Understanding cracking in Wollert homes on reactive clay
How to read cracks in a Wollert house, what the Guide to Standards and Tolerances allows, and when cracking points to footing movement.
In short: Not every crack is a structural problem, and not every hairline is harmless. What the width, the pattern and the season tell you about what is happening underneath.
Why cracking is common on the basalt plains
The reactive clay above the Newer Volcanics basalt swells with winter rain and shrinks through summer. A house sitting on that clay moves with it. Some movement is expected and is what the footing system is designed to accommodate. Cracking becomes a defect when the width, the pattern or the rate of change goes beyond what the design and the tolerances allow.
Width categories and what they mean
The Guide to Standards and Tolerances 2015 sets out crack width categories for masonry and internal linings in Victoria, and AS 2870 describes damage classifications for houses on reactive sites. Cracks that are wide enough to admit a fingernail, that step through brickwork or that are still opening are a different conversation.
Pattern tells you more than width alone
Diagonal cracks running from window and door corners suggest differential movement in the footing system. Vertical cracks at articulation joints are usually doing their job. Stepped cracking through brick perpends that widens toward the top of a wall points to one corner lifting or dropping.
The other symptoms that go with movement
Cracking rarely travels alone. Doors that bind in winter and swing freely in summer, gaps opening between cornice and ceiling, skirting lifting off the floor, tiles drumming or cracking in a line, and windows that no longer latch are all worth recording. A pattern of symptoms across one part of the plan is more telling than any single crack.
Monitoring before you demolish anything
Where movement may still be active, the sensible first step is monitoring rather than rectification. Marking, measuring and photographing the same cracks across a wet and a dry season shows whether they are seasonal and stable or progressive. Repairing a crack that is still moving simply buys a repeat performance the following year at your own cost.
What causes it, and what fixes it
Common causes here are moisture variation around the footings, poor site drainage, plumbing leaks, trees close to the slab, and inadequate footing design for the site classification. The fix follows the cause. Patching without addressing drainage or a leak is cosmetic. That is why a defect investigation looks at the whole site, not only the wall that cracked.
Where it sits under Victorian warranties
Structural building work in Victoria is subject to a ten year limitation under s 134 of the Building Act 1993, running from the occupancy permit. If cracking appears within that window and stems from footing design or construction, it is worth getting it assessed properly rather than waiting to see whether it gets worse.
Written by the Owner Inspections team from inspections carried out in Wollert. Licensed building practitioners, Building & Plumbing Commission registration CDB-U 53425.
