CSIRO’s homeowner guide Foundation Maintenance and Footing Performance states that “Buildings can and often do move”, and relates it usually to problems in the foundation soil. Its damage table, from AS 2870-2011, grades wall cracks from category 0, hairline cracks under 0.1 mm, to category 4, severe, at 15–25 mm but also depending on the number of cracks. It states: “In general, most cracking found in masonry walls is a cosmetic nuisance only”, and also that “monitoring of cracks in walls and floors should always be treated seriously.” This note quotes the guide and NCC 2022; it does not say whether a particular crack is a defect.
Is it normal for a new house to have cracks?
The CSIRO guide, published in 2024 as a Building Technology Resource that replaces Building Technology File 18, opens: “Buildings can and often do move. This movement can be up, down, lateral or rotational.” It continues: “The fundamental cause of movement in buildings can usually be related to one or more problems in the foundation soil.”
For a newly built house, the guide describes two kinds of settlement caused by construction. Immediate settlement “occurs when a building is first placed on its foundation soil”, and granular, particularly sandy, soil is susceptible to it. Consolidation settlement “is a feature of clay soil” and “will usually take place during the first few months after construction but has been known to take many years in exceptional cases.” The guide says these problems “may be the province of the builder and should be taken into consideration as part of the preparation of the site for construction.” It says this in the context of site preparation; it does not say who is liable for, or must repair, cracking in a finished house.
On how cracks behave afterwards, it states: “In the event of construction settlement, cracking will usually remain unchanged after the process of settlement has ceased.” The guide does not say whether a given crack in a given house comes from settlement; that needs an inspection of the building.
How wide is a hairline crack, and how are cracks graded?
Under the heading Seriousness of cracking, the guide states: “In general, most cracking found in masonry walls is a cosmetic nuisance only and can be kept in repair or even ignored.” CSIRO’s Table 2, which it reproduces with permission from Table C1 of AS 2870-2011, grades damage to walls by approximate crack width: category 0, Negligible (hairline cracks, under 0.1 mm); 1, Very Slight (under 1 mm); 2, Slight (under 5 mm); 3, Moderate (5–15 mm, or a number of cracks 3 mm or more in one group); and 4, Severe (15–25 mm, but also depending on the number of cracks). The table also describes typical damage and repair for each category; the full table is in the CSIRO guide linked in the sources.
The guide adds that AS 2870-2011 also publishes figures for cracking in concrete floors, which it does not reproduce “because wall cracking will usually reach the critical point significantly earlier than cracking in slabs”. The guide does not connect the categories to a builder’s obligations or to warranties. It reproduces the 2011 edition of AS 2870, and this note does not describe the current edition.
What causes settlement and movement cracks in houses?
The guide splits foundation soils into two approximate groups, granular and clay, and notes that soil is often a mixture. Problems with granular soils “are usually caused by erosion”, while “Clay soils are subject to saturation and swell/shrink problems.” It states: “As most buildings suffering movement problems are founded on clay soils, there is an emphasis on classification of soils according to the amount of swell and shrinkage they experience with variations of water content.”
The causes it lists include settlement due to construction, erosion, saturation, seasonal swelling and shrinkage of clay, shear failure and tree root growth. On water it says: “Even a minuscule leak can be enough to saturate a clay foundation.” It names leaking water service, sewer and stormwater pipes, leaking taps, trenches that carry water, and roof plumbing problems such as overflowing gutters and downpipes not connected to a stormwater system.
The guide does not discuss any city or suburb. It states that “Generally soil classification is provided by a geotechnical report.” Under the NCC Housing Provisions the class is given to the site under AS 2870, as the site classification note explains.
What do movement cracks look like in brick, framed and brick veneer houses?
For brickwork that loses support, the guide lists symptoms including “Step cracking in the mortar beds in the body of the wall or above/below openings such as doors or windows” and “Vertical cracking in the bricks”. It says brickwork “will attempt to span areas that lose support”, so “It is therefore usual to see cracking at weak points, such as openings for windows or doors.” Swelling clay can first show as a slightly dished floor, “often accompanied by some doors binding on the floor or the door head, together with some cracking of cornice mitres.”
Timber or steel framed buildings, the guide says, “are less likely to exhibit cracking due to swell/shrink than masonry buildings because of their flexibility”, though added stress “can create cracking in wall linings, particularly where there is a weak point in the structure caused by a door or window opening.” A brick veneer building “can be expected to behave as a framed structure, except that the external masonry will behave in a similar way to the external leaf of a full masonry structure.”
For full masonry structures, where swelling after construction causes cracking, the guide says that each time the swell/shrink cycle repeats, the cracking is likely to become wider “until the sections of brickwork become virtually independent”. It says that once cracking is established, if there is no other complication, “it is normal for the incidence of cracking to stabilise”. It adds: “This is by no means always the case, however, and monitoring of cracks in walls and floors should always be treated seriously.”
What about plaster cracking and hairline cracks in render?
The CSIRO guide is about soil-related building movement. It describes cracking in wall linings of framed buildings and in masonry, but it does not discuss shrinkage of plaster or render as materials, and it gives no cause for a particular hairline crack. Its table places hairline cracks under 0.1 mm in category 0, Negligible, in a classification of damage “with reference to walls”.
Articulation joints in masonry walls, as clause 5.6.8 of the NCC Housing Provisions describes them, are covered in a separate note. Whether a crack in a lining or render is cosmetic, or a sign of movement in the footings, is a question for someone who has inspected that house.
What does the guide suggest to limit soil movement around a house?
Under Prevention and cure, the guide says that where movement is caused by water service, roof plumbing, sewer or stormwater failure, “the remedy is to repair the problem.” It recommends that, “particularly where problems exist or are likely to occur”, an apron of paving be installed around as much of the building perimeter as necessary, extending outwards “a minimum of 900 mm (more in highly reactive soil)” with “a minimum fall away from the building of 1:60”, and finished “no less than 100 mm below brick vent bases.” These are the guide’s maintenance recommendations, not NCC provisions.
It also covers garden layout, stating that “Overwatering due to misuse of automatic watering systems is a common cause of saturation and water migration under footings”, and subfloor condensation, where it calls an adequate subfloor ventilation system “desirable”. On repairs it states: “Remediation of footings and foundations is generally the realm of a specialist consultant.”
Where do the NCC and AS 2870 come in?
Performance Requirement H1P1 in NCC 2022 Volume Two requires a building or structure, during construction and use, with appropriate degrees of reliability, to “perform adequately under all reasonably expected design actions”, among other things. H1D4(1) states that H1P1 “is satisfied for the design and construction of footings and slabs” if they comply with AS 2870 or AS 3600, or, subject to H1D4(2), Section 4 of the ABCB Housing Provisions. Those are Deemed-to-Satisfy routes; a Performance Solution is the other route. The South Australian schedule to Volume Two does not vary H1D4.
Within the Section 4 Deemed-to-Satisfy route, which H1D4(1)(b) makes subject to H1D4(2), clause 4.2.2 of the Housing Provisions requires the foundations where footings and slabs are to be located to be “classified in accordance with AS 2870”. The NCC calls up AS 2870; this note does not describe that Standard beyond what CSIRO reproduces from its 2011 edition.
This note quotes NCC 2022. The ABCB records that NCC 2025 was published on 1 May 2026 and lists South Australia’s NCC 2025 adoption dates as 1 May 2027 for the BCA and 1 May 2026 for the PCA. The relevant authority assessing the building work confirms which edition applies to a particular application.
Is a crack in a new house a defect the builder must fix?
This note does not answer that, and the CSIRO guide does not either. Whether a crack is a defect, and who is responsible for it, depends on the contract, the statutory warranties and the facts of the building. The statutory warranties note sets out what the Law Handbook records about them.
The guide’s own disclaimer reads: “Seek specialist advice for your particular circumstances.” On footings, it says remediation is “generally the realm of a specialist consultant.” Questions about rights and disputes are covered, with their sources, in the warranties note.
Common Questions
Is it normal for a new house to have cracks?
CSIRO’s homeowner guide Foundation Maintenance and Footing Performance (2024) states that “Buildings can and often do move”. Of consolidation settlement, which it calls “a feature of clay soil”, it says it “will usually take place during the first few months after construction but has been known to take many years in exceptional cases.” It states: “In general, most cracking found in masonry walls is a cosmetic nuisance only”, and also that “monitoring of cracks in walls and floors should always be treated seriously.” Whether a particular crack is expected movement or a defect needs an inspection of that house; the guide does not decide it.
How are wall cracks graded by width?
The CSIRO guide Foundation Maintenance and Footing Performance reproduces, with permission, Table C1 of AS 2870-2011, which grades wall damage by approximate crack width: hairline cracks under 0.1 mm are category 0, Negligible; under 1 mm, category 1, Very Slight; under 5 mm, category 2, Slight; 5–15 mm, or a number of cracks 3 mm or more in one group, category 3, Moderate; and 15–25 mm, but also depending on the number of cracks, category 4, Severe. The table classifies damage; it does not say who repairs it or whether it is a defect in a new house.
What causes settlement cracks in a new house?
The CSIRO guide Foundation Maintenance and Footing Performance describes immediate settlement, when soil compacts under the new building, and consolidation settlement in clay soil, which it says usually happens during the first few months after construction and, in exceptional cases, over many years. It lists other causes of movement including erosion, saturation from leaks, seasonal swelling and shrinkage of clay, and tree roots. The cause of a specific crack needs an inspection.
Are hairline cracks in plaster or render a problem?
The CSIRO guide Foundation Maintenance and Footing Performance covers soil-related building movement; it does not discuss shrinkage of plaster or render as materials, so it does not explain the cause of a given hairline crack. In its damage table, reproduced from AS 2870-2011 and graded with reference to walls, hairline cracks under 0.1 mm are category 0, Negligible. Someone who inspects the house can say whether it is cosmetic or a sign of movement.
Does the NCC set a crack width limit for a new house?
NCC 2022 Volume Two H1D4(1) is a Deemed-to-Satisfy Provision that treats footings and slabs as meeting Performance Requirement H1P1 if they comply with AS 2870 or AS 3600, or Section 4 of the Housing Provisions within the limits of H1D4(2). The NCC text read for this note does not itself state a crack width limit; the crack-width grading described here is from AS 2870-2011, as reproduced by CSIRO. The relevant authority confirms which edition of the NCC applies.
Sources
- CSIRO, Foundation Maintenance and Footing Performance: Preventing soil-related building movement (Building Technology Resource, 2024; replaces Building Technology File 18)Accessed 2026-11-10
- NCC 2022 Volume Two — Part H1 Structure (H1P1, H1D4)Accessed 2026-11-10
- NCC 2022 Volume Two — Schedule 8 South Australia, Part H1 StructureAccessed 2026-11-10
- NCC 2022 ABCB Housing Provisions — Part 4.2 Footings, slabs and associated elements (clause 4.2.2)Accessed 2026-11-10
- ABCB — NCC 2025 state and territory adoption informationAccessed 2026-11-10
This page describes these sources as they stood on the access dates above. It is not legal advice about any particular property.
Planning a rebuild or new build in Adelaide? Start with a free initial consultation.