Rusting Steel Lintels in Chicago: The Crack Above Your Window
By Affordable Tuckpointing Pros, a Chicago tuckpointing and brick repair company in business since 1996. License number MC6337.
Direct answer
A steel lintel is the angle that carries the brickwork over an opening, and when it corrodes the rust occupies more space than the steel it replaced, so it lifts the masonry sitting on it. That is what produces the horizontal crack in the joint directly above a window, often with rust staining and displaced brick. BIA treats it as a structural matter rather than maintenance, listing accumulated rust on lintels or shelf angles among the conditions that warrant investigation by a professional engineer. [2] The underlying cause is water reaching the steel, which is why flashing and weepholes matter as much as the steel itself. [1]
TL;DR
- A lintel is a structural member placed over an opening in a wall, and its prime function is to support the loads above that opening. [1]
- Corroding steel expands. The rust needs more room than the steel did, so it jacks the brick course above it and opens a horizontal crack at the head of the window.
- BIA puts accumulated rust on lintels or shelf angles on its structural list, alongside cracks over 0.075 in., cracks through multiple units and out-of-plane movement, all warranting a professional engineer. [2]
- The root cause is nearly always water management, not steel quality. BIA says continuous flashing should be installed over the angle even where galvanized or stainless steel is used. [1]
- Weeps are not optional. BIA says that regardless of whether flashing is used, weepholes should be provided in the facing at the level of the lintel. [1]
- In a climate like this one, protection is expected up front. BIA says that for harsh climates and exposures, consideration should be given to galvanized steel lintels, and that otherwise the steel will require periodic maintenance to avoid corrosion. [1]
- Not every crack over a window is rust. BIA says many cracks over openings are due to excessive deflection of the lintel from improper or inadequate design. [1]
One liner: The steel did not fail because it was weak. It failed because water got to it and nothing carried that water back out of the wall.
What is a lintel, and what is it doing over your window?
In short: It is the structural member spanning the opening, carrying the weight of the wall above so the window does not.
BIA gives the plain definition: a lintel is a structural member placed over an opening in a wall, and regardless of the material chosen, its prime function is to support the loads above the opening. [1] In brick masonry that member might be reinforced brick masonry, a brick arch, precast concrete, or a structural steel shape. [1] On the overwhelming majority of Chicago residential and small commercial buildings from the last century, it is a steel angle.
BIA describes the common configurations. A loose angle lintel is used in brick veneer and cavity wall construction, where the lintel is laid in the wall and spans the opening, and this type has no lateral support. [1] In solid masonry walls you may find combination lintels, and where openings are greater than 8 ft it may be necessary to use lintels composed of steel beams with attached or suspended plates, which allows the beam to be fully encased in masonry and fire-protected. [1] BIA notes that most building codes permit steel angle lintels for openings up to 8 ft 0 in. [1] There are also shelf angles, which in panel wall systems support the exterior wythe of brickwork and are rigidly attached to the structural frame, sometimes also acting as lintels over openings. [1]
The dimensions BIA specifies are worth knowing, because they tell you what should be there. Steel angle lintels should be at least 1/4 in. thick, with a horizontal leg of at least 3 1/2 in. for use with nominal 4 in. thick brick, and 3 in. for use with nominal 3 in. thick brick, in steel conforming to ASTM A36. [1] Bearing at each end should not be less than 3 in. [1]
From the sidewalk you usually cannot see any of it. What is visible is a painted steel edge under the top course of brick above the window, and on many buildings not even that. The lintel becomes visible when it starts to fail.
Why steel lintels rust, and why the rust moves your wall
In short: Water reaches the steel, corrosion products take up more volume than the steel did, and the masonry resting on the lintel gets pushed upward.
Steel in a masonry wall is protected by two things: a coating, and staying dry. Both are temporary in Chicago unless the wall was detailed to keep water moving outward. Once the coating is compromised and water is arriving at the steel regularly, corrosion begins, and the corrosion product is the problem rather than the loss of metal. Rust occupies more volume than the steel it formed from. Confined between a bearing course below and loaded brickwork above, that expansion has one direction to go, and it lifts.
That is why the damage pattern is so distinctive and so readable. You get a horizontal crack in the bed joint immediately above the window head, often running the full width of the opening and sometimes stepping up at the ends. You get rust-coloured staining bleeding down the brick or out of the joint. You may get brick that is visibly displaced outward or sitting proud of the surrounding wall, and in advanced cases individual units that have cracked through. BIA lists corrosion of concealed materials among the observed conditions in its distress table, alongside moisture-related stains and cracked units. [2]
BIA is explicit about the severity classification. Among conditions it says are structural and outside the scope of routine maintenance, warranting an investigation by a professional engineer to determine the cause and recommend the repair, it lists accumulated rust on lintels or shelf angles, together with cracks in brick masonry exceeding 0.075 in. in width, cracks through multiple brick units, cracks following a stepped or diagonal pattern, widespread spalled brick, out-of-plane movement of brick masonry or other wall elements, and neutral or negative slope on masonry sills and water tables. [2] If you are seeing rust staining and a lifted course above an opening, that is not a tuckpointing item you can defer to next season.
The severity also depends on what the lintel is carrying. A loose angle over a basement window in a veneer wall is a different proposition from a shelf angle carrying an entire wythe. BIA notes that the loose angle type has no lateral support, and that shelf angles support the exterior wythe and are attached to the structural frame. [1] The engineer’s job is partly to establish which one you have.
The real cause: flashing and weeps, not the steel
In short: BIA requires continuous flashing over the angle and weepholes at lintel level even when the steel is galvanized or stainless, because the design assumption is that water will get into the wall.
This is the part that changes how you should read a repair quote. Brick veneer and cavity walls are not built to be watertight at the face. BIA describes drainage-type walls as designed to accommodate water penetration of the exterior brickwork without damage to the interior components, through the wall’s drainage system. [3] Water is expected to get in. What keeps the lintel alive is the system that collects that water and sends it back out.
BIA’s requirement is unambiguous and it does not treat corrosion-resistant steel as a substitute. Even where galvanized or stainless steel angles are used for lintels in cavity and veneer walls, continuous flashing should be installed over the angle, placed between the steel and the exterior masonry facing material to collect and divert moisture to the outside through weepholes. [1] And then, separately: regardless of whether flashing is used, weepholes should be provided in the facing at the level of the lintel to permit the escape of any accumulated moisture. [1]
Read those two sentences as a checklist for your own building. Are there weeps in the brick course at the level of the lintel above your windows? On a lot of Chicago buildings the answer is no, either because they were never installed or because they have been pointed shut during a previous repointing job. BIA’s inspection checklist lists missing or clogged weeps as a condition to record, and its distress table names missing or clogged weeps and missing or damaged flashing among the probable causes of the conditions you are seeing. [2] Its maintenance instruction is to carefully open clogged weeps to ensure that existing flashing is not damaged, and where weeps do not exist, to carefully drill new weeps, again without damaging any flashing that is there. [2]
Flashing has its own service life, which is shorter than the wall’s. BIA estimates 20 to 75 years for metal coping and flashing and 5 to 25 years for plastic flashing, against 100 to 150 years and beyond for the brick. [2] So on a building of any age, a rusted lintel and failed or absent flashing usually arrive together, and replacing the steel without addressing the flashing restarts the same clock.
BIA also sets the expectation for a climate like ours at the specification stage: for harsh climates and exposures, consideration should be given to the use of galvanized steel lintels, and if this is not done, then the steel lintels will require periodic maintenance to avoid corrosion. [1] That is the choice in a sentence. Either the steel is protected, or somebody has to keep maintaining it, and on most buildings nobody does.
When the crack above the window is not rust
In short: Deflection produces cracks over openings too, and BIA gives numeric limits that distinguish a lintel that is bending from one that is corroding.
Not every crack at a window head is a corrosion story, and assuming it is can send you into the wrong repair. BIA states that many of the cracks which appear over openings in masonry walls are due to excessive deflection of the lintels resulting from improper or inadequate design, and that the structural design of lintels should not involve rule-of-thumb methods or the arbitrary selection of structural sections without careful analysis of the loads and stresses. [1]
BIA sets serviceability limits you can ask an engineer to check against. Lintels supporting masonry should be designed so that deflection does not exceed 1/600 of the clear span, nor more than 0.3 in., under the combined superimposed live and dead loads. [1] Where torsion is present, rotation of the lintel should be limited to 1/16 in. maximum under the same combined loads. [1] Those are small numbers, and that is the point: masonry is brittle and it cracks long before the steel is in any danger.
The visual distinction is usually available. Rust jacking tends to come with staining, with the crack opening widest at the joint immediately above the steel, and with brick pushed outward or upward. Deflection tends to produce cracking that reflects sagging in the middle of the span, often without rust staining, and it frequently shows up early in a building’s life or after loads above the opening changed. Differential movement is a third cause entirely; BIA’s distress table lists differential movement separately among the probable causes of cracked units. [2]
There is also the possibility that the crack over the opening is telling you about something other than the lintel. Stepped or diagonal cracking that happens to pass a window is on BIA’s structural list and can indicate settlement or movement elsewhere in the structure. [2] This is exactly why BIA’s guidance for that category of condition is to get an engineer to determine the cause before anybody specifies a repair. [2]
What lintel replacement actually involves
In short: The brickwork above the opening is supported, the corroded steel is removed, new protected steel goes in with flashing and weeps, and the masonry is rebuilt.
Lintel replacement is a shoring job before it is a steel job. The masonry above the opening has to be carried while the member carrying it is removed, which is why this work is not comparable to repointing either in method or in cost. BIA’s guidance for the related case of replacing flashing in an existing wall gives the flavour of the sequencing: repair or replace damaged flashing in alternate 2 to 5 ft sections, and use temporary bracing to install longer sections. [2] The wall is taken apart in lengths that remain stable, not all at once.
The brick over the opening is removed and, wherever possible, salvaged for reinstatement, because matching existing Chicago brick is difficult. BIA’s instruction for replacement units applies here: when selecting new brick to match the appearance of existing brick, use mock-ups or sample panels, and do the same when selecting mortar to match the existing joints. [2] Units are removed by breaking the damaged ones to assist removal and cutting out the remaining mortar without damaging adjacent units. [2]
The new steel should meet the specification rather than whatever fits: at least 1/4 in. thick, with a horizontal leg of at least 3 1/2 in. for nominal 4 in. brick, ASTM A36, with bearing of at least 3 in. at each end. [1] For this climate, galvanized. [1] Then the water management that was missing the first time: continuous flashing over the angle, placed between the steel and the exterior facing, and weepholes in the facing at lintel level. [1]
Rebuilding follows normal masonry practice, with the pointing done in multiple quarter-inch lifts, each tooled when thumbprint hard, in a mortar compatible with the surrounding wall. BIA recommends prehydrated Type N, O or K mortar for repointing work. [2] Getting that mix right matters as much here as anywhere else on the building, because a hard mortar will simply move the damage into the brick instead; NPS says a mortar stronger in compressive strength than the masonry units relieves stresses through the units, causing cracking and spalling. [4] Our post on why Chicago brick spalls covers that failure in full.
Expect the scope to extend beyond the single opening. If one lintel on an elevation has corroded because there was no flashing and no weeps, the others on that elevation were built the same way. An honest assessment prices the ones that are failing now and tells you where the rest are in the queue. Our lintel replacement and masonry repair pages cover how we scope it.
Catching it before the wall moves
In short: Seasonal inspection with binoculars, looking specifically at window heads, sills and weeps, is what keeps a lintel from becoming a rebuild.
BIA frames lintels as one of the components that need watching precisely because neglecting them damages other things. It notes that brickwork which is properly designed, detailed and constructed will require very little maintenance, but that other components incorporated in the brickwork, such as caps, copings, sills, lintels and sealant joints, may require periodic inspection and repair, and that neglecting maintenance of these components may lead to deterioration of other elements in the wall. [2]
The recommended habit is seasonal. BIA advises performing periodic inspections, preferably each season, so that the behaviour of building materials in various weather conditions can be observed, and using binoculars along with adjacent roof areas and balconies to permit close-range observation of conditions at upper floors. [2] For lintels specifically, the upper-floor openings are the ones that go unnoticed longest, because nobody is standing under them.
What to look for at each opening, drawn from BIA’s own checklist and distress table: rust staining on the brick or in the joint, a horizontal crack in the bed joint above the head, cracked or loose units above the opening, brick that is out of plane, missing or clogged weeps at lintel level, deteriorated or torn sealant around the window, damaged or missing flashing, and inadequate slope on the sill below. [2] Interior surveys matter too; BIA suggests noting stains or damage to finishes that may indicate water ingress. [2]
Keep the records. BIA recommends that inspection records including conditions and comments be kept to identify changes in materials, and that repair documentation include before-and-after photographs, so future inspections can gauge when repairs were last done and when they will become necessary again. [2] On lintels that is genuinely useful, because the tell is the rate of change. A hairline crack over a window that is the same width in three consecutive spring photographs is a different problem from one that has doubled.
Lintel questions Chicago building owners ask
What causes a horizontal crack above a window?
Most often a corroding steel lintel. The rust takes up more volume than the steel did and lifts the brick above it, opening the bed joint at the window head. BIA lists accumulated rust on lintels or shelf angles among conditions warranting a professional engineer. [2] Excessive lintel deflection is the other common cause. [1]
Is a rusted lintel a structural problem?
BIA treats it as one. Accumulated rust on lintels or shelf angles appears on its list of conditions that are structural, outside the scope of routine maintenance, and warrant investigation by a professional engineer. [2]
Can a rusted lintel be repaired instead of replaced?
It depends on how far the corrosion has gone and what the member is carrying, which is what the engineering assessment establishes. [2] Whatever is done to the steel, the flashing and weeps have to be addressed or water keeps arriving at it. [1]
Why did the lintel rust in the first place?
Water reached the steel and was not carried back out. BIA requires continuous flashing over the angle even where galvanized or stainless steel is used, and weepholes in the facing at lintel level regardless of whether flashing is present. [1] Missing or clogged weeps and missing or damaged flashing are on its list of probable causes of masonry distress. [2]
Should lintels be galvanized?
In this climate, yes. BIA says that for harsh climates and exposures, consideration should be given to galvanized steel lintels, and that otherwise the steel will require periodic maintenance to avoid corrosion. [1]
What size should a steel lintel be?
BIA specifies at least 1/4 in. thick, with a horizontal leg of at least 3 1/2 in. for nominal 4 in. brick and 3 in. for nominal 3 in. brick, in ASTM A36 steel, with bearing of not less than 3 in. at each end. [1] Sizing for the actual span and load is an engineering calculation, not a rule of thumb. [1]
How much deflection is acceptable in a lintel?
BIA says deflection should not exceed 1/600 of the clear span, nor more than 0.3 in., under the combined superimposed live and dead loads, and that rotation where torsion is present should be limited to 1/16 in. [1]
Do I need weepholes above my windows?
BIA says yes. Regardless of whether flashing is used, weepholes should be provided in the facing at the level of the lintel to permit the escape of any accumulated moisture. [1] If yours have been pointed shut, BIA says to carefully open them without damaging existing flashing. [2]
How long should flashing last?
BIA estimates 20 to 75 years for metal coping and flashing and 5 to 25 years for plastic flashing, against 100 to 150 years and beyond for brick in walls. [2]
How often should I check the lintels?
BIA recommends periodic inspections, preferably each season, using binoculars and adjacent roofs or balconies to get a close view of upper floors. [2] Upper-storey openings are the ones that go unnoticed longest.
Stats box
| Figure | Value | Source | Date |
|---|---|---|---|
| Minimum steel angle lintel thickness | 1/4 in. (6 mm) | BIA Technical Note 31B [1] | Revised May 1987 |
| Minimum horizontal leg, nominal 4 in. brick | 3 1/2 in. (90 mm) | BIA Technical Note 31B [1] | Revised May 1987 |
| Minimum bearing length at each end | 3 in. (75 mm) | BIA Technical Note 31B [1] | Revised May 1987 |
| Deflection limit under combined live and dead load | 1/600 of clear span, max 0.3 in. (8 mm) | BIA Technical Note 31B [1] | Revised May 1987 |
| Rotation limit where torsion is present | 1/16 in. (1.5 mm) | BIA Technical Note 31B [1] | Revised May 1987 |
| Opening width most codes allow steel angle lintels for | Up to 8 ft 0 in. (2.4 m) | BIA Technical Note 31B [1] | Revised May 1987 |
| Crack width indicating a structural issue | Over 0.075 in. (2 mm) | BIA Technical Note 46 [2] | December 2017 |
| Estimated time to repair, metal coping and flashing | 20 to 75 years | BIA Technical Note 46, Table 1 [2] | December 2017 |
| Estimated time to repair, plastic flashing | 5 to 25 years | BIA Technical Note 46, Table 1 [2] | December 2017 |
| Estimated time to repair, metal anchors and ties | 15+ years | BIA Technical Note 46, Table 1 [2] | December 2017 |
| Flashing replacement section length | Alternate 2 to 5 ft (610 mm to 1.52 m) sections | BIA Technical Note 46 [2] | December 2017 |
Definition bank
| Term | Definition |
|---|---|
| Lintel | A structural member placed over an opening in a wall, whose prime function is to support the loads above the opening. [1] |
| Loose angle lintel | A steel angle laid in the wall to span an opening in brick veneer or cavity wall construction. BIA notes this type has no lateral support. [1] |
| Shelf angle | An angle rigidly attached to the structural frame that supports the exterior wythe of brickwork, sometimes also acting as a lintel over openings. [1] |
| Rust jacking | Displacement of masonry caused by corrosion products occupying more volume than the steel they formed from. BIA lists accumulated rust on lintels or shelf angles as a structural indicator. [2] |
| Flashing | A membrane installed over the lintel, between the steel and the exterior facing, to collect water in the wall and divert it outward. BIA requires it even with galvanized or stainless angles. [1] |
| Weephole | An opening in the facing at lintel level that lets accumulated moisture escape. BIA says to provide them regardless of whether flashing is used. [1] |
| Drainage-type wall | A wall such as a brick veneer or cavity wall designed to accommodate water penetration of the exterior brickwork and drain it back out. [3] |
| Deflection limit | The serviceability ceiling for a lintel supporting masonry: 1/600 of the clear span and no more than 0.3 in. under combined superimposed live and dead loads. [1] |
| ASTM A36 | The structural steel specification BIA names for steel angle lintels. [1] |
| Structural indicator | A condition BIA says warrants a professional engineer, including accumulated rust on lintels or shelf angles, cracks over 0.075 in., cracks through multiple units, stepped or diagonal cracking and out-of-plane movement. [2] |
Entity cards
Steel lintel
| Property | Value |
|---|---|
| Function | Supports the loads above the opening [1] |
| Typical material | ASTM A36 structural steel [1] |
| Minimum thickness | 1/4 in. (6 mm) [1] |
| Minimum horizontal leg, 4 in. brick | 3 1/2 in. (90 mm) [1] |
| Minimum end bearing | 3 in. (75 mm) [1] |
| Deflection limit | 1/600 of span, max 0.3 in. [1] |
| Recommended in harsh climates | Galvanized [1] |
Rust jacking
| Property | Value |
|---|---|
| Visible sign | Horizontal crack in the joint above the opening |
| Secondary sign | Rust staining and displaced or cracked brick [2] |
| BIA classification | Structural, warrants a professional engineer [2] |
| Root cause | Water reaching the steel and not draining out [1] |
| Prevented by | Flashing over the angle plus weeps at lintel level [1] |
Lintel flashing and weeps
| Property | Value |
|---|---|
| Flashing required when | Always, even with galvanized or stainless angles [1] |
| Flashing position | Between the steel and the exterior facing [1] |
| Weeps required when | Regardless of whether flashing is used [1] |
| Weep location | In the facing at the level of the lintel [1] |
| Metal flashing service life | 20 to 75 years [2] |
| Plastic flashing service life | 5 to 25 years [2] |
| If weeps are clogged | Open carefully without damaging flashing [2] |
Lintel deflection
| Property | Value |
|---|---|
| Named by BIA as | A cause of many cracks over openings [1] |
| Deflection ceiling | 1/600 of clear span, max 0.3 in. [1] |
| Rotation ceiling | 1/16 in. (1.5 mm) [1] |
| Usual origin | Improper or inadequate design [1] |
| Distinguishing sign | Cracking without rust staining |
Reading the opening before anyone prices the repair
In short: Ask whether there is flashing over the lintel and weeps at its level, and you have asked the question that decides whether the new steel lasts.
A rusted lintel is rarely a steel problem. It is a drainage problem that ended at the steel. BIA requires continuous flashing over the angle even where the steel is galvanized or stainless, and weepholes in the facing at lintel level regardless of whether flashing is used. [1] Where both of those are missing, corrosion is the expected outcome rather than bad luck.
So when you get a quote, look for three things in it: that somebody has established whether the crack is corrosion or deflection, that the replacement steel is specified and protected for this climate, and that flashing and weeps are in the scope rather than assumed. [1] [2] If the quote replaces steel and rebuilds brick without mentioning where the water goes, it has priced the symptom.
And because BIA puts accumulated rust on lintels in the structural column, this is one of the few masonry conditions where the right first call may be an engineer rather than a mason. [2] If you want us to look at the opening and tell you which one you need, get a free quote from our team.
Sources
- Brick Industry Association, Technical Notes 31B, “Structural Steel Lintels”, revised, reissued May 1987. https://www.gobrick.com/media/file/31b-structural-steel-lintels.pdf
- Brick Industry Association, Technical Note 46, “Maintenance of Brick Masonry”, December 2017. https://www.gobrick.com/media/file/46-maintenance-of-brick-masonry.pdf
- Brick Industry Association, Technical Note 6A, “Colorless Coatings for Brick Masonry”, August 2008. https://www.gobrick.com/media/file/6a-colorless-coatings-for-brick-masonry.pdf
- National Park Service, Preservation Brief 2, “Repointing Mortar Joints in Historic Masonry Buildings”, Mack and Speweik, rev. 1998. https://www.nps.gov/orgs/1739/upload/preservation-brief-02-repointing.pdf