The Complete Guide to Structural Cracks, Building Movement, Inspection Costs and When to Engage a Structural Engineer
Sheer Force Engineering · Structural engineers for existing buildings · Melbourne
Examples of cracking encountered during structural inspections. The location, direction, width and pattern of a crack often provide valuable clues about what is causing it.
If a wall is leaning, cracks are rapidly worsening, doors or windows are becoming difficult to operate, or you have concerns about structural safety, we recommend obtaining professional advice as soon as possible.
Need help understanding whether a crack is serious?
Otherwise, continue reading to learn what causes cracks, when they matter and what a structural engineer looks for during a crack inspection.
Looking for a quick answer?
Start with the four questions we are asked most frequently about structural cracks, inspections and building movement.
$850 – $10,000+
Typically, depending on complexity, building size, access and reporting requirements.
Read moreNo
Many cracks are caused by moisture, mortar deterioration, brick growth, structural alterations or corrosion.
Read moreSometimes
Some cracks are cosmetic. Others require investigation. Width, direction and progression separate the two.
Read moreNot Always
Many inspections begin with verbal advice, with written reporting added only where it is genuinely needed.
Read moreContents
01
If you've arrived on this page, there's a good chance you've noticed cracking in your building and you're wondering what it means.
Cracking in a brick wall
Stair-step cracking in masonry
Cracks in plasterboard
Cracks in a concrete slab
Cracking around windows and doors
Cracks near footings
Doors and windows becoming difficult to operate
Signs that part of the building may be movingThe first thing to know is that not all cracks are a cause for concern.
Some are cosmetic.
Others can indicate movement, deterioration or structural issues that warrant further investigation.
The purpose of a crack inspection is not simply to measure the crack.
The purpose is to understand why it has occurred and whether any action is required.
One of the most common mistakes we see is spending money repairing a crack before understanding what caused it.
A crack caused by deteriorated mortar requires a very different solution to a crack caused by footing movement.
That's why diagnosis comes first.
Many cracks are cosmetic.
Others may indicate movement, deterioration or loss of structural integrity.
Understanding the difference is the first step.
02
Not every crack is serious.
However some crack types warrant further investigation. Our earlier article on how you can tell if a crack is structural sets out the crack widths engineers use as a starting point.
Most of the time, the question is not how wide a crack is today.
The question is whether the crack is changing, and whether anything else in the building is moving with it.
One of the most useful things a building owner can do is photograph a crack with a ruler or coin beside it.
Record the date and repeat the photograph several months later.
A crack that has remained stable behaves very differently from one that is actively growing.
In many cases, the change in a crack is more important than the crack itself.
Cracks wider than 5 mm
Once a crack passes roughly 5 mm it is worth measuring and recording rather than filling, because width at this scale usually reflects real movement somewhere.
Cracks are growing
A crack that is longer, wider or newly branching compared with your earlier photographs tells us the cause is still active.
New cracking appears suddenly
Cracking that appears over days or weeks, rather than gradually over years, points to a recent change such as a leak, a load change or ground movement.
Cracking is associated with water damage
Damp staining, efflorescence or blistered paint alongside a crack often means water is driving deterioration behind the surface.
Walls appear to be leaning
Out-of-plumb masonry is a stability question, not a finish defect, and it should be assessed rather than monitored.
Doors or windows are sticking
Frames that have racked out of square suggest the structure around them has distorted, not just the finishes.
Brickwork is bulging
Bulging or bowing brickwork can indicate loss of restraint, corroded wall ties or lateral pressure on the wall.
Cracking has appeared following nearby construction works
Excavation, piling, vibration or dewatering next door can change ground support. Early records matter for both safety and liability.
As a general rule, a stable crack that has not changed for years is often less concerning than a crack that is actively growing.
Movement frequently matters more than crack width.
Understanding what causes cracking is often the first step toward determining whether action is required.
In the next section we explore the different crack types we commonly encounter and what they can tell us about a building.
Visual Severity Guide
This guide is a starting point, not a diagnosis. It reflects how we prioritise attention when we first walk a building, and every band assumes the crack is read alongside building movement, drainage and history.
Fine hairline cracking in paint, plaster or render finishes. Typically stable, seasonal, and addressed through ordinary maintenance.
Minor cracking that reappears after repair, or small masonry cracks that may reflect seasonal movement. Record widths and dates before spending money.
Patterns that indicate relative movement between parts of the building. Worth an engineer's assessment before any repair is specified.
Leaning, bulging or displaced masonry, rapidly widening cracks, or any sign that an element is losing the ability to carry load. Seek advice immediately.
Important
No crack should be assessed in isolation. Crack width, location, movement, building type, age, moisture exposure and building history all influence the level of concern. Where significant movement, distortion or ongoing cracking is present, professional assessment is recommended.
03
Paint cracking. Paint films are thin and brittle compared with the substrate beneath them. Repeated cycles of heat, cold and humidity crack the film long before anything structural is affected. Paint cracking that does not continue into the plaster or masonry behind it is a decorating matter.
Plaster shrinkage. Plaster and plasterboard sets shrink as they dry and continue to move seasonally with the timber framing around them. Fine cracks at cornices, wall junctions and above openings are extremely common in Melbourne homes, particularly in the first few years after new work.
Minor settlement. Almost every building settles a little as it takes up its own weight and the soil beneath it adjusts. Where that settlement is small and even, the resulting hairline cracking stabilises and does not progress.
Surface rendering cracks. Render and stucco are applied coatings with different stiffness and shrinkage characteristics to the wall behind. Map cracking, crazing and fine linear cracks in render are usually confined to the coating, though render can also conceal significant masonry defects, so it is worth confirming what lies behind it.
Cosmetic cracking can often remain stable for years. Not every crack requires engineering intervention. The practical test is whether the crack is changing, and whether it is accompanied by any distortion of the building itself.
Most cosmetic cracks remain stable for many years and can often be repaired as part of routine maintenance.
However, any crack that is actively changing, widening or becoming associated with other symptoms should be reassessed.
The distinction is often not whether a crack exists, but whether it is continuing to move.
04
Stair-step cracking. A crack that steps diagonally through mortar joints means the wall has parted along its weakest path. It usually reflects differential movement, mortar deterioration, or both acting together.
Diagonal cracking. Diagonal cracks from the corners of openings indicate distortion. Openings are the weak points in a wall, so they are where movement declares itself first.
Horizontal cracking. Horizontal cracks along bed joints can indicate lateral load, corroding wall ties or lintels, brick growth against a rigid restraint, or loss of restraint at the top of a wall. They deserve prompt attention.
Leaning walls. A wall out of plumb has already moved. The question becomes whether it is still moving, and whether the wall retains adequate stability and restraint in its current position.
Bulging masonry. Bulging often indicates that a wall has begun to separate through its thickness, that ties have corroded, or that a solid wall is delaminating. It is a stability issue rather than an appearance issue.
Cracks associated with movement. Cracking that appears with sticking doors, sloping floors, gaps opening at skirtings or cornices, or masonry displaced out of line is evidence that the structure itself has changed shape.
Engineers rarely assess cracking in isolation.
Crack width, location, direction, associated movement, moisture exposure and building history all contribute to the diagnosis.
Two cracks that appear visually similar can have completely different causes and require very different solutions.
This is why professional assessment focuses on the overall pattern of symptoms rather than any individual crack.
Many building owners struggle to determine whether cracking is cosmetic or evidence of a more significant issue.
A structural engineer can often identify the likely cause and provide practical advice on the next steps.
05
Buildings crack because something has moved, expanded, contracted, corroded or lost strength. In Melbourne, eight causes account for the overwhelming majority of the cracking we are asked to investigate — and more than one is usually at work. Concrete behaves differently again, and we cover that in detail in why concrete slabs crack.
Uniform settlement rarely damages a building, because the whole structure moves together. Damage comes from differential movement, where one part settles more than another and the structure is forced to distort.
Melbourne's reactive clay soils shrink in dry weather and swell when wet, so footings can rise and fall seasonally. Older shallow footings, extensions built on different footing systems, and poorly drained sites are the usual candidates.
Differential movement
Water is the single most destructive influence on an existing building. It erodes lime mortar, softens masonry, corrodes wall ties and reinforcement, rots timber and changes the volume of soil beneath footings.
Leaking plumbing, blocked or disconnected stormwater, failed flashings, poor site falls and failed waterproofing regularly sit behind cracking that first appears to be structural.
Material weakening
Fired clay bricks slowly reabsorb moisture after manufacture and permanently expand over decades. The movement is small per metre but significant across a long wall.
Where articulation joints are absent — as in most older masonry — that expansion has nowhere to go, and it appears as vertical cracking at corners and junctions, or horizontal cracking where the wall pushes against a rigid element.
Long-term expansion
In solid masonry, the mortar transfers load between bricks and holds the wall together as a single element. When lime mortar washes out or turns to sand, the wall loses its integrity from within.
This is one of the most commonly missed causes of heritage cracking. We have investigated buildings underpinned repeatedly where the real problem was mortar loss hidden behind render.
Loss of wall integrity
Steel expands as it rusts, occupying several times its original volume. Embedded lintels, wall ties, reinforcement and structural steelwork therefore split the material around them as they corrode.
The tell-tale signs are cracking that follows a straight line above an opening, rust staining, spalling concrete or displaced brick courses. Corrosion damage is progressive and does not stabilise on its own.
Expansive rusting steel
Removing a wall, opening up a kitchen, taking out a chimney or adding a level changes where load travels. If the new path is inadequate or the supporting elements deflect, cracking follows.
Alteration-related cracking often appears within months of the work, close to new beams or removed walls, and can usually be traced by comparing the current structure with the original arrangement.
Changed load paths
Large trees draw significant volumes of moisture from the soil, and on reactive clay that drying causes localised shrinkage and settlement of nearby footings.
Removing a mature tree can produce the reverse effect, with the soil rehydrating and heaving over several years. Tree influence is real, but it is also frequently blamed when other causes dominate.
Soil moisture change
Excavation beside an existing building removes lateral support, lowers groundwater and can allow adjacent soil to move. Piling, rock breaking and heavy plant add vibration.
Cracking that appears suddenly while neighbouring works are underway should be documented immediately, ideally against a pre-construction dilapidation record.
Excavation and vibration
06
Every crack type below carries a typical level of concern, but the level shifts with width, progression and what else the building is doing. Use it to understand what you are looking at, not to rule a crack out.
Cracking that steps diagonally through the mortar joints, following the weakest path through the wall. It is one of the clearest signals that part of a wall has moved relative to the rest of it.
Likely causes
Cracks running up and down a wall, frequently at junctions, corners or long unarticulated runs of brickwork. Width, taper and whether the crack passes through bricks or joints tell you a great deal.
Likely causes
Cracks running at roughly 45 degrees, commonly from the corners of windows and doors. Openings concentrate stress, so diagonal cracks often reveal the direction a building is moving.
Likely causes
Cracking along a bed joint, sometimes with the wall above displaced sideways. Horizontal cracks can indicate lateral pressure, corrosion of embedded metal, or loss of restraint at the top of a wall.
Likely causes
Concrete cracks for many reasons, and only some of them matter structurally. Pattern, timing, width and whether reinforcement is exposed separate a curing artefact from a durability problem.
Likely causes
Solid brick heritage walls carry load through the masonry itself, so lime mortar loss, damp and past alterations matter more than in modern construction. Heritage cracking is frequently misread as footing failure.
Likely causes
Most ceiling cracks are plaster and cornice movement caused by seasonal timber shrinkage. Cracks that follow a joist line, sag, or coincide with wall cracking deserve a closer look.
Likely causes
Balconies are exposed, thin and frequently the first element where water reaches reinforcement. Cracking along the slab edge or soffit is a durability and safety matter, not a finish defect.
Likely causes
Cracking in slabs, footings or basement walls needs to be read against the soil, drainage and footing type. The crack is a symptom; the ground conditions usually hold the explanation.
Likely causes
Crack width is only one part of the assessment process, however it can provide a useful starting point when deciding whether monitoring or further investigation is appropriate.
| Approximate crack width | General guidance |
|---|---|
| Hairline (< 0.5 mm) | Usually monitor and record. Common in plaster, paint and render finishes. |
| 0.5 mm - 1 mm | Monitor for change. Photograph and record location. |
| 1 mm - 5 mm | Consider engineering advice depending on location, progression and building type. |
| Greater than 5 mm | Investigation is generally recommended. |
| Rapidly changing crack (any width) | Seek professional assessment promptly. |
Important
Crack width alone does not determine severity. Location, crack pattern, building type, movement history, moisture exposure and the presence of other symptoms are often just as important as the width of the crack itself. Two cracks of the same width can have very different causes and require very different responses.
07
We start with a conversation. When did the cracking appear, is it changing, what work has been done to the building, and what outcome do you actually need? This often shapes the scope before anyone attends site.
An engineer attends and walks the building inside and out, including subfloor, roof space and external ground levels where accessible. Drainage, ground falls, vegetation and neighbouring works are all part of the picture.
Each significant crack is located, measured, photographed and described by direction, taper and whether it passes through units or joints. Crack widths are recorded against a gauge so future readings are comparable.
We check wall plumbness, floor levels, distortion of openings, the load path and any evidence of past alterations. The pattern across the whole building usually reveals the cause more clearly than any single crack.
Where the cause remains uncertain, targeted investigation follows: removing render or linings at selected points, mortar assessment, moisture readings, drainage testing, footing exposure, survey levels or crack monitoring over time.
You receive a plain explanation of what is causing the cracking, how serious it is, and what should be done — including where the appropriate answer is to monitor and do nothing further for now.
If you need documentation for a builder, an owners corporation, an insurer, a purchaser or a dispute, we prepare a written report. Many inspections conclude with verbal advice alone.
08
Localised Inspection
A single crack or one area of concern, with straightforward access.
$850 + GST
Typical client
Homeowners
Residential Inspection and Written Summary
A house or unit where you need something in writing to act on.
$850 – $2,000 + GST
Typical client
Homeowners, property buyers and vendor reports
Detailed Residential Investigation
Widespread cracking, multiple causes, or a dispute over the diagnosis.
$2,000 – $5,000+
Typical client
Properties with widespread cracking, multiple defects or disputes about the cause
Commercial Crack Investigation
Apartment buildings, heritage assets, commercial and industrial sites.
$5,000 – $10,000+
Typical client
Owners corporations, commercial buildings and heritage assets
Forensic Structural Investigation
Matters heading toward insurance, litigation or expert evidence.
$10,000+
Typical client
Complex structural issues, expert reports and major deterioration investigations
Every project is different. Fees vary depending on building size, complexity, access and reporting requirements.
09
No.
One of the most common misconceptions is that cracking automatically means the footings have failed.
In reality, cracking can be caused by:
Historic lime mortars often weaken long before the surrounding brickwork.
Leaks, poor drainage and changes in moisture conditions can all contribute to cracking.
Removing walls, enlarging openings and structural alterations can change load paths.
Clay bricks slowly expand over time and can generate significant cracking.
Expanding rusting steel can crack both masonry and concrete.
Additional loads sometimes create localised cracking without any footing movement.
Engineering Insight
Underpinning is expensive, disruptive and, when applied to the wrong problem, entirely ineffective.
Where footing movement genuinely is the cause, underpinning may be exactly the right solution.
However, the diagnosis should follow evidence, not precede it.
Many building owners are surprised to discover that cracking is often caused by issues such as mortar deterioration, moisture changes, brick growth, corrosion or building alterations rather than footing failure alone.
10
Three investigations where the obvious explanation for cracking turned out to be the wrong one.
A heritage Melbourne house had been underpinned multiple times over decades yet continued to move. Investigation revealed severe mortar deterioration hidden behind render.
Read the investigation →A heritage masonry building displayed significant cracking that initially appeared to be footing-related. The investigation revealed differential brick growth and moisture-related expansion.
Read the investigation →A balcony waterproofing project uncovered significant structural deficiencies and eventually evolved into a detailed forensic engineering investigation.
Read the investigation →11
Whether you're concerned about a heritage property, residential home, apartment building or commercial asset, understanding the cause of cracking is often the first step toward an effective solution.
