Steel Beams for Home Additions and Exterior Wall Openings

Opening an exterior wall for a rear addition, a wide patio door or a corner window means replacing the wall's support with an engineered beam, posts at each end and footings under those posts, with temporary shoring holding the house while the work is done. A steel beam is common because it carries heavy loads in a shallow depth, which keeps ceilings flush and openings tall. The cost of the steel depends on the span and the loads above it, but on an addition the beam is usually one line in a much larger budget. This guide covers what makes exterior walls different and what to plan for.

Why exterior walls are different from interior walls

Removing an interior bearing wall is covered in our load-bearing wall removal cost guide. Exterior walls add a few complications:

• They often carry the roof edge. Rafters or trusses bear on the exterior walls, and in a two-storey house so do the second floor's joists and walls.
• They carry the cladding. Brick or stone veneer above an opening needs its own support, separate from the framing.
• They help resist wind. Exterior walls brace the house sideways. Removing a long length of wall, or a corner, can affect that, and the engineer has to account for it.
• They're part of the envelope. The beam and posts sit where insulation, air barrier and flashing have to be continuous, so the detail has to keep water and cold out.
• Older houses may have solid masonry. Many older GTA homes have bearing walls of solid brick rather than wood framing with a brick veneer. Opening one is a different job from opening a veneered stud wall.

Common projects

Rear additions and extensions

When an addition opens into the existing house, part of the old exterior wall comes out. The beam spans the new opening and usually carries the existing roof or upper floor, and sometimes new roof framing from the addition as well. The posts at each end bring the load down to footings, which may be new footings in the addition's foundation or new pads inside the existing basement.

Wide patio doors and window walls

Replacing a standard door with a wide slider or folding door system means a longer opening than the original header was sized for. A steel beam lets the opening stay tall, which matters with tall doors and low ceilings.

Garage openings

Widening a garage door opening in a brick-faced wall involves the same questions about load and veneer. See steel lintels over garage doors for that case.

Corner openings

Removing the corner of a house, for a wraparound window or an open corner to a deck, is the hardest version. The corner is where two walls support each other. Without it, loads from both sides need a new path, which might be two beams meeting at a post set back from the corner, a cantilevered beam, or a rigid frame with moment connections. These are engineered details, and the connections are where the fabrication effort goes.

Brick: veneer or solid masonry

How the brick is supported depends on what kind of wall you have.

Brick veneer on a stud wall. The 2024 Ontario Building Code requires masonry over openings to be supported by steel, reinforced concrete lintels or masonry arches (Article 9.20.5.2). Steel angle lintels supporting veneer follow Table 9.20.5.2.-B, and steel lintels need at least 150 mm of bearing at each end on masonry, concrete or steel. Our steel lintel sizes guide covers those tables.

For wider openings, Sentence 9.20.5.2.(5) and Table 9.20.5.2.-C cover steel beams supporting masonry veneer and a wood stud wall above an opening. Under Sentence (6), those beams must be supported at each end by a steel column and have a plate at least 6 mm thick welded to the flange to carry the veneer. The table assumes the beam supports only the veneer, a stud wall and a limited roof load. If it carries floor loads or larger roof loads, the code points to the steel beam span rules in Article 9.23.4.3, and in practice most renovation beams are engineered.

Solid masonry walls. When the brick itself is the structure, the beam has to carry the masonry above plus whatever bears on it. The engineer will usually detail temporary needles or shoring through the wall, then one or more beams, sometimes paired, with plates and bearing pads at the ends. Installing a lintel or beam in existing brick is covered in how to install a steel lintel in an existing brick wall.

What drives the cost of an extension beam

The steel portion of the price depends on:

• Span and section. Longer spans and heavier loads need deeper or heavier beams, and steel is priced by weight.
• What the beam carries. Roof only, roof plus a floor, a point load from a post above, or a solid brick wall all lead to different sections.
• Plates and connections. Welded veneer plates, end plates, cap plates, bolt holes for wood nailers and beam-to-beam connections at corners.
• Posts. Steel columns at each end with base and cap plates.
• Pieces and splices. If the beam can't be carried in whole, it may be supplied in pieces with a splice designed by the engineer.
• Finish. Shop primer for interior steel; exterior steel needs rust-inhibitive primer at minimum, and exposed steel may need a paint system.

Around the steel, the bigger items are usually engineering, the permit, footings, shoring, demolition, the new envelope details and finishing. Steel isn't the only choice: engineered wood beams work on many openings, and your designer can compare the two on depth, span and connection details.

Permit and process

Opening an exterior bearing wall is a structural alteration, and Ontario municipalities require a building permit for it. Our post on permits for load-bearing wall removal in the GTA explains what GTA cities ask for. On an addition, the opening is part of the addition's permit drawings.

The usual order of work:

1. Design. The designer or engineer sizes the beam, posts and footings and details the connections and veneer support.
2. Permit. Drawings go to the municipality for review.
3. Shop drawings and fabrication. The steel is detailed, cut, drilled and welded to the approved drawings.
4. Footings. New footings under the posts are poured and inspected.
5. Shoring. Temporary supports go in on both sides of the wall.
6. Opening and installation. The wall section is removed, the beam and posts set, and connections made.
7. Inspection, then finishing. Shoring is released only once the new load path is complete.

Don't take a wall down "a bit at a time" without shoring, and don't size a beam by copying a neighbour's job. Each house carries load differently.

Getting steel for your addition

We fabricate wide-flange beams, steel posts, lintels and plates to your engineer's drawings, with CWB certified shop welding and in-house shop drawings, and we supply and install structural steel on residential jobs. Send your permit drawings or engineer's details for a free quote, or contact us to talk through your project. See our steel products for what we make.