A steel lintel is a beam placed over an opening in a masonry wall, carrying the brick above the door or window so the opening stays square. In most houses it is a single galvanized steel angle, tucked under the brickwork where you only ever see its bottom leg.
That simplicity is deceptive. The Brick Industry Association is blunt about it: lintels are “too critical an element to be left to rule-of-thumb designs,” and most of the cracks that appear above openings in masonry walls come from lintels that deflected more than they should have.
What a Steel Lintel Actually Carries
Not all the wall above it. Mortared masonry behaves like a very shallow arch: once it has cured, brickwork above an opening tends to span across the gap on its own, and only a wedge of masonry near the opening ends up resting on the lintel. That is called arching action.
Technical Notes 31B treats that wedge as a triangle and gives the resulting maximum moment as M = WL/6, where W is the total load on the lintel and L is the span measured center to center of the end bearings. Designers who prefer a uniform load can take two thirds of the triangle height times the unit weight of the masonry and use the familiar wL²/8 instead.
There is an important exception. Arching action is not assumed when a concentrated load lands near the opening, such as a floor beam or a roof truss bearing just above the head. In that case the lintel has to carry the point load spread over a length, with no help from the arch.
Types of Steel Lintel
Loose Angle Lintels
The common case. A single steel angle is laid in the wall across the opening, with the horizontal leg supporting the brick and the vertical leg hidden in the collar joint or cavity. These suit brick veneer and cavity wall construction, where only one wythe of masonry sits above the opening.
Combination Lintels
In solid masonry walls a single loose angle usually cannot do the job, so two or more shapes are combined: a pair of angles back to back, an angle welded to a plate, or an angle bolted to a wide flange section. The wide flange carries the bending while the angle gives the brick something to sit on. If you are picking the structural half of that pair, our wide flange beam sizes chart lists every W shape with its section properties.
Shelf Angles
On multi-story buildings a continuous angle is bolted back to the structural frame at each floor, carrying a full story of veneer rather than one opening. It is a relief angle first and a lintel second, and it usually needs a proper connection design rather than simple bearing.
Minimum Requirements
These come from the Brick Industry Association’s Technical Notes 31B on structural steel lintels (checked September 2026):
| Item | Minimum |
|---|---|
| Steel grade | ASTM A36 or better |
| Angle thickness | 1/4 in (6 mm) |
| Horizontal leg, nominal 4 in (100 mm) brick | 3 1/2 in (90 mm) |
| Horizontal leg, nominal 3 in (75 mm) brick | 3 in (75 mm) |
| Harsh climates and exposures | Galvanized steel recommended |
The leg width rule has a simple logic behind it: the horizontal leg has to be wide enough to support the brick above it without leaving the outer face unsupported. A 3 in leg under a nominal 4 in brick leaves too much of the unit hanging.
Common Lintel Angle Sizes
Angles that meet the minimums above, with real dimensions and properties from the AISC Shapes Database v16.0. Sx is the elastic section modulus about the strong axis, which is what bending capacity scales with.
| Angle | Weight (lb/ft) | Area (in²) | Ix (in⁴) | Sx (in³) |
|---|---|---|---|---|
| L3-1/2×3-1/2×1/4 | 5.8 | 1.70 | 2.00 | 0.787 |
| L4x3-1/2×1/4 | 6.2 | 1.82 | 2.89 | 1.01 |
| L4x4x1/4 | 6.6 | 1.93 | 3.00 | 1.03 |
| L4x4x5/16 | 8.2 | 2.40 | 3.67 | 1.27 |
| L5x3-1/2×5/16 | 8.7 | 2.56 | 6.58 | 1.92 |
| L6x4x5/16 | 10.3 | 3.03 | 11.4 | 2.77 |
| L6x4x3/8 | 12.3 | 3.61 | 13.4 | 3.30 |
Notice how much faster stiffness grows than weight. Going from the L4x4x1/4 to the L6x4x5/16 adds 56 percent to the weight per foot but nearly quadruples Ix, because the extra material went into depth rather than thickness. That is the same principle that governs every rolled section, and it is worth understanding before you pick anything: see how to read steel beam sizes for what each figure in a shape designation means.
To work out what a run of angle will weigh for delivery or lifting, the steel beam weight calculator handles any length once you know the pounds per foot.
Deflection Is the Usual Failure
Lintels rarely break. They sag, and the masonry above them cracks because brickwork has almost no tolerance for movement. This is why the allowable load tables in Technical Notes 31B cap deflection at L/600, a far tighter limit than the L/360 used for ordinary floor beams. Over a 6 ft opening, L/600 is a tenth of an inch.
Those same tables assume the angle is laterally supported and are based on an allowable bending stress of 22,000 psi. Both assumptions matter. An angle loaded off its shear center wants to twist as well as bend, and the tables explicitly say that angles subject to torsion need a special investigation.
Corrosion and Why Galvanizing Is Worth It
A lintel sits in the wettest part of a wall. Water runs down the cavity, collects on the horizontal leg, and stays there. A painted angle in that position is on a clock.
Hot-dip galvanizing works differently from paint. The American Galvanizers Association describes the coating as providing barrier and cathodic protection plus a zinc patina, and notes that it typically delivers two to five times longer maintenance intervals than paint-only systems (checked September 2026). The cathodic part is what matters at a scratch: bare steel in a paint system rusts from the nick outwards, while zinc corrodes sacrificially and protects the exposed steel next to it.
Replacing a rusted lintel means taking down the masonry above it, so the cost of galvanizing at fabrication is trivial next to the cost of getting it wrong.
Frequently Asked Questions
What size steel lintel do I need for a 6 ft opening?
It cannot be answered from the span alone. The answer depends on how much masonry sits above, whether any beam or truss bears near the opening, the wall thickness, the bearing length available and the deflection limit. This is exactly the rule-of-thumb sizing the Brick Industry Association warns against. A licensed structural engineer has to size it.
How much should a steel lintel bear on each side?
Enough that the masonry under each end is not overstressed. The required bearing area is calculated from the end reaction and the allowable compressive stress of the supporting masonry, which varies with the wall type and mortar. It is a calculation, not a fixed number.
Can I use an I-beam as a lintel instead of an angle?
Yes, and for wide or heavily loaded openings it is common. A wide flange section carries far more than an angle of similar weight, but it gives the outer brick nothing to sit on, so it is usually paired with an angle or a plate. See types of steel beams for how the shape families differ.
What is the difference between a lintel and a header?
They do the same job in different materials. Lintel is the term used over masonry openings and usually means steel, precast concrete or reinforced brick. Header is the wood framing term for the member over a door or window in a stud wall.
Do steel lintels need a damp-proof course above them?
Cavity walls normally need flashing and weep holes above the lintel so that water reaching the cavity is directed back out rather than sitting on the steel. The detailing varies by wall type and climate, and it is part of the wall design rather than the lintel selection.
The Short Version
Use A36 steel or better, at least 1/4 in thick, with a horizontal leg of 3 1/2 in under nominal 4 in brick. Galvanize it. Expect deflection rather than strength to govern, and remember that arching action disappears the moment a concentrated load lands near the opening. Then have the size confirmed by a licensed structural engineer, because a lintel is one of the few members where the failure shows up as cracks across someone’s front elevation.
Reference information only, not engineering advice. Disclaimer.