Recognizing Lintel Failure: Cracks Above Windows in Masonry Buildings

By John Screen, President and Founder of JMS Masonry & Restoration in Boston, MA

Our team has been doing masonry restoration work in Boston for many years, and one of the most commonly misinterpreted warning signs I find on older brick buildings is cracking right above windows and door openings. Owners see the crack, have their concerns, think about calling a specialist but ultimately chalk it up to “settling.”

Sometimes that’s true but a lot of times is not. What you’re really seeing could be a failing lintel and that’s an entirely different discussion.

TL;DR: Cracks above windows in brick or stone buildings are often the result of a failed metal or stone lintel, which is the structural element that supports the wall load over the opening. Lintel failure doesn’t remain cosmetic for long if you don’t act on it.

What Is a Lintel and Why Does It Collapse?

A lintel is the horizontal beam (steel angle iron, stone, or occasionally concrete) that spans just above a window or door opening and supports the weight of masonry above. Without it, there’s no transfer of that load through the void.

The most common trouble spot in Boston-area buildings, especially those built roughly between 1880 and 1960, is steel lintels. Steel expands when it rusts, and even a few millimeters of expansion driven by this process creates incredible pressure inside the masonry. The brick above begins to crack, the mortar joints open up and finally the whole assembly can shift.

Stone lintels, however, fail differently. Generally by failing under load, or erosion of the bearing faces at either end.

Still, regardless of type, both have one thing in common: the damage above them becomes apparent before the lintel itself appears obviously wrong.

How Can You Tell if Cracks Above a Window Is Serious?

Not every crack over a window spells structural trouble, but there are patterns that are difficult to ignore once you know what you’re seeing.

Cracking in the mortar joints or stair-step cracks

This is the classic pattern. When a lintel deflects or shifts, it doesn’t cause the masonry above to fall straight down. Instead, it separates along its weakest path (the mortar). You have a diagonal crack that staircase up the bed and head joints. If you spot this radiating outwards from the corners of a window opening, we strongly advise you to take it seriously.

An apparent bow or sag in the brick coursing

Step back from the building and focus on the horizontal brick courses running above the window. They should be straight. Any detectable curve or dip is the lintel notifying you that it no longer supports the geometry for which it was constructed.

Rust staining beneath a window head

Brown or orange staining in the mortar directly at the window head is nearly always iron oxide rust working its way out of a steel lintel. The lintel itself might be structurally intact, or it could be halfway gone. Either way, moisture is trapped inside the wall assembly, and that’s not a problem that just gets better with time. It needs to be addressed.

Gaps opening between the window frame and the masonry

Windows (and doors) are placed in openings that were framed to a particular size. The rough opening also changes if the masonry above moves and the lintel deflects. Gaps form, windows begin to stick, and in the worst cases, the glass itself can crack under the racking strain.

Why You Shouldn’t Ignore Lintel Failure

The short answer: Every season you wait, the repair gets more expensive and more invasive.

A lintel that is caught early (before the surrounding masonry has been forced out of alignment significantly) can usually be replaced without disturbing more than a few brick courses above the opening. The old brick gets numbered, removed and stored aside while a new lintel is put in and then the old brick is reset. And if the brick is in good condition, you may not even be able to tell that work was done.

Wait too long, and the settlement proliferates upward and outward. Lintels on openings adjacent to the stressed elements may also be stressed. The water has had months or years to move deeper into the wall assembly where it may reach wood framing, sheathing or interior finishes. What began with a lintel switch has now evolved into a partial wall rebuild.

We’ve seen both lintel failure scenarios in the Greater Boston area. The early call is definitively the better outcome, from both financial and structural perspectives.

Is Tuckpointing the Solution to a Failing Lintel?

This is a question that deserves a direct answer, because many property owners are given estimates on tuckpointing when the problem in fact is structural.

Tuckpointing (removing decaying mortar and replacing it) is real and necessary maintenance. It helps keep water out and makes the masonry last longer, but it does not fix a lintel. If the underlying steel is still rusting and expanding, new mortar will just crack again.

How to Find a Qualified Masonry Contractor in Boston?

A lot of Boston’s building stock is brick, and it’s old. That means there’s no shortage of people who want to work on it. Locating someone who really knows historic masonry restoration requires a bit more effort.

Ask how much experience they have with your type of building and whether they’d recommend a structural engineer to consult before work begins. A contractor with confidence in his assessment will not hesitate to call one in if the situation calls for it.

After working in the Boston area for years at JMS Masonry & Restoration, we are a perfect fit to undertake this work. If you’re noticing cracks above windows on your building, we’ll be happy to take a look and provide you with a straightforward answer about what you are dealing with.

Contact JMS Masonry & Restoration today for a free estimate!