Someone on the board noticed it from across the street: cracks stepping up from the corners of the windows, and a rust streak under one of them. Your super says it's looked like that for years. Your QEWI may already have it in the report.

The cause is usually inside the wall, in steel nobody can see from the sidewalk. For how we carry out the repair, see lintel and shelf angle repairs.

What are lintels and shelf angles?

A lintel is the beam over a window or door opening that carries the masonry above it. On a lot of New York brick buildings it's a steel angle, sometimes a pair of them, set into the wall behind the face brick.

A shelf angle (also called a relieving angle) is a steel angle fastened to the building's frame at a floor line, and it carries the brick for the story above. You'll find them on steel- and concrete-frame buildings with brick façades. Older load-bearing masonry buildings usually have lintels and no shelf angles.

Both are buried in the wall. You almost never see the steel itself, only what it's doing to the brick.

Why does rusting steel crack brick?

Steel rusts when water and oxygen reach it. Rust occupies much more room than the steel it came from, and it forms in layers between the steel and the masonry. As the layers build, they push.

Brick and mortar are strong when squeezed and weak when pulled. So when rust pushes up on the brick above a lintel, the joints crack and the brick lifts. That's rust jacking.

The water usually comes from above. Lintels and shelf angles are supposed to be protected by through-wall flashing: a membrane or metal sheet above the steel that catches water inside the wall and sends it out through weeps at the face. On many older buildings that flashing has failed, was never installed, or stops short of the lintel ends, so water runs straight onto the steel. Open mortar joints and failed sealant at the window head let in more.

From there it feeds itself. The crack lets in more water, the steel rusts faster, and the crack widens. Every winter, freeze and thaw speeds it along.

Shelf angles often have a second problem. Brick grows slightly over its life as it takes on moisture, while a concrete frame shortens. Without a soft joint under the shelf angle to take up that movement, the brick gets squeezed between floors and cracks or bows. When we open up a floor line, rust and squeeze are often working together.

What do the cracks look like?

  • stair-step cracks running up from the corners of window heads, following the mortar joints
  • a horizontal crack along the line of the lintel, a course or two above the window
  • cracked or lifted brick at the ends of the lintel, where it bears on the wall
  • brick bulging or displaced along a floor line, often with a horizontal crack (shelf angles)
  • rust staining bleeding out of the joints below the steel
  • brick faces spalling off along the lintel line
  • leaks at window heads, and head sealant that keeps failing

Stair-step cracks at window corners can have other causes, settlement among them. Rust staining and lifted brick at the lintel ends are the strongest signs that the steel is the problem.

Why does it matter for your FISP report?

QEWIs look for these conditions during the close-up inspection, and how they're classified is your QEWI's call. Early rust with minor cracking often goes on a SWARMP list with a repair date. Displaced or loose brick over an opening, where pieces could fall, is the kind of condition that can be filed Unsafe. That means immediate public protection and a 90-day correction deadline.

A lintel that was SWARMP last cycle and wasn't fixed must be filed as Unsafe at the next inspection, with a $2,000 penalty. SWARMP vs. Unsafe goes through how that works.

How are rusting lintels and shelf angles repaired?

That depends on how much steel is left, and the only way to know is to open the wall.

Treat in place

When the steel still has most of its section, we take down the brick above far enough to expose it. The steel is cleaned to bare metal, your engineer checks what's left, and it gets a rust-inhibiting coating system. New through-wall flashing goes in with end dams and a drip edge, weeps are added, and the brick goes back up.

Replace

When too much steel is gone, the masonry above is shored, the brick and the old steel come out, and new steel goes in: hot-dip galvanized or stainless, as your engineer specifies. Then come new flashing and weeps, and brick and mortar matched to the wall around them. Our masonry restoration page covers how we match.

Shelf angles

Same principle, but the steel is fastened to the frame and runs the length of the floor line, so the work goes in sections with temporary support. Engineers often add or restore a soft joint under the angle so the brick has room to move.

Whichever repair it is, it follows your engineer's details. On an individual landmark or in a historic district, it also needs an LPC permit before work begins.

Why doesn't patching the brick hold?

Because the cause is still there. The steel keeps rusting behind the new mortar or caulk, the rust keeps growing, and the crack comes back. Replacing cracked bricks without exposing the steel just puts new brick under the same pressure. Each round of patching only postpones the repair, and it's usually a bigger job by the time it happens.

If a proposal says "point and seal" for a rust-jacked lintel, ask what happens to the steel.

Sources

This article is general information, not legal advice. Your QEWI and engineer confirm how the rules apply to your building.