Cracking is one of the most common concerns homeowners raise about a new build in Australia - and one of the most misunderstood. Some cracks are routine settlement that any new house will show. Others are early warning signs of a structural defect that needs to be investigated, recorded and rectified before it gets worse.
Knowing the difference matters. Treating a structural crack as cosmetic can leave a serious defect to develop unaddressed while contractual and statutory claim periods run. Treating a cosmetic crack as a structural defect creates unnecessary friction with the builder and can lead a homeowner to focus on the wrong issues during handover.
This guide explains the common types of cracking in Australian new builds, why they appear, when they signal a defect, what to do when you find one and who is responsible for putting it right. For the broader residential construction context, refer to the BUILTLY complete guide to building a house in Australia.
What is cracking in new builds?
Cracking refers to any visible fracture in the materials of a new building - plasterboard walls and ceilings, cornices, masonry, render, concrete slabs, brick veneer, tiling and external paving. In a new build, cracks generally fall into one of three categories: shrinkage cracks as materials cure and dry, settlement cracks as the building responds to its first seasonal cycle, and movement cracks driven by soil, footing or structural causes that point to a deeper issue.
Cracking is assessed against the National Construction Code, the relevant Australian Standards and industry tolerance documents such as the Guide to Standards and Tolerances. These documents set out what is considered acceptable workmanship and what counts as a defect that the builder must rectify.
Cracking is not, on its own, a verdict. It is an observation. The next step is identifying the type of crack, its likely cause and whether it sits inside or outside the acceptable tolerances for the element it appears in.
Why cracks happen
Cracks in a new build can have a single cause or several causes acting together. The most common drivers in Australian residential construction are:
Shrinkage and curing
Concrete, render, mortar, plaster and timber all change dimension as they dry and cure. The result is a network of fine hairline cracks that typically appear in the first few months at cornice junctions, plasterboard joints and the corners of openings.
Settlement
As the structure beds onto its footings and the framing takes its full load, small differential movements occur. These produce thin cracks at the junctions of different materials and at points of natural weakness such as the corners of door and window openings.
Reactive soil movement
Many Australian sites have reactive clay soils that expand when wet and shrink when dry. If the footing system has not been designed for the site classification - or if site drainage allows moisture to concentrate at one side of the slab - the slab and the walls above it can move, producing diagonal cracks. For background on how soils are assessed, refer to the BUILTLY guides on soil classification in Australia and how to read a soil report in residential construction.
Inadequate footing design or construction
Footings that are undersized for the soil class, poorly reinforced or constructed on inadequately prepared ground will not restrain the building from movement. The cracks that follow are typically wider, diagonal and progressive rather than fine and stable.
Workmanship
Poorly mixed mortar, missing control joints in long masonry runs, plasterboard joints that have not been set correctly and tiles laid without adequate movement allowance all produce cracking that has nothing to do with the structure itself and everything to do with how the work was carried out. The companion guide to expansion and articulation joints in Australia explains how planned joints manage movement before uncontrolled cracks form.
External factors after handover
Large trees planted near footings, blocked or redirected stormwater, leaking pipes under or beside the slab and significant landscaping changes can all introduce movement that did not exist at handover. These can produce the same visible symptoms; whether the builder is responsible depends on the cause.
Types of cracks in a new build
Not all cracks look or behave the same way. Identifying the type of crack is the first step in understanding what is causing it.
Hairline cracks
Very fine cracks under approximately 0.1mm wide, typically in plaster, paint and cornice junctions. Almost always cosmetic. They are usually filled at the end of the defects liability period when settlement has stabilised.
Shrinkage cracks
Short, narrow cracks that follow plasterboard joints, the edges of openings or the line of a control joint. They are a normal consequence of materials drying out and rarely indicate a structural issue.
Vertical cracks
Cracks that run vertically through plasterboard, masonry or render. Narrow vertical cracks at a junction or opening are usually movement-related and not structural. Wider vertical cracks that pass through bricks rather than along mortar joints are more significant and warrant inspection.
Diagonal or stepped cracks
Diagonal cracks in walls, or stepped cracks that follow mortar joints in brickwork, are typically caused by differential settlement or soil movement. These are the cracks that most often signal a footing or soil-related defect and should be assessed by a structural engineer if they are wider than about 1mm in masonry.
Slab and floor cracks
Fine shrinkage cracks in a concrete slab are common and usually cosmetic. Cracks wider than about 1mm, cracks that telegraph through floor tiles or timber flooring, or cracks accompanied by unevenness in the floor are more serious and need investigation.
External render and brickwork cracks
External cracks in render and brickwork are exposed to weather and can let water into the wall cavity. Even relatively narrow external cracks should be raised with the builder because the consequences of leaving them unaddressed go beyond appearance.
When cracks typically appear
Most cracking in a new build follows a recognisable timeline. The first wave of shrinkage and settlement cracking generally appears in the first 3 to 6 months after practical completion as materials dry out and the building takes its full load.
A second wave often appears in the first 12 to 18 months as the building experiences its first full seasonal cycle - a hot summer, a wet winter, or the first significant change in soil moisture around the slab. This is when reactive-soil movement is most likely to make itself visible.
Cracking that appears suddenly years after handover, or cracking that grows steadily over weeks and months, is not normal settlement. It points to an ongoing cause - usually moisture, soil movement, tree roots or footing inadequacy - and warrants an immediate inspection rather than a wait-and-see approach.
When to worry: warning signs
Warning - investigate without delay
Cracks wider than about 1mm in masonry
Masonry cracks at or above this width, particularly when stepped or diagonal, point to differential movement and need a structural opinion.
Cracks that are widening over time
Any crack that is visibly longer or wider than it was a few weeks ago is a sign of an active cause that has not been arrested.
Diagonal cracks through openings
Diagonal cracks running from the corners of doors or windows are a classic signal of footing or soil-related movement.
Cracks accompanied by other symptoms
Doors that bind or swing open on their own, windows that no longer close cleanly, gaps opening between skirting and floor, or visibly sloping floors all suggest the cracking is one symptom of a wider movement issue.
Cracks in structural elements
Cracks in load-bearing walls, columns, lintels, slabs or beams are not to be treated as cosmetic regardless of width. They warrant an engineer's assessment.
External cracks letting water in
Any external crack that is allowing water into the wall cavity, or showing visible staining around it, needs to be raised promptly to avoid secondary damage.
Cosmetic cracks: when not to worry
Many cracks in a new build are cosmetic. They are part of the normal behaviour of materials and the structure, and they will be addressed routinely at the end of the defects liability period.
Typical cosmetic cracks
- Hairline cracks at the junction of walls and cornices
- Fine cracks running along plasterboard joints
- Small cracks at the corners of doors and windows in plasterboard
- Hairline shrinkage cracks in concrete slabs and driveways
- Fine cracks at the junction of different materials, such as where plaster meets brick
- Hairline cracks in mortar that do not pass through bricks
These cracks are usually recorded during the defects liability period inspection and rectified in a single rectification visit once settlement has stabilised. Even so, notify the builder in writing promptly so claim deadlines are protected, even if the repair is scheduled later.
What to do when cracks appear
The process for responding to cracking in a new build follows the same steps regardless of severity. The difference is the urgency with which you move through them.
Record it
Photograph each crack with a ruler or coin as a scale reference. Record the date, the room, the element and any related symptoms. Mark the ends of the crack with a pencil so future photographs can show whether it has lengthened.
Raise it in writing with the builder
Email is the appropriate channel. Verbal reports are easily disputed later. Include the photographs, the date the crack was first observed and a request for the builder to inspect.
Allow the builder to inspect
Most builders will inspect cracking promptly within the defects liability period. The inspection should result in a written response identifying whether the crack is considered cosmetic or a defect, and what action will be taken.
Get an independent opinion if needed
If the cracking is significant or the builder's response does not address the cause, engage an independent structural engineer or building inspector. Their report is the evidence that supports any escalation.
Issue a defect rectification notice
Where the builder accepts a defect but does not act, a formal defect rectification notice puts the request on a written footing and starts the clock for escalation. For the structure of such a notice, refer to the BUILTLY guide on defect rectification notices in Australia.
Escalate if necessary
If the builder refuses to rectify a confirmed defect, the next steps are the state building regulator, the home warranty insurer and ultimately the relevant state tribunal. A clear written record from the first observation onwards is the foundation of any successful escalation.
Common mistakes to avoid
Warning - common mistakes
Filling cracks before the cause is identified
Patching and painting over a crack does not address the underlying cause. If the cause is still active the crack will reappear, often wider, and the rectification record becomes harder to follow.
Treating every crack as a structural defect
Raising every hairline crack as a major issue exhausts the relationship with the builder and dilutes attention from the cracks that genuinely matter. Distinguish between cosmetic and structural before escalating.
Relying on verbal commitments
Conversations on site about rectification timing or scope are easily forgotten or disputed. Every commitment should be confirmed in writing on the same day.
Waiting until the end of the defects liability period
Holding all cracking observations until the final defects list can mean an active cause is left undiagnosed for months. Raise structural-looking cracks as soon as they appear, even if cosmetic cracks are batched at the end.
Not photographing with scale and date
Photographs without a scale reference or a date stamp are weak evidence. A ruler, coin or known object next to the crack and a clear date are essential if the matter is ever disputed.
Who is responsible
Responsibility for cracking depends on the cause. Where the cracking is the result of defective work, inadequate footing design, poor ground preparation, missing control joints, substandard mortar or workmanship below the required standard, the builder is responsible. This applies during the defects liability period and the statutory warranty period, which run at the same time.
Where the cracking is the result of homeowner actions after handover - large trees planted close to footings, significant landscaping that changes drainage, modifications that have introduced new loads or moisture sources - the responsibility may shift. Independent expert evidence is often required to attribute the cause correctly.
In disputed cases, the question becomes evidential rather than conceptual. A clearly recorded sequence of photographs, dates, builder correspondence and independent reports is what settles the question in favour of one party or the other.
BUILTLY and cracking evidence
BUILTLY is building a record of completed Australian homes that credits the builder, designers and trades behind each one.
A record kept this way is what an engineer, insurer, regulator or tribunal can actually rely on. For the broader residential construction context that this fits into, refer to the BUILTLY complete guide to building a house in Australia.
Frequently asked questions
Is cracking in a new build in Australia normal?
Some cracking is normal in the first 12 to 24 months of a new build. As materials dry, settle and respond to seasonal movement, fine hairline cracks at cornice junctions, around window and door reveals and along plasterboard joints are common and rarely structural. What is not normal is cracking that is wide, progressive, diagonal across structural elements or accompanied by other signs of movement such as sticking doors, sloping floors or visible separation between elements.
What crack width is considered a defect in an Australian new build?
Industry guidance commonly refers to crack-width categories from negligible (hairline, under 0.1mm) through to severe (over 15mm). Cracks under about 1mm in plasterboard or cornice joints are generally cosmetic and within normal settlement. Cracks over 1mm in masonry, over 2mm in plasterboard, or any crack that is widening, diagonal or accompanied by structural symptoms should be inspected. The Guide to Standards and Tolerances and your state's building regulator publish more specific thresholds.
Who pays to fix cracking in a new build in Australia?
If the cracking is the result of defective work, inadequate footing design, poor ground preparation or workmanship that does not meet the National Construction Code and relevant standards, the builder may be liable under the contract and under statutory warranties, which run at the same time; claim deadlines vary by state. If the cracking is caused by homeowner actions after handover - for example planting large trees near footings or failing to maintain site drainage - responsibility may shift. The cause must be identified before responsibility is assigned.
When do cracks in a new house in Australia typically appear?
Most settlement and shrinkage cracking appears within the first 6 to 18 months after practical completion, as concrete cures, timber dries and the structure responds to its first full seasonal cycle. Reactive-soil movement cracking can appear later, often in the first dry or wet season after handover. Cracks that appear suddenly years after handover, or that continue to widen over months, warrant immediate investigation rather than being treated as routine settlement.
Should I get an independent engineer to assess cracking before I raise it with my builder?
For fine cosmetic cracking, raising it through the standard defects process is usually sufficient. For wider cracks, diagonal cracks, cracks in masonry, cracks accompanied by other movement symptoms or any cracking the builder has dismissed without investigation, an independent structural engineer's report is valuable. It documents the condition, identifies likely causes and gives you an evidence-based position if the matter escalates to a tribunal or insurer.
What records should I keep about cracking in my new build?
Photograph each crack with a scale reference (a ruler or coin) and a date. Mark the ends of the crack with a pencil so future photos can show whether it has lengthened. Note the date the crack was first observed, the room and element, and any related symptoms such as door binding. Keep all correspondence with the builder, any engineer reports and any rectification notices issued. A clear written record is essential evidence if the matter is disputed.