Steel beams are used to carry load across an open span and deliver it to columns, walls or foundations. In buildings they hold up floors and roofs, carry walls over openings, support mezzanines, cranes and equipment, and pick up columns over open spaces. In houses they're the main basement beam, the beam that replaces a load-bearing wall, wide garage door headers and ridge beams. They're chosen when a span, a load or a tight depth limit is too much for wood or LVL.
This guide runs through the main uses of steel beams in homes and in commercial and industrial buildings, explains why the I-shape is used, and covers when steel is the right call.
Why steel beams are I-shaped
Almost every structural steel beam you'll see is an I-shape, usually a wide-flange (W) beam. The reason is efficiency.
When a beam bends, its top is squeezed and its bottom is stretched, while the middle does little. The I-shape puts most of the steel in the flanges, top and bottom, where it does the most work, and uses a thin web to hold them apart and carry shear. Depth is what makes a beam stiff: in the CISC tables, a W250x33 is slightly stiffer than a W200x46 while weighing about 29% less, simply because it's deeper.
There's a family of I-shaped sections (W, S, HP and M), and they're not interchangeable. Our post on I-beam vs W-beam vs H-beam sorts out the names. Other shapes also work as beams: HSS tubes where a clean look or torsional stiffness matters, channels in tight spots, and built-up plate girders for very heavy loads.
Steel beams in homes
In an Ontario house, steel beams usually turn up in a handful of places:
| Where | What the beam does |
|---|---|
| Main basement beam | Carries the floor joists down the middle of the house to posts and foundation walls |
| Load-bearing wall removal | Replaces a wall so two rooms can open up, often flush with the ceiling |
| Garage door header | Carries the wall and floor or roof above a wide garage door |
| Ridge beam | Supports the roof at the peak so a ceiling can be vaulted without ties |
| Additions and rear wall openings | Carries the wall and floors above large patio doors or wall openings |
| Lintels | Angles or beams over windows and doors in brick or block walls |
| Decks and porches | Long-span beams on steel posts where wood would be too deep |
| Bowing foundation walls | Vertical beams braced against the floor framing to restrain a wall |
The common thread is span, load and depth. A steel beam can carry the same load as a wood or LVL beam in a shallower depth, or span farther at the same depth, which is why it wins when headroom is tight or the opening is wide. Our post on when a house needs a steel beam covers the signs in detail.
In a house, a steel beam usually works alongside wood framing. It's fitted with a wood nailer on top for the joists, or joists are hung from it, and it sits on steel posts or in pockets in the foundation wall.
Steel beams in commercial and industrial buildings
In larger buildings, steel beams are part of a full frame. Their roles:
- Floor beams and girders. Beams carry the floor deck and slab; girders carry the beams to the columns. Together they set the column spacing and floor depth.
- Roof framing. Girders between columns support joists or purlins and the roof deck.
- Transfer beams. Deep beams or plate girders that pick up columns from the floors above so the space below can stay open.
- Lintels and spandrel beams. Beams at the building edge that carry the cladding and brick, and frame window and door openings.
- Mezzanines and platforms. Beam and column frames inside warehouses and plants, carrying storage, offices or equipment. See our steel mezzanine guide.
- Crane and hoist support. Crane runway girders, monorail beams and lifting beams. Our post on sizing an I-beam for a hoist, gantry or monorail covers the extra checks these need.
- Equipment and rooftop unit support. Beams frame openings and carry heavy mechanical units.
- Canopies and entrances. Cantilevered or post-supported beams for canopies and covered walkways.
How these pieces fit together into a frame is covered in what is structural steel framing.
Steel beams beyond buildings
The same shapes show up across construction:
- Bridges. Rolled beams for short spans, plate girders for longer ones.
- Retaining walls and shoring. W and HP sections as soldier piles, with lagging between them.
- Foundations. HP sections driven as piles, and steel grillages under heavy equipment.
- Temporary works. Needle beams for shoring during wall removals, spreader beams and lifting frames.
- Trailers, skids and machine bases. Smaller beams and channels as frames.
When a steel beam is the right choice
Steel isn't always the answer. Designers weigh it against the alternatives.
| Choose steel when | Wood or LVL may be enough when |
|---|---|
| The span is long or the load is heavy | The span is moderate and the load is ordinary floor load |
| Headroom is tight and the beam must be shallow or flush | There's room for a deeper beam |
| A post or column lands on the beam | Loads are spread evenly |
| The beam must carry masonry or a wall above a wide opening | The opening is narrow and framed in wood |
| Long-term creep, shrinkage or moisture are concerns | The beam is dry, enclosed and lightly loaded |
Against concrete, steel beams are lighter, faster to erect and easier to modify; concrete may win where fire resistance, mass or the rest of the structure favours it.
Steel beams also bring things to plan for: corrosion protection in damp or exterior locations, fire protection where the building code requires a rating, getting a heavy beam into an existing house, and a proper connection to the wood framing around it.
Who decides, and how the beam is chosen
A steel beam is a structural member, so its size, bearing and supports come from a design, not a rule of thumb. In Ontario, houses designed under Part 9 of the Building Code can use the code's steel beam span tables within their limits; anything beyond those tables, and all commercial work, is designed by an engineer to CSA S16. Removing a load-bearing wall or adding a beam usually needs a building permit.
Once the beam is on the drawings, the fabricator cuts it to length and adds what it needs: bearing plates, holes for bolts, welded nailer studs or clips, and any camber specified.
Steel beams from Procut
We supply and fabricate steel beams to your drawings, from basement beams and posts to commercial framing, with in-house shop drawings, CWB certified welding and delivery across the GTA and Ontario. We provide supply and installation of structural steel, including basement beams and posts, and engineering services are available for projects that need them.
Send your drawings or beam size for a quote, or browse our steel products.
Frequently asked questions
What are steel beams used for in construction?
Steel beams carry loads horizontally across a span and deliver them to columns, walls or foundations. They support floors and roofs, carry walls over openings, pick up columns over open spaces, and support cranes, hoists, mezzanines and equipment.
Why are I-beams used in construction?
The I-shape puts most of the steel in the flanges, as far from the centre of the beam as possible, where it does the most work resisting bending. The thin web holds the flanges apart and carries shear. The result is a beam that is very stiff and strong for its weight.
When are steel beams used in a house?
Usually where wood or LVL would be too deep, too heavy or too long: the main basement beam, beams that replace a removed load-bearing wall, wide garage door headers, ridge beams for vaulted ceilings, large openings in additions and lintels in brick walls. The designer chooses steel when the span, load or headroom calls for it.
What are wide flange beams used for?
Wide flange (W) beams are the standard beam and column shape in North America. Shallow, narrow W-shapes are used as floor and roof beams; deep ones as girders and transfer beams; and square-ish W-shapes, as wide as they are deep, as columns.
