Lintels And Openings In Masonry Walls

Cut a hole in a wall and the load that used to travel through that area has to go around it.

The lintel is what carries it across, and it is one of the most frequently undersized elements in residential construction.

What the lintel actually carries

Less than people assume, and in a specific pattern.

Masonry above an opening tends to arch: the brickwork bridges the gap through the interaction of the bricks themselves, and the lintel carries a roughly triangular wedge of load rather than the full height of wall above it.

That arching only works if there is enough masonry above the opening and enough wall either side for the arch to bear on. Which means an opening near the top of a wall, or near a corner, does not get the benefit and the lintel carries considerably more.

On top of that, any concentrated load landing above the opening goes straight into the lintel. A roof beam, a floor joist or a bearer above a window is the case that most often causes trouble, and it is usually not visible from outside.

The types

Galvanised steel angle, the standard for brick veneer and cavity walls. Cheap, quick, and the most commonly used.

Steel beam, a channel or universal section, for wider openings and heavier loads.

Reinforced concrete lintel, precast or cast in place, common in blockwork.

Reinforced masonry, where reinforcement is placed in the cores of blockwork above the opening.

A brick arch, which carries the load by geometry and needs proper abutments either side.

Why they fail

Undersized for the span. Steel angles come in a range of sizes and the wrong one deflects. Deflection is the usual failure mode rather than collapse: the lintel sags, the brickwork above it cannot follow, and a horizontal crack opens along the course above the opening.

Insufficient bearing at the ends. A lintel needs a defined length of masonry bearing each side. Cut short so the brickwork courses work out, it concentrates load on the last brick and crushes it.

A concentrated load not accounted for. The single most common design oversight.

Corrosion. A galvanised angle in a damp cavity, in a coastal suburb, eventually rusts. Rusting steel expands and pushes the brickwork above it up, producing a characteristic horizontal crack with the brickwork lifted. This is very common in older houses and it is effectively the [concrete cancer](/blog/concrete-cancer-in-apartment-buildings) mechanism in a different material.

No damp proofing over the lintel, so water crosses the cavity and shows up inside.

Two openings too close together, leaving a pier between them too narrow to carry the load from both lintels. The pier crushes or the wall cracks vertically.

Widening an existing opening

Common in renovations and it is where the real risk sits.

The wall above has to be supported before anything is removed. That means needles and props, designed and installed, not a brave attempt with a couple of acrow props.

Then the new lintel has to be installed and pinned up tight to the masonry above, so the wall is actually bearing on it before the props come out. A lintel installed with a gap above it does nothing until the wall drops onto it, and that drop is the crack.

Whether the wall is loadbearing changes the difficulty substantially, and establishing that is the first question in [removing a load bearing wall](/blog/removing-a-load-bearing-wall-what-it-takes).

Openings in the wrong place

Some openings are a bigger problem than their size suggests.

Close to a corner, where there is not enough wall for the arch to bear against and no room for end bearing.

Stacked openings on successive floors, which concentrates load into narrow piers.

A wide opening in a wall carrying a roof, where the roof load is the governing case rather than the masonry above.

An opening in a shear wall, which reduces the wall's ability to resist lateral load and is a different problem entirely, covered in [shear walls and lateral stability](/blog/shear-walls-and-lateral-stability-in-apartments).

Reading the crack

A horizontal crack in the mortar course immediately above a window head, with no vertical component, is almost always the lintel. Either it deflected or it corroded, and which one is usually obvious from whether the brickwork above has dropped or lifted.

Diagonal cracking from the corner of an opening is more often the wall moving, which is an [articulation](/blog/articulation-joints-in-brick-veneer-houses) or a footing question rather than a lintel one.

ACSES provides structural engineering for renovations, alterations and masonry assessment across Sydney. Get in touch.