Steel Beams for 7 m to 10 m Spans

A steel beam can span 7 m to 10 m in a house, and for a beam carrying one storey of floor, Table 9.23.4.3 of the 2024 Ontario Building Code puts the answer in the W250 to W310 range: a W250x33 spans 8.0 m at a 4.2 m supported joist length, and a W310x39 spans 9.0 m even at 6.0 m. With two storeys on the beam, most spans past about 8 m fall outside the table and the beam is engineered. Spans this long also change the job around the beam: heavier posts and footings, a beam that weighs several hundred kilograms, and a delivery that needs planning.

This guide gives a span-first lookup from the code table, explains where the table stops, and covers the practical side of long beams. It helps you check a proposal; it is not a design. A beam of this size in an existing house needs a designer or engineer and a building permit.

What changes once you pass 7 m

Under 6 m, a house floor beam is usually a W150 or W200 and two people can carry it. Past 7 m several things change at once:

• Stiffness governs. The code table is built on a deflection limit of span/360 (Note A-Table 9.23.4.3). A 9 m beam may deflect up to 25 mm under full live load and still pass. Longer spans need depth to keep floors from feeling bouncy, which is why the table moves to W250 and W310 sections.
• The beam gets heavy. A W310x39 is 39 kg per metre, so a 9 m length is about 350 kg before plates.
• The posts and footings carry more. Each end support carries roughly half of everything on the beam. Doubling the span between posts roughly doubles the load on each post and footing.
• Delivery and access matter. A 10 m beam needs a suitable truck, a clear route and a plan for getting it into the building.

For spans of 3 m to 6 m, see our metric guide for shorter spans.

Span-first lookup: one storey supported

The table lists the shallowest section in Table 9.23.4.3 whose maximum span meets or exceeds the span on the left, using the lighter section where two have the same depth. "Beyond table" means no section in the code table reaches that span for that case, so the beam must be engineered.

Supported joist length is half the sum of the joist spans on both sides of the beam.

Derived from Table 9.23.4.3, 2024 OBC, Division B.

A single storey of floor is well within reach of steel up to about 9 m. The table's deepest section, the W310x39, covers almost the whole range.

Span-first lookup: two storeys supported

Derived from Table 9.23.4.3, 2024 OBC, Division B. At the shortest supported joist length in the code table (2.4 m), a W310x39 reaches 10.0 m.

With two storeys bearing on it, a beam past 8 m is normally an engineered beam. That does not mean it can't be done in steel; it means the section comes from a structural design, which may call for a deeper or heavier section than any in the table.

How to read it

1. Measure the clear span between supports.
2. Work out the supported joist length. The code allows straight-line interpolation between columns; if you don't interpolate, use the next column to the right.
3. Count storeys supported: the floors whose load reaches the beam, including through bearing walls above it.
4. Check the result against the full table in our OBC steel beam span tables guide.

Worked example: an 8 m open-plan main floor

A two-storey house is being opened up on the main floor. A new beam will carry the second floor over an 8.0 m span between two new posts. Joists run 3.6 m on one side and 4.2 m on the other.

• Supported joist length: (3.6 + 4.2) / 2 = 3.9 m. Use the 4.2 m column to stay conservative.
• Storeys supported: one (the second floor).
• Lookup: W250x33, which the full table allows to exactly 8.0 m at 4.2 m. Interpolating at 3.9 m gives a little more margin.

Now change one thing: the beam is in the basement and a bearing wall on the main floor carries the second floor down onto it. That is two storeys, and at 4.2 m the table gives nothing that reaches 8.0 m. The beam is engineered, or a post is added to break the span.

The beam is a W250x33 at 8 m, so it weighs about 264 kg before plates: not a two-person carry. See how to lift a steel beam into a house without a crane for how beams of this weight are moved in.

When the table does not apply

Table 9.23.4.3 assumes simply supported spans, a laterally supported top flange, Grade 350W steel, the span/360 deflection limit, a 1.9 kPa floor live load and a 1.5 kPa dead load, and load delivered uniformly through joists. Long beams often break one of those assumptions:

• Point loads. A post or bearing wall landing on the beam, very common at these spans, puts it outside the table.
• Roof loads. Roof and floor combinations are covered for some cases by Tables 9.23.4.3.-A to 9.23.4.3.-J; others are engineered.
• Flush beams. Joists hung off the web instead of bearing on the top flange lose the code's lateral support detail.
• Heavy finishes. Tile on concrete topping, heavy partitions, or uses beyond residential loads.
• Garages, shops and commercial floors. These are outside the dwelling-unit table entirely and designed under Part 4.

In any of these cases the engineer sizes the beam and checks the connections, the posts and the footings. For spans well beyond 10 m, see can a steel beam span 30, 40 or 50 feet.

The practical side of a 7 m to 10 m beam

One piece or spliced? A 10 m beam can usually be delivered in one length, but getting it into an existing house may not be possible. Beams can be made in two pieces and bolted together at a splice the engineer designs.

Delivery. Long beams need a truck that can carry them and a clear place to unload. See standard steel beam lengths and delivery limits before you plan the install.

Camber. Long beams are sometimes cambered so they settle close to level under load. The engineer specifies it when it's needed.

Weight at a glance:

Weights are nominal mass per metre times length, before plates and connections.

Adding a post instead. One post at mid-span turns a 9 m span into two 4.5 m spans, which a W150 or W200 can often handle. If a post can stand somewhere without spoiling the room, it is often the simpler job. If not, the long beam is the price of the open space.

Long beams fabricated and delivered

Once the beam is sized, we fabricate it to length with bearing plates, bolt holes for a wood nailer, splices and any connections on the drawings, in a CWB certified shop, and deliver across the GTA and Ontario. We also supply and install structural steel, from basement beams and posts to larger projects, and engineering services are available for projects that need them.

Send your drawings or span details for a quote, or see the steel beams we supply and fabricate.