Lintel Deflection
A lintel that bends too much can allow the masonry above to settle or rotate, producing cracks at corners or through the units above the opening.
Masonry Openings & Lintels
Cracks Above Windows and Doors
Cracks at the corners of a window or door often look like a simple mortar problem, but openings are some of the most mechanically complicated places in a masonry wall.
The masonry above an opening must be supported. It also has to accommodate building movement and, in many wall systems, drain water that gets behind the outer brick. When a steel lintel rusts, deflects or loses adequate bearing, or when the wall is moving around the opening, cracks can become the first visible clue.
Do not photograph only the crack. Show the entire window or door, the masonry above it, the ends of the lintel where visible, the sill and several feet of wall on each side.
A crack above an opening can be a mortar symptom, a movement problem, a support problem or several of these at once.
What the Pattern Can Suggest
What a Lintel Does
The masonry above a window or door needs a load path around the opening.
A lintel spans across an opening and supports the masonry above it. In many brick walls this is a steel angle or other steel member, although older buildings may use stone, reinforced masonry, arches, wood or other systems.
The lintel needs adequate strength, stiffness and bearing at each end. If it deflects too much, loses section through corrosion or does not bear properly into the surrounding masonry, the courses above can crack or move.
The opening itself also changes the geometry of the wall. Expansion, contraction and settlement often concentrate stresses at the corners because the continuous masonry has been interrupted.
Four things to inspect around an opening
1The crack pattern
2The lintel or arch supporting the masonry
3The water-management details above the opening
4Whether the wall or opening is actually moving
Why Openings Crack
Several different mechanisms can create damage in almost the same location.
The surrounding signs help separate corrosion, deflection, movement and moisture problems.
Steel Corrosion
Rust expansion can push upward and outward against surrounding masonry, opening joints, cracking brick and displacing courses near the lintel.
Inadequate Bearing
If the lintel does not have adequate support at its ends, concentrated stresses can damage the masonry where the support transfers into the wall.
Wall Movement
Thermal, moisture and structural movement can concentrate at window and door corners even when the lintel itself remains sound.
Water Entry
Failed flashing, sealant or drainage can keep the lintel and nearby masonry wet, contributing to corrosion, staining and freeze-thaw deterioration.
Settlement or Structural Movement
Movement elsewhere in the building can use the opening as a stress concentration point, creating diagonal or stepped cracking from its corners.
Corner cracks are common clues. Their direction, whether they follow joints or break brick, and whether the courses above are displaced all help narrow the investigation.
Cracks From Window Corners
The corner is where changes in support and wall geometry meet.
A diagonal or stair-step crack from the corner of an opening can be associated with differential settlement, building movement, expansion and contraction, or movement of the support above the opening.
Brick Industry Association guidance on masonry movement specifically notes that openings can concentrate stresses when brick expansion and other building movements are restrained.
The crack direction is useful, but it does not identify the cause by itself. Look for rust, sagging, displaced courses, previous patching and movement elsewhere in the wall.
Compare masonry crack patterns →Steel Lintel Corrosion
Rust can create enough expansion to push the masonry apart.
Steel does not simply become thinner when it corrodes. The corrosion products occupy more volume than the original metal. When that happens inside or directly beneath masonry, expansion can force against the surrounding brick and mortar.
Typical clues include rust staining, horizontal cracking near the lintel, lifted brick courses, cracked units, open joints and local outward displacement.
Corrosion also reduces the remaining steel section. A lintel can therefore have two related problems at once: rust expansion damaging the masonry and loss of steel capacity or stiffness.
The repair depends on how much corrosion has occurred, whether the lintel is still structurally adequate and whether the source of repeated wetting can be corrected.
Rust staining is evidence, not the whole diagnosis. The important questions are how much steel has deteriorated, whether the lintel has moved and whether the masonry above has lost support or alignment.
What the Pattern Can Suggest
Read the crack together with the lintel and the courses around it.
These are inspection clues, not automatic diagnoses.
Diagonal Crack From One Corner
Can point toward localized movement, settlement or stress concentration at the opening. Check whether the rest of the wall shows related movement.
Cracks From Both Upper Corners
May raise questions about support, lintel deflection, expansion restraint or movement of the masonry directly above the opening.
Horizontal Crack Along the Lintel
Corrosion, differential movement or separation along the support line should be considered, especially if rust staining or displacement is visible.
Brick Lifted Above the Opening
Upward displacement can be consistent with expanding corrosion beneath the masonry, although the steel condition must be inspected to confirm the cause.
Sagging or Dropped Courses
Downward movement may indicate lintel deflection, inadequate bearing or loss of support and deserves closer structural assessment.
Cracks Through the Brick
Through-unit cracking suggests the stress was not relieved by mortar joints alone and makes support and structural movement more important to investigate.
Bearing Matters
The lintel does not only have to span the opening. Its ends need proper support.
Loads from the masonry above must transfer through the lintel and into the wall at each end. If the bearing area is inadequate, deteriorated or disturbed by previous alterations, stresses can become concentrated in a small area of masonry.
Canadian building-code intent documents specifically identify inadequate lintel size, excessive span and inadequate bearing as conditions that can lead to cracking or structural failure of masonry veneer above openings.
On an existing building, the important visual clues are cracked bearing zones, crushed or displaced brick, sagging, altered openings and repairs that may have changed how the load is carried.
Look at both ends of the opening
✓Is the lintel visibly bearing into sound masonry?
✓Are bricks at the ends cracked or displaced?
✓Has the opening been widened or altered?
✓Do cracks begin at only one end or both?
Corrosion needs moisture. If steel is rusting, ask how water is reaching it and whether the repair restores drainage as well as replacing or treating the metal.
Flashing, Weeps & Water
In brick veneer, the opening also has to manage water behind the brick.
Brick veneer is a drained wall system. Some rain can pass through the outer masonry, which is why concealed flashing and drainage paths are used to direct water back to the exterior.
At windows and doors, flashing above the opening, end conditions, weeps and perimeter transitions help prevent water from collecting around the lintel and entering the wall assembly.
When those details are missing, blocked or failed, the lintel can remain wet and corrosion can accelerate. Water may also show up as staining, efflorescence, interior leakage or freeze-thaw deterioration around the opening.
The exact wall detail varies with age and construction type. Older solid masonry walls do not necessarily contain the same cavity flashing details as modern brick veneer.
Read the brick veneer anatomy guide →Why Repointing Alone Often Fails
If the lintel is still moving, the crack will keep asking to reopen.
Filling cracked joints can improve appearance and weather resistance after the underlying problem has been corrected. It does not stop an actively corroding lintel from expanding or a deflecting support from continuing to move.
Repeated mortar patches directly above windows and doors are therefore useful evidence. They can indicate that earlier repairs addressed the visible crack without changing the condition that created it.
A durable repair may involve removing masonry to expose the lintel, evaluating the steel, replacing or repairing the support as appropriate, restoring flashing and drainage, and then rebuilding the masonry with compatible materials.
Previous patching tells a story. If the same crack repeatedly returns, the repair history should be part of the diagnosis rather than simply adding another layer of mortar.
Repairing a Corroded Lintel
The correct scope depends on the steel condition and the masonry it supports.
Light surface corrosion on an otherwise sound and properly supported lintel is a different condition from deep section loss, heavy scaling, distortion or sagging.
Where the lintel is no longer serviceable, replacement may require temporary support of the masonry, selective dismantling above the opening, installation of a properly designed support, restoration of water-management details and rebuilding the brickwork.
Where structural design is required, the lintel should not be selected by a simple rule of thumb. Brick Industry Association guidance specifically treats structural steel lintels as engineered support elements for brick masonry.
The final repair method depends on wall type, opening width, loads, existing bearing, corrosion and local building requirements.
A lintel repair may involve
1Temporary masonry support
2Selective brick removal
3Steel assessment, treatment or replacement
4Correct bearing and support
5Flashing and drainage restoration where applicable
6Brick and mortar matching during rebuild
Loose units change the urgency. If cracking around an opening has produced displaced or unstable brick, keep people away from the fall zone and arrange prompt assessment.
When to Escalate
Cracking becomes more important when support, displacement or falling masonry is involved.
!The lintel is visibly sagging or distorted
!Brick courses above the opening are dropping or lifting
!Several units are loose or displaced
!The opening itself is visibly racked or distorted
!Cracks reopen quickly after previous repair
!There is uncertainty about bearing, structural support or a modified opening
Some conditions are primarily masonry repair. Others need engineering input to define the support requirement before the wall is rebuilt.
Atlantic Canada Context
Repeated wetting and winter exposure can turn a small lintel problem into a masonry problem.
Across Prince Edward Island, Nova Scotia and New Brunswick, exposed openings can experience wind-driven rain, wet snow, freeze-thaw cycling and long periods of seasonal moisture.
Water reaching steel accelerates corrosion. Water reaching cracked brick and open joints can then contribute to freeze-thaw deterioration around the same opening. The result can be a combined corrosion, movement and masonry-damage problem rather than one isolated defect.
That is why the repair should restore both support and water management where either has failed.
Regional lesson: A crack can create a water path, and the water can then accelerate deterioration. Movement and moisture often reinforce each other over repeated winters.
What to Photograph
Give the opening enough context to show support, movement and water details.
Whole Opening
Show the entire window or door plus several courses above and masonry on both sides.
Both Lintel Ends
Photograph where the support bears into the wall and any cracks beginning at those areas.
Rust & Steel
Capture rust staining, visible scaling, distortion or separation where the lintel can be seen.
Crack Close-Up
Show whether the crack follows joints, crosses bricks and has displacement across its face.
Water Details
Include sills, sealant interfaces, weeps, overhangs and other nearby drainage conditions.
Interior Clues
If present, photograph interior staining, distorted trim or cracking aligned with the exterior opening.
Technical References
Why support, corrosion and movement all belong in the diagnosis.
National Park Service guidance identifies cracking and displacement around openings as common signs of deflecting or failed lintels and arches. It also notes that iron and steel lintels can create cracking as they deflect or rust.
Brick Industry Association Technical Note 31B treats structural steel lintels as critical support elements whose loads, stresses and serviceability should be properly designed rather than selected by rule of thumb.
Canadian National Building Code intent statements identify excessive lintel deflection and inadequate bearing as conditions that can lead to cracking or structural failure of masonry veneer over openings.
Brick Industry Association movement guidance also explains how temperature, moisture and restraint can concentrate cracks around windows and doors even when the immediate support is not the only cause.
National Park Service: Common Problems with Brick Masonry →
Brick Industry Association: Technical Notes, including 31B Structural Steel Lintels →
NRC / National Building Code Intent: Masonry Lintels & Bearing →
Brick Industry Association Technical Note 18: Volume Changes & Movement →
About the Author
Prepared by Dean MacArthur, DinoMac Masonry Ltd.
Dean is a third-generation mason with more than 20 years of hands-on experience working with brick, natural stone, chimneys, foundations, repointing and masonry restoration in Prince Edward Island.
The DinoMac Masonry Knowledge Centre uses PEI field experience to explain masonry conditions that are also common across Atlantic Canada and other cold, wet climates.
Last reviewed: August 26, 2026
Lintel & Opening Crack FAQ
Common homeowner questions.
Why do bricks crack above windows and doors?
The cause may be lintel deflection, corrosion, inadequate bearing, wall movement, settlement, moisture or a combination.
How does lintel rust crack brickwork?
Corrosion products expand around the steel and can push against the surrounding masonry, opening joints and displacing brick.
Does rust staining mean the lintel has failed?
Not automatically. The steel condition, section loss, deflection, bearing and masonry displacement determine the repair scope.
Can repointing fix the crack?
Only after the cause is stable. Repointing will not stop an actively corroding or deflecting lintel from moving.
Does brick veneer need flashing over openings?
Drainage-type veneer generally relies on flashing and drainage details to redirect water, although exact construction varies by age and wall type.
When should an engineer look at it?
When there is significant sagging, displacement, uncertain support or bearing, major through-unit cracking or repeated movement after repair.
Related Knowledge Centre Guides
Continue from the crack into the wall, water-management or support system behind it.
Cracking Above a Window or Door in PEI?
Send the whole opening, both ends of the lintel and the crack pattern.
Include wide and close photos, rust staining or visible steel, any sagging or displacement, nearby water-management details and the PEI property location. DinoMac can assess whether the visible problem appears primarily masonry-related or whether the support should also receive structural review.