beams supporting floors in dwelling units, and Tables 9.23.4.3.-A to 9.23.4.3.-J cover beams supporting a roof and one floor where the beam carries stud walls with brick veneer or siding.
What does supported joist length mean in the span table?
It is half the sum of the joist spans on both sides of the beam. Joists spanning 4.0 m on one side and 4.4 m on the other give a supported joist length of 4.2 m.
How far can a steel beam span without support?
In Table 9.23.4.3 the longest span is 11.4 m, for a W310x39 carrying one storey with a 2.4 m supported joist length. Real limits depend on loads, depth, lateral support and deflection, so longer or heavier cases are engineered.
What grade of steel do the OBC span tables assume?
Sentence 9.23.4.3.(2) requires beams to at least meet Grade 350W in CSA G40.21. The table's design notes assume a 350 MPa yield strength and a deflection limit of span/360.
