Rusting steel lintels above windows and doors are one of the most common — and most expensive — hidden problems in Chicago's older masonry buildings. Here is how to spot the early signs and plan repairs before the wall moves.
Above every window and door opening in a masonry wall there is a horizontal support carrying the brick or stone above it. In most Chicago buildings put up between roughly 1890 and 1960 — the greystones of Logan Square, the brick two-flats of Bridgeport and Avondale, the courtyard buildings of Rogers Park — that support is a steel angle iron, usually painted and then bricked over.
Steel rusts. When it rusts it expands, and it expands with real force: corroded steel can swell to several times its original thickness. Because the lintel is trapped inside a masonry wall, that expansion has nowhere to go except into the brick and mortar sitting on top of it. This is called rust jacking, and it is the single most common structural complaint on Chicago's older housing stock.
The Chicago climate accelerates every step. Lake-effect moisture, driving rain off the lake in spring and fall, and roughly a hundred freeze-thaw cycles a season keep water moving in and out of the masonry. Road salt spray from the street adds chlorides that make corrosion faster still on ground-floor and garden-level openings.
You do not need scaffolding to do a useful first pass. Walk the building perimeter with binoculars and look at these locations in this order.
First, the front bay windows. Greystones and two-flats concentrate weight over wide bay openings, and those lintels carry the most load. Second, the openings under a downspout or a leaking gutter — wherever water has been dumping for years is where steel goes first. Third, the rear and side elevations, which almost never get looked at and rarely get maintained. Fourth, garden-level and basement window openings, where salt spray and snow pileup do their work. Fifth, the door openings at the front stoop, which take both weather and vibration. Sixth, any opening where a previous owner installed replacement windows — the tear-out often disturbs the lintel's protective coating and flashing.
On a building in Lakeview or Andersonville with a full masonry front and common brick sides, the sides usually fail first even though the front is what everyone photographs.
Lintel failure announces itself in a predictable sequence, and catching it early is the difference between a few thousand dollars and a wall rebuild.
The earliest sign is a fine horizontal crack in the mortar joint directly above a window head, running the width of the opening. Next comes displacement: the brick course above the window starts to sit slightly proud of the wall plane, which you can see by sighting along the facade from the corner rather than looking at it straight on. Then rust staining — orange-brown streaks bleeding down the brick below the lintel — appears, which means water has reached bare steel and is carrying oxide out through the joint.
Later stages are unmistakable: stepped cracking climbing diagonally from the window corners, spalled brick faces that have popped off, visible gaps where you can see daylight or the rusted steel edge itself, and windows that suddenly stick or will not close square because the opening has deformed. If you are already at that stage, stop reading and get an assessment. The load path is compromised.
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