The Crack Above Your Window Is Probably Not Settlement
Usually not. In a brick or brick veneer house of roughly the 1920s to 1950s, a step crack running up from the top corner of a window, a door or a garage opening is normally the steel lintel behind it corroding, and rust scale can occupy up to ten times the volume of the metal it consumed. Look for a rust stain and a brick course that is no longer level, and do not fill it: sealing the crack keeps water against the steel and the steel keeps growing.
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How a crack over an opening actually progresses
Water reaches the steel
InvisibleMissing or failed flashing above the opening, or open joints in the courses over it. The steel is enclosed by masonry, so corrosion can be concealed within the wall.
Rust scale forms and swells
Still invisibleRust scale can occupy up to ten times the volume of the original metal. One measured beam flange had gone from three eighths of an inch thick to one and five eighths.
The brick course above lifts
First visible signA course that no longer reads level along its length, and often a rust stain bleeding down out of the joint at one end of the lintel.
A step crack opens from the top corner
What gets called settlementThe National Park Service lists corrosion of iron and steel wall reinforcement among the causes of cracking, and says cracking around openings results from deflection or failure of the lintel.
The crack lets in more water
The loop closesCracks and gaps allow more water into the wall, increasing the potential for further corrosion. Filling the crack seals in the water that is already there.
Deborah Slaton and David S. Patterson of Wiss, Janney, Elstner Associates in The Construction Specifier, and the National Park Service on common problems with brick masonry.
Corrosion does not thin a lintel, it swells it
The steel angle over your window is doing two jobs: carrying the brick above the opening, and staying dry. When it stops staying dry it does not simply get thinner. Two engineers from Wiss, Janney, Elstner Associates, writing in The Construction Specifier, describe unprotected mild steel oxidizing rapidly when exposed to moisture and producing rust scale, an iron oxide, that can occupy up to ten times the volume of the original metal. That expansion has nowhere to go, because the steel is boxed in by brick on the outside and loaded by masonry above, so the force goes into the wall. The trade name for it is rust jacking. The same article publishes measurements rather than adjectives: one beam flange that started at three eighths of an inch had expanded to one and five eighths of an inch, more than four times its original thickness, and in a second case rust jacking had displaced the adjacent masonry by three quarters of an inch. Three quarters of an inch of movement in a brick wall is not a hairline anything.
How to tell a lintel crack from a foundation crack
Where the crack starts is the first clue. A step crack that runs diagonally up and away from the top corner of a window, a door or a garage opening is behaving like something pushing out from that opening. A crack that begins near the foundation and travels upward is behaving like something moving underneath. The National Park Service lists the corrosion of iron and steel wall reinforcement among the causes of cracking in brick masonry, alongside differential settlement of foundations, drying shrinkage, thermal and moisture movement, freeze-thaw cycles, the expansion of salts and the bulging or leaning of walls. On openings it is specific: cracking or displacement of masonry around openings results from the deflection or failure of the lintels or arches that span them, and iron and steel lintels cause cracking as they deflect or rust over time. Two more tells are free to check. A rust stain bleeding down out of the joint at either end of the lintel, and a brick course above the opening that is no longer level. Put your eye close to the wall and sight along the course, and a lifted course is usually obvious.
Why filling the crack makes it worse
This is the mistake that costs people the most money, because it feels like responsible maintenance. The crack is the route water is taking, and water is what feeds the corrosion. Seal the crack from the outside and the water already inside stays inside, against the steel, where the feedback loop the same engineers describe takes over: the increased porosity of a corroded surface traps and holds moisture, which leads to further corrosion, and the cracks and gaps that corrosion opens allow more water in, increasing the potential for further corrosion again. Meanwhile the steel is still growing, so the joint you filled reopens, usually within a season or two, and the second failure is wider than the first. On prevention the same article is clear about what does work, and it is undramatic: limit the rate and extent of corrosion by keeping the exterior wall in serviceable condition so less water infiltrates it, which typically means repointing masonry joints, installing sealant repairs where they belong, and repairing cracks in the masonry regularly. The order matters. Water off the steel first, appearance last.
Watch it through one season before you spend anything
Not every crack over an opening is corrosion, and visible rust is not automatically a structural failure, so there is a genuinely useful thing to do that costs nothing. The National Park Service advises monitoring a crack over a period of time to see whether it is active, and notes that thermal cracks are normally cyclical, opening and closing with the season, growing wider in cold weather and narrower in hot weather. A crack that is noticeably wider in February and closes up in August is behaving thermally, and the guidance there is that active cracks should be sealed with a flexible sealant while inactive cracks may be pointed. Mark each end of the crack with a pencil line and date it, photograph it with a coin beside it for scale, and repeat in six months. On the steel itself, the engineers note that significant accumulation of rust scale does not necessarily mean enough original material has been lost to render the member inadequate, and that section loss of 10 to 20 percent is often cited as the threshold at which further assessment of the element should be conducted. So a rust stain is a reason to look properly, not a reason to panic. What it is never a reason to do is fill the crack and hope.
What actually stops it is getting the water off the steel
Flashing. The Brick Industry Association's technical note on structural steel lintels states that there must always be a mechanism to channel the water present in a wall to the outside, and that even where galvanized or stainless steel angles are used in cavity and veneer walls, continuous flashing should be installed over the angle, between the steel and the exterior masonry facing, to collect and divert moisture out through weepholes. It adds that weepholes should be provided at the level of the lintel whether or not flashing is used. New York's own residential code says the same thing in its own language. Section R703.8.5 requires flashing at points of support including shelf angles and lintels, section R703.4 requires approved corrosion-resistant flashing at exterior window and door openings, and section R703.8.6 requires weepholes in the outside wythe at a maximum spacing of 33 inches on center, not less than three sixteenths of an inch in diameter, immediately above the flashing. That last one you can verify from your own yard by counting. On maintenance the Brick Industry Association is direct: in harsh climates and exposures consider galvanized lintels, and if that is not done, steel lintels will require periodic maintenance to avoid corrosion.
The Syracuse suburbs built when steel angles became standard
Rust jacking needs three things, bare steel, water and cycles, and this metro supplies the last two generously. Under the 1991 to 2020 climate normals the daily minimum temperature at Syracuse falls to 32 degrees Fahrenheit or below on 129.5 days of a normal year, while the daily maximum stays below 32 on only 45.7 days. The difference, roughly 84 days, is days on which the temperature crosses freezing in both directions rather than sitting below it, and every crossing is another chance for water inside a wall to expand. The steel is a question of era rather than of town. Ranked by the share of housing built between 1940 and 1959, when steel angle lintels over openings became standard in brick and brick veneer houses, the county reorders itself completely: Galeville at 60.7 percent, Seneca Knolls at 58.9, Mattydale at 54.6, Westvale at 51.3, Lyncourt at 47.1, Fairmount at 42.7 and North Syracuse village at 38.5, against 23.3 percent for the City of Syracuse itself. If you live in the postwar ring rather than the prewar core, this is your mechanism rather than the mortar one.
When it is not corrosion at all
Two other explanations are worth ruling in or out before anybody quotes. The first is deflection rather than rust. The Brick Industry Association states that many of the cracks which appear over openings in masonry walls are due to excessive deflection of the lintel resulting from improper or inadequate design, and sets its serviceability limit at one six-hundredth of the clear span and not more than three tenths of an inch under combined superimposed live and dead loads. A lintel that was undersized when it went in will sag under load with very little rust to show for it, and that is a different repair. The second is that the corrosion is real but it is somewhere else. The same engineers note that this is particularly the case for masonry buildings constructed in the early 1900s, where unprotected structural steel is often in contact with exterior wall construction and ongoing corrosion may be concealed within the wall, affecting beams, columns, lintels and anchorages in the exterior wall assembly. Either way the useful next step is somebody with a ladder and a straightedge rather than a tube of sealant. Tell us the address and what the crack is doing, and we will put it in front of licensed, insured contractors who do this work.
Sources used in this guide
Writing in The Construction Specifier, two engineers from Wiss, Janney, Elstner Associates state that unprotected mild steel oxidizes rapidly when exposed to moisture, that this oxidation produces rust scale which is an iron oxide, and that rust scale can occupy up to 10 times the volume of the original metal. They add that the increased porosity of the corroded surface can trap or hold moisture, leading to further corrosion, and that the forces exerted by corrosion can cause cracking and spalling of adjacent masonry, commonly referred to as rust jacking. The resulting cracks and gaps in the masonry can allow more water into the wall, increasing the potential for further corrosion.
Source: Deborah Slaton and David S. Patterson, AIA, both of Wiss, Janney, Elstner Associates, Expanding on structural steel, Failures column, The Construction Specifier, Construction Specifications Institute, December 7 2018, accessed 2026-09-10
The same article publishes two measured examples. In one, corrosion of a beam flange advanced to the point where the original 3 eighths of an inch thick flange had expanded to 1 and 5 eighths of an inch, more than four times its original thickness. In another, rust jacking from an expanding corrosion product on a steel beam had displaced the adjacent masonry by 3 quarters of an inch.
Source: Deborah Slaton and David S. Patterson, AIA, both of Wiss, Janney, Elstner Associates, Expanding on structural steel, Failures column, The Construction Specifier, Construction Specifications Institute, December 7 2018, accessed 2026-09-10
The National Park Service page on common problems with brick masonry lists the corrosion of iron and steel wall reinforcement among the causes of cracking, alongside differential settlement of foundations, drying shrinkage, thermal and moisture expansion and contraction, improper support over openings, the effects of freeze-thaw cycles, expansion of salts, and the bulging or leaning of walls. On openings specifically it states that cracking or displacement of masonry around openings results from the deflection or failure of the lintels or arches that span them, that in older masonry walls with wood lintels cracking occurs as the wood sags or decays, and that iron and steel lintels also cause cracking as they deflect or rust over time. It states that correcting such problems usually means replacing failed components and rebuilding the area around the opening with additional reinforcing.
Source: National Park Service, Common Problems with Brick Masonry, accessed 2026-09-10
On prevention, the article states that while preventing corrosion-related damage to steel members engaged within a masonry exterior wall can be challenging, the rate and extent of corrosion can be limited by maintaining the exterior wall in serviceable condition to minimize the amount of water infiltrating the wall, and that such maintenance typically includes repointing masonry joints, installing sealant repairs as appropriate, and repairing cracks in the masonry regularly.
Source: Deborah Slaton and David S. Patterson, AIA, both of Wiss, Janney, Elstner Associates, Expanding on structural steel, Failures column, The Construction Specifier, Construction Specifications Institute, December 7 2018, accessed 2026-09-10
On thermal cracking the National Park Service states that although masonry can deform elastically over long periods to accommodate small amounts of movement, large movements normally cause cracking, and that thermal cracks are normally cyclical and will open and close with the season, growing wider in cold weather and narrower in hot weather. It advises monitoring such cracks over a period of time to see whether they are active, and states that active cracks should be sealed with a flexible sealant while inactive cracks may be pointed.
Source: National Park Service, Common Problems with Brick Masonry, accessed 2026-09-10
The article states that significant accumulation of rust scale, while visually notable and potentially damaging to masonry in contact with the corroding steel, does not necessarily mean enough original material has been lost to render the member structurally inadequate, and that section loss of 10 to 20 percent is often cited as the threshold at which further assessment of the element should be conducted. Where rust scale accumulation is extensive, the corrosion product must be removed to determine the actual section loss, and both the location and the extent of the corrosion decide whether repair or replacement is needed.
Source: Deborah Slaton and David S. Patterson, AIA, both of Wiss, Janney, Elstner Associates, Expanding on structural steel, Failures column, The Construction Specifier, Construction Specifications Institute, December 7 2018, accessed 2026-09-10
The same technical note states that proper consideration must always be given to moisture control wherever there are openings in masonry walls, and that there must always be a mechanism to channel the flow of water present in the wall to the outside. It specifies that 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. It adds that regardless of whether flashing is used, weepholes should be provided in the facing at the level of the lintel to permit the escape of accumulated moisture.
Source: Brick Industry Association, Technical Notes 31B, Structural Steel Lintels, accessed 2026-09-10
Section R703.8.5 of the Residential Code of New York State requires that flashing be located beneath the first course of masonry above finished ground level above the foundation wall or slab, and at other points of support including structural floors, shelf angles and lintels, where masonry veneers are designed in accordance with Section R703.8. Section R703.4 additionally requires approved corrosion-resistant flashing, applied shingle fashion to prevent water entering the wall cavity or reaching the structural framing, at exterior window and door openings, at the intersection of chimneys or other masonry construction with frame or stucco walls, under and at the ends of masonry, wood or metal copings and sills, at wall and roof intersections and at built-in gutters.
Source: 2020 Residential Code of New York State, Section R703, Exterior Covering, via UpCodes, accessed 2026-09-10
Section R703.8.6 of the Residential Code of New York State requires weepholes in the outside wythe of masonry walls at a maximum spacing of 33 inches on center, not less than three sixteenths of an inch in diameter, located immediately above the flashing. Section R703.8.4.1.1 requires additional metal ties around wall openings greater than 16 inches in either dimension, spaced not more than three feet on center around the perimeter of the opening and placed within 12 inches of it.
Source: 2020 Residential Code of New York State, Section R703, Exterior Covering, via UpCodes, accessed 2026-09-10
The Brick Industry Association's technical note on structural steel lintels states that the steel for lintels should as a minimum comply with ASTM A36, and that steel angle lintels should be at least one quarter of an inch thick with a horizontal leg of at least three and a half inches for use with nominal four inch thick brick. On maintenance it states that for harsh climates and exposures consideration should be given to the use of galvanized steel lintels, and that if this is not done then the steel lintels will require periodic maintenance to avoid corrosion.
Source: Brick Industry Association, Technical Notes 31B, Structural Steel Lintels, accessed 2026-09-10
The Brick Industry Association 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 carried and calculation of the stresses developed. Its serviceability limit is that lintels supporting masonry should be designed so that their deflection does not exceed one six-hundredth of the clear span, and not more than three tenths of an inch, under the combined superimposed live and dead loads.
Source: Brick Industry Association, Technical Notes 31B, Structural Steel Lintels, accessed 2026-09-10
The article states that the effects of corrosion on metal building components range from undesirable appearance to hazardous structural conditions, and that this is particularly the case for masonry buildings constructed in the early 1900s where unprotected structural steel is often in contact with exterior wall construction. It notes that both the masonry and the steel can be affected and that ongoing corrosion of the steel may be concealed within the wall. In masonry buildings, corrosion of steel is typically associated with water that migrates through the exterior cladding and reaches the embedded steel, which can affect beams, columns, lintels and anchorages that form part of the exterior wall assembly.
Source: Deborah Slaton and David S. Patterson, AIA, both of Wiss, Janney, Elstner Associates, Expanding on structural steel, Failures column, The Construction Specifier, Construction Specifications Institute, December 7 2018, accessed 2026-09-10
Ranked instead by the share of housing built between 1940 and 1959, the era in which steel angle lintels over openings became standard in brick and brick-veneer houses, the county orders itself completely differently: Galeville 60.7 percent, Seneca Knolls 58.9, Mattydale 54.6, Westvale 51.3, Lyncourt 47.1, Fairmount 42.7, North Syracuse village 38.5, Geddes town 37.1, Salina town 35.0, Solvay village 31.3, Camillus town 30.4, Liverpool village 27.1, Fayetteville village 26.8, East Syracuse village 26.4, DeWitt town 25.6, the City of Syracuse 23.3, Manlius town 22.3, Cicero town 19.7, Baldwinsville village 17.3, Marcellus town 15.1, Skaneateles village 13.1 and Clay town 12.8.
Source: US Census Bureau, American Community Survey 2020-2024 5-year estimates, table B25034 Year Structure Built and table B25035 Median Year Structure Built, accessed 2026-09-10
Under the 1991 to 2020 climate normals for Syracuse, the daily minimum temperature falls to 32 degrees Fahrenheit or below on 129.5 days of a normal year, but the daily maximum stays below 32 degrees on only 45.7 days. The difference, about 84 days a year, is days on which the temperature crosses freezing in both directions rather than staying below it.
Source: NOAA National Centers for Environmental Information, 1991-2020 US Climate Normals, station USW00014771 Syracuse Hancock International Airport, accessed 2026-09-10
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