Steel Lintels for Concrete Block (CMU) Walls

In a concrete block (CMU) wall, a steel lintel is usually a pair of steel angles, one under each face of the block, or a steel beam with a plate welded to its bottom flange so it carries the full width of the wall. Each end needs at least 150 mm of even, level bearing on masonry, concrete or steel, and with hollow block that normally means filled cores or solid units under the bearings. Ontario's code has a table for angle lintels in masonry walls, but many block wall openings, especially wide ones or ones under floor loads, are sized by a designer or engineer.

This post covers block walls above and below grade in houses, garages and small commercial buildings. For brick veneer over wood framing, see steel lintel sizes under the Ontario Building Code.

Why block walls need a different lintel

A brick veneer wall is a single 90 to 100 mm wythe sitting on one angle. A block wall is different:

• It's wider. Standard metric concrete block is 190 mm wide for a 200 mm wall, and thicker units are used for taller or more heavily loaded walls. One angle under one face doesn't support the other face.
• It's hollow. The block is two thin face shells joined by webs. Load bearing on the end of a lintel goes into those shells unless the cores below are filled.
• It's often loadbearing. Block walls in garages, additions and commercial buildings commonly carry floor joists, roof framing or a bond beam. The lintel carries the wall above plus whatever the wall supports.
• It may be reinforced. Reinforced block walls have vertical bars in grouted cores and horizontal reinforcement or bond beams. The lintel has to work with that layout, not cut through it.

Lintel options for block walls

Double angle lintels

The most common steel solution in a block wall is two angles, back to back, each carrying one face of the wall. The angles are chosen so their legs suit the block coursing and the wall width.

The notes to Table 9.20.5.2.-A in the 2024 Ontario Building Code say that interior and exterior angles in 200 mm walls, and interior angles in 300 mm walls, are bolted together when the clear span is over 1,800 mm. Bolting makes the pair act together instead of each angle twisting on its own.

Steel beams with a bottom plate

For wider openings, or where the wall carries a floor or roof, a single angle pair may not have the strength or stiffness. A common answer is a steel beam (often a W-section or rectangular HSS) with a steel plate welded to the bottom, wide enough to support the full thickness of the block. The beam carries the load and the plate gives the block something to sit on. The size of the beam, plate and welds is set by the designer.

Non-steel options

Reinforced masonry lintels, built from lintel or bond beam units with reinforcing bars and grout, are common in new reinforced block walls because they match the wall and need no separate steel. Masonry designed under Part 4 of the code follows CSA S304, "Design of masonry structures". If your wall is reinforced, see rebar in concrete block walls for how the bars are laid out.

What the Ontario code tables cover

Article 9.20.5.2. of the 2024 OBC requires masonry over openings to be supported by steel lintels, reinforced concrete lintels or masonry arches designed to carry the loads. For steel angle lintels in masonry walls, Table 9.20.5.2.-A gives sizes based on:

• Clear span, from 1.2 m or less up to 3.0 m
• Wall thickness, 203 mm or 305 mm
• Floor load per metre of span, from no floor load up to 21,900 N/m

The table is organized around solid masonry walls with an exterior angle under a 100 mm brick (or stone) face and interior angles under the backing. At the longest spans and heaviest floor loads there is no entry, which means the lintel must be designed. The notes also let you omit the floor load when the distance from the top of the opening to the floor construction above is greater than the width of the opening, and state that the table assumes deflection limited to 1/700 of the span.

For a plain single-wythe block wall, a block-backed wall with a different face, or any wall with concentrated loads such as a beam or girder truss bearing above the opening, the table doesn't map neatly and the lintel is normally designed. The full table and how to read it are in our steel lintel sizes guide.

Bearing on concrete block

Steel lintels in the code tables need even and level bearing of at least 150 mm at each end, on masonry, concrete or steel (Sentence 9.20.5.2.(3.1)). In a block wall, a few more points come into play:

• Fill the cores under the bearing. Designers commonly call for the block cores below each lintel end to be grouted, or for solid units to be used, so the lintel bears on solid masonry instead of two thin face shells. Larger loads may need a grouted column of cores several courses deep.
• Longer bearing for heavier lintels. 150 mm is a minimum for table lintels. Beams with plates and designed lintels often need more, which the designer will show.
• Keep it level. The bearing surface should be true, with the lintel bedded in mortar or on a levelling course as detailed, not propped on shims.
• Coordinate with reinforcement. In reinforced walls, vertical bars at the jambs and the bond beam above are part of the design.

New openings in existing block walls

Cutting a new door, window or garage opening into an existing block wall is common on renovations and commercial fit-outs. It's also a structural alteration. In outline, the process usually involves:

1. Design. A designer or engineer checks what the wall carries, sizes the lintel and specifies the bearing, including whether cores below the bearings need to be filled.
2. Permit. A loadbearing wall alteration normally needs a building permit in GTA municipalities.
3. Temporary support. The wall above is shored, often with needles through the wall and posts on each side, before any block is removed.
4. Cutting and setting. The opening is cut, bearings are prepared and the lintel is set and packed tight to the masonry above.
5. Making good. Shoring comes out only once the lintel is carrying the load as designed.

Block foundation walls add soil pressure and often carry beams and posts, which is why basement openings are almost always engineered. See steel lintels for basement egress windows for that case, and installing a steel lintel in an existing brick wall for a step-by-step view of a masonry lintel retrofit.

Corrosion and finish

Lintels in exterior block walls get wet, especially in single-wythe walls without a cavity. The code requires steel angle lintels supporting masonry to be prime painted or otherwise protected from corrosion (Sentence 9.20.5.2.(4)). For exterior block walls, garage door heads and anything near grade, galvanizing is worth considering. Our article do steel lintels rust covers finishes and flashing.

Lintels made for your block wall

We supply angle lintels cut to length, punched or welded as needed, and fabricate lintels and beams with welded plates to your drawings. Send us the opening width, wall thickness and your designer's details and we'll quote your lintels. See our steel products for the full range.