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Melbourne House Subsidence

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If the cracks in your walls are getting wider, your doors have started catching, or a floor has begun to slope, you may be looking at house subsidence: the ground beneath your Melbourne home sinking and taking the footings with it. It is not always as serious as it looks, and it is almost always fixable.

This page will help you work out what you are dealing with, how urgent it is, and what it is likely to cost before you call anyone. If you are also thinking about what this means for your property’s value, our guide on subsidence and property value covers that separately.

What is house subsidence?

House subsidence means the ground beneath part of your home is sinking, taking the footings with it and putting uneven stress on the structure above. Practically, this shows up as cracking, doors and windows that stick, or sloping floors. It does not automatically mean the house is unsafe, but it does mean the cause needs identifying before it gets worse.

Subsidence is the ground dropping away from a footing. Heave is the opposite: reactive clay swelling with moisture and pushing a footing upward. Both can crack a house, but the crack patterns tend to differ, which is one of the things a proper assessment establishes. Settlement, where a new building beds in evenly during its first year or two, and landslip, where a whole slope moves, are different again, and a professional assessment is what tells them apart.

In Melbourne the usual driver is reactive clay and the seasonal moisture cycle, which is why symptoms so often appear after an unusually dry summer or an unusually wet winter rather than gradually and evenly over time.

Signs of house subsidence

Several signs together point to subsidence. One sign on its own, especially a single small crack, usually does not.

Cracks that point to subsidence

Cracks that are wider at the top than the bottom. Cracks running diagonally, or stepping through brickwork. The same crack visible on both the inside and outside of a wall. New cracking that appears after a very dry or very wet spell.

Doors, windows and floors

Doors and windows that have started to bind or stick, floors that noticeably slope, and gaps opening up between walls and skirting boards. For homes where the floor itself is the main symptom, our sinking floors page covers it in more detail.

Signs that usually mean something else

Fine surface crazing in render or paint. Hairline shrinkage cracks in new plaster or a young concrete slab. Cracks that have not changed in years. Cracking confined to render, with no matching crack in the brickwork underneath.

The pencil and date test

This costs nothing and it is the single most useful thing you can do before calling anyone.

  1. Find the end of the crack, where it currently stops
  2. Draw a small pencil line across the crack at that point, and write today’s date next to it
  3. Do the same at the widest point of the crack
  4. Check back every few weeks
  5. If the crack extends past your pencil mark, or the width visibly changes, that is a sign of active movement worth getting assessed

Seasonal movement versus progressive movement

Reactive clay moves with the seasons, so some homes open and close small cracks slightly through the year without anything being structurally wrong. The concerning pattern is progressive movement: a crack that keeps growing over successive seasons rather than settling back down, or new cracks appearing in a pattern that spreads rather than staying put. A crack that has sat at the same width for years is a different situation to one that has visibly widened in the last month, even if the older crack looks bigger today.

When to call a structural engineer rather than a builder

A builder can tell you what a crack looks like. A structural engineer can tell you why it is happening and whether the structure itself is at risk, which is a different question. A repair contractor is naturally focused on the fix they can offer, which is a reasonable way to run a business but not always the most objective source of a diagnosis. An independent structural or geotechnical engineer has no stake in which repair method you eventually choose, which is exactly why their report carries weight with insurers, with buyers if you later sell, and with any repair contractor you engage afterwards.

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How serious is it?

Whether a crack is urgent depends far more on how it changes over time than on how wide it is on the day you first notice it. Movement over time is the signal, not a snapshot, which is why the pencil-and-date test above matters more than a single measurement.

What is urgent: cracks wide enough to fit a finger into; doors that will no longer close at all, not just stick; visible separation at the roofline; anything affecting a load-bearing wall.

What is usually not urgent: hairline cracks that have not changed in years; minor seasonal opening and closing of an existing fine crack; cosmetic cracking confined to render or cornices.

Crack width categories referenced by structural engineers are from AS 2870, and rather than publish approximate millimetre bands here, we recommend having a specific crack assessed directly against the standard. Whatever the pattern, the next step for anything beyond hairline, unchanging cracks is a proper assessment rather than a guess.

What causes subsidence in Australian homes

Subsidence in Australia is mostly driven by reactive clay and the seasonal moisture cycle, which behaves differently to the conditions covered in UK guides you may have come across, where clay content, rainfall patterns and drainage practices differ significantly.

Reactive clay and the seasonal moisture cycle

Reactive clay swells the ground in wet periods and shrinks it in dry ones. It is the dominant cause across most of the country. Melbourne sits on a mix of reactive clay through parts of the west and north and sandier profiles closer to the bay, so the same symptom can have a different underlying cause depending on where the property sits.

Drought, storms and flood water

Prolonged dry spells shrink clay away from footings and can leave voids beneath them. Storm and flood water does the opposite kind of damage, washing supporting material out from beneath footings.

Tree roots

Large trees draw moisture from the clay on one side of a house more than on the other, which is often why the worst cracking appears on the side nearest a mature tree.

Leaking stormwater or sewer lines

A cracked pipe, a blocked downpipe, or a disconnected gutter saturates one corner of a site over time, softening the ground only under that part of the house.

Poorly compacted fill and older footings

Fill that was never properly compacted, particularly on cut-and-fill blocks, settles under load. Older footings built before current standards accounted for reactive soil behaviour are more exposed to all of the above.

These causes rarely act alone. A property with moderately reactive clay might sit undisturbed for years until a nearby tree matures enough to draw significant moisture from one side of the yard, or until a gutter starts overflowing during heavier storms than the drainage was designed for. The underlying soil sets the risk, but it is often a specific, identifiable trigger that turns a stable site into one showing active movement. This is exactly why a site-specific assessment matters more than a general description like this one.

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What does it cost to fix subsidence?

Subsidence repair cost depends entirely on which fix your property actually needs, and the right answer ranges from nothing to tens of thousands of dollars.

Monitoring only: no direct cost beyond an assessment, for minor, non-progressive movement that does not yet need active repair. Drainage correction and root management vary by scope and are generally the least expensive active fix when water or tree roots are the identified cause. Resin injection: generally less than traditional underpinning, for void filling and lifting where the footing or slab is intact.

Minor underpinning: $5,000 to $10,000 for a single wall or small affected area. Moderate underpinning: $10,000 to $30,000 or more for a larger section of a house. Commercial or extensive underpinning: $30,000 to $100,000 or more for larger structures or extensive structural work. These bands reflect current pricing on our Melbourne underpinning page. They are indicative ranges, and a free on-site assessment turns a band into an exact, fixed price for your property.

What moves the figure

  • How much of the house is affected
  • Depth to stable ground
  • Site access for machinery or equipment
  • Which method is required
  • Whether cosmetic repair, such as re-rendering or crack filling, is included in the scope

An independent structural engineer’s report is worth budgeting for as a separate line item, distinct from the repair itself. It is often the most useful money spent in the whole process, since it establishes the actual cause before you commit to a fix. It is also worth comparing quotes on scope rather than headline price alone. A lower quote that covers only the underpinning work, with reinstatement, engineering, and cosmetic crack repair charged separately afterwards, can end up costing more overall than a higher quote that covers the full job upfront.

Is subsidence covered by insurance?

Most Australian home insurance policies exclude gradual earth movement and subsidence, though some cover sudden events, such as a burst water main causing rapid ground loss. It always depends on the specific policy wording, so this is a general position rather than an answer for your particular policy. Insurers typically assess whether the cause was sudden or gradual and whether a lack of maintenance, such as an unaddressed drainage problem, contributed to the damage.

Read your product disclosure statement, specifically the exclusions section. Photograph and date everything as early as possible. Get an independent engineer’s report before making a claim, as it objectively documents the cause. It is worth raising the issue with your insurer even if you suspect it will not be covered, since a documented claim history, even a declined one, can matter later if you sell the property or need to explain the repair history to a buyer’s engineer.

How Raise & Relevel can help

The right fix depends on the cause, not on a default method, and our free on-site assessment is where that gets established.

Monitoring: for minor, non-progressive movement, the correct next step is sometimes simply to track it over time rather than starting invasive work immediately. Drainage correction and root management: where water or tree roots are the identified cause, addressing that source can resolve the problem without any structural work at all. Resin injection: fills voids and can provide controlled lifting where the existing structure is basically sound; see our Melbourne resin injection page for how this works. Traditional underpinning: adds new structural support beneath a footing that can no longer carry its load; our Melbourne underpinning page covers the methods and costs in detail.

Where the issue is a sunken concrete slab rather than the building’s footings, Melbourne slab jacking is the more relevant fix, and where cracked concrete rather than settlement is the issue, our Melbourne crack injection page applies instead.

What to do next

  1. Photograph and date the cracks or symptoms you have noticed
  2. Check for obvious water causes, such as a blocked downpipe or a visible leak
  3. Monitor for a few weeks using the pencil and date test, unless anything looks urgent per the section above
  4. Get a professional assessment to establish the actual cause
  5. Talk to your insurer before committing to any repair work

A free on-site assessment is the practical next step once you have worked through the list above, not a sales pitch. The person who assesses your home is the person who would do the work. We have relevelled more than 7,000 homes, and every repair is backed by a 100-year product guarantee and a 50-year workmanship guarantee. Book a free on-site assessment, and we will confirm the cause and the right fix before any work begins, or call us on 1300 053 835 to talk to the team directly.

Why Raise + Relevel?

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Over 100 years of genuine experience in relevelling structures – we are ground surgeons.

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We stand behind the quality of our products and workmanship. Our warranty provides 100-year warranty on our resin products and 50-year warranty on our workmanship – If the problem returns, we return.

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FAQ

Your home is everything to you and your family, so before going ahead with any subsidence repairs, we’ve put together a list of questions our customers should ask:

It means the ground beneath part of your home is sinking, taking the footings with it and putting uneven stress on the structure above. Practically, this shows up as cracking, doors and windows that stick, or sloping floors. It does not automatically mean the house is unsafe, but it does mean the cause needs identifying before it gets worse.

Photograph and date what you are seeing, check for obvious water causes like a blocked downpipe, and monitor using the pencil and date test for a few weeks unless the signs already look urgent. From there, get a professional assessment to confirm the cause, and talk to your insurer before committing to any repair work. See What to Do Next above for the full sequence.

Minor underpinning, addressing a single wall or small area, generally runs from $5,000 to $10,000. Moderate underpinning across a larger section of a house generally runs from $10,000 to $30,000 or more, and commercial or extensive structural underpinning can run from $30,000 to $100,000 or more. A free on-site assessment turns these bands into a fixed price for your specific property.

It depends entirely on the cause and the fix required. Monitoring costs little beyond an assessment, drainage or root correction is generally the least expensive active fix, resin injection typically costs less than traditional underpinning; and underpinning itself ranges from around $5,000 for minor work to $100,000 or more for extensive projects. See What Does It Cost to Fix Subsidence above for the full breakdown.

Generally, no. Most Australian home policies exclude gradual earth movement and subsidence, though some do cover sudden events such as a burst water main. It always depends on your specific policy wording, so check your product disclosure statement directly rather than assuming either way, and get an independent engineer’s report to objectively document the cause.

A single small crack usually is not serious on its own. Watch for cracks that are wider at the top than the bottom, run diagonally, appear on both sides of the same wall, or keep growing over successive seasons rather than settling. The pencil-and-date test is the simplest way to track whether a crack is actively moving. See Is It Subsidence and How Serious Is It above for the full picture.

Yes, when the underlying cause is addressed alongside the visible symptom. If a repair only treats the crack or the sunken area without addressing the underlying cause, such as an unaddressed drainage problem or reactive soil movement, the same issue can return. A proper diagnosis before repair is what makes the fix durable rather than temporary.

It can, particularly if it is undisclosed or unresolved at the time of sale, since buyers and their engineers will often ask about any history of movement. A documented, properly repaired subsidence issue with an engineer’s report and a workmanship guarantee behind it is a very different position to an unexplained crack. Our blog post on subsidence and property value covers this in more detail.

Subsidence is the ground dropping away from a footing, while heave is the opposite: reactive clay swelling with moisture and pushing a footing upward. Both can crack a house, but the crack patterns typically differ, which is one of the things a structural assessment establishes when diagnosing the cause of movement.

We assess and repair subsidence across Melbourne, and more broadly across the states we operate in. Get in touch for a free on-site assessment to confirm coverage for your specific address.

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