A steel angle lintel is designed by working out the masonry load it actually carries (usually a 45-degree triangle of brick, thanks to arching), checking the angle's bending resistance with factored loads to CSA S16, and then checking deflection, which almost always governs. The Ontario Building Code's own lintel tables were built on a mid-span deflection limit of span/700. In the worked example below, a 3.0 m opening in 90 mm brick veneer needs an L127x89x7.9, which matches the code table.
The example shows how the numbers come together. It isn't a substitute for a designer when your opening is outside the code tables.
When a lintel needs designing
For houses and small buildings, Article 9.20.5.2 of the 2024 OBC gives prescriptive lintel sizes, so many openings never need a calculation. Our steel lintel sizes guide walks through those tables.
A lintel has to be designed when:
- The opening is wider than the largest span in the table for your wall.
- A floor, roof, beam or post bears on the masonry above the opening.
- There isn't enough solid masonry above the opening for arching to work, or there's another opening close above.
- It's a new opening cut into an existing loadbearing wall.
- The building is outside Part 9, where lintels are engineered under Part 4 (steel to CSA S16, masonry to CSA S304).
Design assumptions from the Ontario code
The Ontario code's explanatory notes publish the assumptions behind its lintel tables. They're a sensible, documented starting point for a hand check:
| Assumption | Value used in the OBC notes |
|---|---|
| Brick density | 18.9 kN/m³ |
| Weight of 89 mm brick veneer | 0.089 m x 18.9 = 1.68 kPa of wall |
| Weight of 100 mm stone veneer | 2.26 kPa |
| Arching | Brick outside the 45-degree triangle above the opening is not counted |
| Deflection limit | Span/700 at mid-span |
| Steel yield strength | 300 MPa |
Arching is the key idea. Bonded masonry above an opening spans across it like an arch, so the lintel only carries the triangle of brick under that arch. With 45-degree sides, the triangle's height is half the span. Arching relies on solid masonry above and beside the opening. If a window, a floor bearing, or the top of the wall cuts into that zone, the assumption doesn't hold and the full load has to be considered.
Worked example: 3.0 m opening in brick veneer
Given: a 3.0 m clear opening in 90 mm brick veneer on a wood-frame house. No floor or roof bears on the veneer, and there's plenty of solid brick above. The angle has 150 mm of bearing at each end.
Step 1: Design span
Use the distance between the centres of bearing: 3.0 m + 0.075 m + 0.075 m = L = 3.15 m.
Step 2: Loads
- Triangle of brick: height L/2 = 1.575 m, area = L²/4 = 2.48 m².
- Brick load: 2.48 m² x 1.68 kPa = 4.17 kN (total, triangular distribution).
- Self-weight of a trial L127x89x7.9: about 12.9 kg/m, or 0.13 kN/m, which is 0.40 kN over the span.
Step 3: Bending
For a triangular load with total W, the mid-span moment is W x L / 6. For the uniform self-weight it's w x L² / 8.
- Brick: 4.17 x 3.15 / 6 = 2.19 kN·m
- Self-weight: 0.13 x 3.15² / 8 = 0.16 kN·m
- Specified moment: 2.35 kN·m
- Factored with the dead load factor of 1.4 (OBC Table 4.1.3.2.-A): Mf = 3.28 kN·m
The angle stands with its 127 mm leg vertical. Its elastic section modulus to the top of that leg is about 31.5 x 10³ mm³. A simple elastic resistance, using φ = 0.90 and Fy = 300 MPa:
Mr = 0.90 x 31,500 x 300 = 8.5 kN·m, comfortably above 3.28 kN·m.
A full CSA S16 check also covers how a single angle bends and twists. Angles bend about inclined principal axes and can buckle sideways unless restrained, which brick ties and the masonry itself usually provide. That's a designer's judgment, and one reason long lintels get engineered.
Step 4: Deflection
Deflection uses unfactored loads. With E = 200,000 MPa and I = 2.74 x 10⁶ mm⁴ about the horizontal axis:
- Triangular brick load: W x L³ / (60 x E x I) = 3.96 mm
- Self-weight: 5 x w x L⁴ / (384 x E x I) = 0.30 mm
- Total: 4.26 mm
- Limit: 3,150 / 700 = 4.50 mm
The angle passes, at about 95% of the limit. Strength used less than 40% of capacity, so deflection governs, which is typical for lintels.
Step 5: Compare the alternatives
| Angle | Mass (kg/m) | I (10⁶ mm⁴) | Deflection | Limit | Result |
|---|---|---|---|---|---|
| L102x89x7.9 | 11.4 | 1.47 | 7.9 mm | 4.5 mm | Fails |
| L127x89x6.4 | 10.4 | 2.23 | 5.2 mm | 4.5 mm | Fails |
| L127x89x7.9 | 12.9 | 2.74 | 4.3 mm | 4.5 mm | Passes |
Section properties are from the AISC Shapes Database (metric) for the equivalent imperial angles.
Sanity check: OBC Table 9.20.5.2.-B allows an L127x89x7.9 up to 3.31 m in 90 mm brick, and the next lighter angle in the table, L102x89x6.4, only to 2.66 m. Our hand check lands in the same place.
Things the calculation doesn't show
- Bearing. Lintels sized from the Ontario tables need at least 150 mm of even, level bearing at each end. Engineered lintels also check the bearing stress on the masonry below. More in steel lintel bearing length.
- Rotation. The veneer sits on the horizontal leg, off to one side of the vertical leg, so the load tries to roll the angle. Short spans cope easily; long or heavily loaded ones may need a different detail.
- Floor and roof loads. When the lintel also carries joists, rafters or a girder truss, it's no longer a veneer lintel. The load can be several times larger, and a W-beam with a welded plate is often the answer. The OBC's Table 9.20.5.2.-C covers some of those cases. See steel lintel vs beam.
- Corrosion. Steel angle lintels supporting masonry must be prime painted or otherwise protected (Article 9.20.5.2). Flashing over the lintel keeps water off it.
- Orientation. The long leg goes vertical. Install an L127x89 with the 89 mm leg vertical and its stiffness drops to well under half.
About lintel load calculators
Online "steel lintel load calculators" can be useful for a first look, but check what they assume. Many are built for US or UK practice, use imperial angles or different deflection limits, and assume arching without asking whether the wall above supports it. In Ontario, start with the OBC tables for Part 9 openings and use a designer for anything outside them.
Getting lintels made
We supply steel angle lintels cut to length and punched or welded as needed, along with beams and plates for openings that need more. Send the opening sizes, wall type and any engineer's lintel schedule, and tell us the finish you need. Fitting a lintel into an existing wall? Read how a steel lintel is installed in an existing brick wall first.
Send your opening sizes or drawings for a quote. Need the lintel designed as well? Engineering services are available; see our services.
Frequently asked questions
How do you calculate the load on a steel lintel?
For brick veneer with enough solid masonry above, designers commonly assume arching: the lintel carries only the triangle of brick between 45-degree lines rising from each end of the opening, plus its own weight. Any floor, roof or point load that lands in that zone is added on top.
What deflection limit is used for steel lintels?
The Ontario Building Code's lintel tables are based on a mid-span deflection of span/700 under the brick load. Engineered lintels use the limit set by the designer, often similar, because masonry cracks if its support sags.
Do I need an engineer to design a steel lintel?
For a Part 9 house opening that fits the Ontario Building Code lintel tables, the table sets the minimum angle. Wider openings, floor or roof loads, point loads, openings in existing loadbearing walls and buildings outside Part 9 need a designed lintel.
Which way does an unequal angle lintel go?
The longer leg stands vertical and the shorter leg sits horizontal under the masonry. The vertical leg provides most of the stiffness, so turning the angle the wrong way can cut its stiffness by more than half.
