Can a Steel Beam Span 30, 40 or 50 Feet?

Yes, a steel beam can span 30, 40 or 50 feet (about 9.1, 12.2 and 15.2 m), and much further in commercial buildings. The real question is how deep and heavy the beam has to be, and whether a post somewhere in the middle would be the better answer. In Ontario houses, the building code's Part 9 steel beam table tops out at 11.4 m (about 37 ft), so a 30 ft beam can fall inside it for some one-storey cases, while 40 and 50 ft spans have to be engineered.

This guide explains where those spans sit in the code, why long spans get expensive in steel quickly, and what engineers use instead of one big beam.

What the Ontario span tables allow

For houses designed under Part 9 of the 2024 Ontario Building Code, Table 9.23.4.3 lists maximum spans for W-shape steel beams supporting floors, based on the supported joist length (half the sum of the joist spans on both sides of the beam) and whether the beam carries one or two storeys. The table assumes simple spans, a laterally supported top flange, 350 MPa steel and a deflection limit of span/360.

The longest spans in the table come from the two deepest sections listed. Entries at or above 9.1 m (30 ft):

Source: Table 9.23.4.3, 2024 Ontario Building Code (O. Reg. 163/24).

So in a house:

• 30 ft (9.1 m) is possible from the table, but only with the deeper sections and, for most of them, short supported joist lengths. Carrying two storeys, only the W310x39 gets there, and only with short joists.
• 40 ft (12.2 m) is beyond every entry in the table. It's an engineered beam.
• 50 ft (15.2 m) is well beyond it, and in houses usually a sign the layout should be rethought.

Beams carrying a roof and floor with walls above use Tables 9.23.4.3.-A to -J, with their own limits. For how to read all of these, see our guide to steel beam span tables for Ontario homes. For the 7 m to 10 m range, see steel beams for 7 m to 10 m spans.

Why long spans get heavy so fast

Span length hurts a beam in two ways, and both grow faster than the span itself. For a simple beam under a uniform load:

• Bending moment grows with the square of the span. Double the span and the beam has to resist four times the moment.
• Deflection grows with the fourth power of the span. Double the span and, for the same beam and load per metre, it sags sixteen times as much.

The allowable deflection grows too, since limits like span/360 are a fraction of the span. But that only doubles when the span doubles. The net effect is that the beam's stiffness (its moment of inertia) has to rise roughly with the cube of the span to keep the same deflection limit under the same load per metre.

Those ratios are pure arithmetic, but they explain what designers see: going from a 20 ft beam to a 40 ft beam isn't a slightly bigger beam. It's usually a much deeper one, and for floors, stiffness and vibration rather than strength often decide the size.

Depth: the hidden cost of a long span

Steel gets its stiffness from depth. A long-span beam that has to stay stiff will be deep, and depth costs headroom:

• A beam hung below the joists (a drop beam) eats into ceiling height across its whole length.
• A flush beam keeps the ceiling flat but still needs the floor structure to be deep enough to hide it.
• In a basement, a deep beam can conflict with ducts, doors and minimum headroom.

When depth is tight, the designer may use a heavier section of the same depth, two beams side by side, or a different structural system. All of these add steel.

The options engineers compare for 40 and 50 ft

For long spans, a single rolled W-beam isn't the only answer. Depending on the building, an engineer may compare:

• A deep wide-flange beam. Simple to fabricate and connect, but heavy at long spans.
• Open-web steel joists or trusses. Much lighter for the same span, with room for ducts through the web. Common for long-span roofs and floors in commercial work.
• A plate girder. A built-up I-section welded from plate, used where loads or spans exceed what rolled shapes do economically.
• Cambered beams. Long beams are often cambered so they finish level once the dead load is on.
• An intermediate column. Often the cheapest option by far. Halving a 40 ft span to two 20 ft spans cuts the bending in each beam to a quarter. If a post can go somewhere it won't be in the way, it's worth asking about.

Weight, delivery and installation

A long beam also has to be made, moved and set:

• Weight adds up. Mass per metre times length: even a W310x39, one of the two heaviest sections in the Part 9 table, weighs about 476 kg at 12.2 m, and beams that actually span 40 ft under real floor loads are often heavier. See how to calculate structural steel weight.
• Delivery has limits. Very long pieces need suitable trucks and site access for unloading. Our article on standard steel beam lengths and delivery limits covers what to plan for.
• Splices are an option. A beam too long to deliver or place in one piece can sometimes be spliced on site, if the engineer designs the splice.
• Lifting needs planning. Long beams are lifted with equipment, braced until the floor or roof is attached, and set on bearings and posts designed for the reactions at each end.

Don't forget the ends. A long-span beam puts large loads on its supports, so the posts, bearing plates and footings at each end get bigger too. See steel beam bearing length on concrete and masonry.

Who sizes a long-span beam

Any span outside the Part 9 tables, and any beam carrying loads the tables don't cover, needs a design from an engineer working to CSA S16. That includes most 40 and 50 ft beams in houses, garages, shops and commercial buildings. The engineer will want the floor and roof layout, what sits above the beam, the use of the space below, and any limits on depth.

Long-span beams fabricated to your drawings

We supply and fabricate wide-flange beams cut to length with connections, plates and cambering as specified, along with the posts and plates that support them, and deliver across the GTA and Ontario. Shop drawings are prepared in-house and welding is CWB certified. If you don't have an engineer yet, engineering services are available for projects that need them.

Send your drawings for a quote, or see our steel products for beams, posts and plates.