Why brick cracks above windows

What a lintel is

Above every window and door in a brick wall, something has to hold up the brick. On most brick homes built in the last hundred years, that's a steel angle called a lintel. Its ends rest on the brick on either side of the opening.

Why rust cracks the wall

When water reaches the lintel, it rusts. Rust takes up several times more space than the steel it came from, so as it builds up, it pushes the brick above it up and out. The wall cracks at the corners of the opening, often in a stair-step pattern through the joints.

Signs to look for

• Stair-step cracks starting at the top corners of windows or doors
• A horizontal crack along the top of the opening
• Brick over the opening bulging out or sagging
• Rust stains or flaking rust on the steel
• A gap opening up between the lintel and the brick above

Why it shouldn't wait

The rust keeps growing as long as water gets to it. Cracks let in more water, which speeds things up, and over time the brick above the opening can come loose.

How it's fixed

The brick above the opening is taken down, the lintel is replaced (or cleaned and coated if the steel is still solid), and the brick is relaid with matched mortar. Where the wall allows, flashing and weep holes go in so water drains out instead of sitting on the steel.

Not every crack is a lintel

Stair-step cracks can also come from settling or foundation movement. If cracks are wide, keep growing, or show up away from windows and doors, the cause needs a closer look before anything gets patched.

More homeowner guides

• How to tell if your house needs tuckpointing
• Chimney crown vs. chimney cap: what's the difference?
• White stuff on your brick: what efflorescence means