What is subsidence? Subsidence is the sinking of the ground under a building, which leaves part of the house lower than the rest. It can happen slowly over years or suddenly after a leak or washout. Cracks, sticking doors and sloping floors are common signs. This guide explains the causes and the inspection, then covers what subsidence means for your home’s value and insurance.
What is subsidence?
Subsidence is the downward movement of the ground supporting a house, causing the footings to lose support and the building to move with it. In Australia, it’s often linked to clay soils drying out or getting wet, leaking pipes, tree roots, poorly compacted fill, and fill washing away. It is a ground problem first and a building problem second.
The words matter because engineers, insurers and buyers use them differently. A crack does not always mean subsidence, and subsidence does not always mean a house is unsafe.
Subsidence, settlement and heave: what is the difference?
Subsidence is the ground sinking under an existing building. Settlement is the normal compression of soil under new loads, usually in the first few years after construction. Heave is the opposite of subsidence: the ground swells, pushing the house up. All three can crack walls, so a report should say which one is happening.
| Term | What it means | What it usually points to |
| Subsidence | The ground under the house sinks | Drying clay, leaks, erosion or poor fill |
| Settlement | Soil compresses under the building’s weight | Normal in the early years; a concern only if it continues |
| Differential settlement | One part of the house moves more than another | The type of movement that causes most cracking |
| Heave | Ground swells and lifts part of the house | Clay is getting wetter, often from leaks or poor drainage |
| Erosion | Soil washes away from underfootings | Burst pipes, stormwater or broken drains |
| Landslip | Soil moves downhill on a slope | Sloping sites, saturated ground or cut and fill |
What causes subsidence?
Most subsidence in Australian homes comes from changes in soil moisture. Reactive clay shrinks as it dries and swells as it gets wet. When one side of a house gets wetter or drier than the other, the footings move unevenly. Leaks, trees, poor drainage, weak fill and erosion are the usual triggers.
CSIRO’s homeowner guide to foundation maintenance and footing performance explains how moisture changes in clay can move footings and why even a small leak can saturate the clay beneath a house. The common causes are:
- Reactive clay drying and wetting. Long dry spells shrink clay, then heavy rain swells it again. Our guide to reactive clay and moisture explains why this is so common.
- Water leaks. A leaking water pipe, sewer line, or stormwater drain can soften or wash away soil. Read how water leaks cause subsidence and foundation movement.
- Trees. Large trees near the house draw moisture from the clay, especially inespecially in dry months.
- Poor fill. Soil that was not properly compacted during site preparation can compress beneath the house.
- Poor drainage. Water is pooling against the footings, or gutters and downpipes are discharging next to the walls.
- Slopes and erosion. Soil movement on a slope, or ground washing away after storms.
Finding the cause matters as much as fixing the damage. A repair that leaves a leak running can fail.
What are the signs of subsidence?
Common signs of subsidence include diagonal cracks near doors and windows, cracks that are wider at one end, doors and windows that stick, gaps under skirting boards, sloping floors and cracks in paths near the house. One sign alone rarely proves subsidence. A pattern of signs on one side of the house is more telling.
| What you notice | What it might mean |
| Diagonal cracks from the corners of doors or windows | Differential movement in the walls |
| Cracks widen at the top or bottom | One part of the house is moving more than another |
| Doors or windows that stick or will not latch | Frames pulled out of square |
| Gaps between skirting boards and the floor | Floor dropping or lifting |
| Sloping or uneven floors | Movement under a slab or footing |
| Cracks that open and close with the seasons | Seasonal clay movement |
Our guide to the most common signs of subsidence in homes covers each sign in more detail. If you are unsure whether a crack matters, read “Is it just a crack or a structural issue? and see our cracked walls, sinking floors and jammed doors and windows pages.
How is subsidence inspected?
A subsidence inspection determines whether the house is moving, how much, why, and whether the movement has stopped. A structural engineer usually measures floor levels, records crack widths and patterns, and assesses drainage, plumbing, trees,s and soil. A geotechnical investigation or plumbing leak test may follow when the cause is unclear.
The answer to one question shapes everything after it: Is the movement still happening?
| Movement status | What it means | What usually happens next |
| Active | The house is still moving | Find and fix the cause; monitor; plan repairs |
| Seasonal | Cracks open and close with wet and dry periods | Moisture control first; repair once stable |
| Historical | Movement happened in the past and has stopped | Cosmetic repair may be enough, with records kept |
| Uncertain | Not enough information yet | Monitor crack widths and floor levels over time |
Engineers often grade wall cracking using the damage categories outlined in AS 2870, as set out in CSIRO’s guide for homeowners. The categories run from hairline cracks under 0.1 mm to very severe damage with cracks wider than 25 mm.
| Category | Description | Approximate crack width |
| 0 | Negligible | Under 0.1 mm |
| 1 | Very slight | Under 1 mm |
| 2 | Slight | Under 5 mm |
| 3 | Moderate | 5 to 15 mm |
| 4 | Severe | 15 to 25 mm |
| 5 | Very severe | Over 25 mm |
Check that your engineer is qualified. You can search the National Engineering Register run by Engineers Australia. Our guide to diagnosing an unlevel building explains the tests involved.
How does subsidence affect your home’s value?
Subsidence can lower a home’s value, but no single reliable percentage applies to every house. The effect depends on how severe the movement is, whether it is still active, whether the cause has been fixed and how well the repairs are documented. A house with repaired, engineer-certified subsidence usually worries buyers far less than one with active, unexplained movement.
Buyers react to the evidence in front of them:
| What the buyer sees | Likely reaction |
| Fresh cracks with no report | Walks away, or offers well below asking to cover unknown costs |
| An engineer’s report confirming active movement | Negotiates on price or asks for repairs before settlement |
| Repairs completed with an engineer’s sign-off and warranty | Treats it as a known, resolved issue |
| Old, stable cracks with monitoring records | Lower concern, especially if the cause was fixed |
Valuers and lenders look at the same evidence. A valuer may note structural movement in a report, and a lender may ask for an engineer’s report before approving a loan. You can find a certified valuer through the Australian Property Institute.
If you are selling, disclosure rules vary by state, so get legal advice early. If you are buying, our guide to buying or selling a house with subsidence lists the documents to ask for.
Keep these records to protect your home’s value:
- Engineer’s reports, before and after repair.
- Plumbing or leak test results and repair invoices.
- Repair scope, drawings and completion certificate.
- Warranty documents for the work.
- Dated photos and crack or floor-level monitoring records.
Does home insurance cover subsidence?
Sometimes. Many home insurance policies exclude damage from gradual ground movement, but they may cover damage caused by a sudden insured event, such as a burst pipe that washes soil away. The product disclosure statement (PDS) for your policy decides it. Read the definitions and exclusions before you make a claim or start repairs.
Clauses to look for in your PDS include:
- Exclusions for gradual movement, settlement, shrinkage or expansion of soil.
- Exclusions for damage that existed before the policy started.
- Exclusions linked to poor maintenance, such as long-running leaks.
- Exclusions for faulty design or artistry.
If you claim, keep photos, reports and repair quotes. Insurers that subscribe to the General Insurance Code of Practice must follow set timeframes, including keeping you updated at least every 20 business days and deciding most claims within four months [verify against the current Code before publishing]. ASIC’s Moneysmart explains how to choose home insurance and make a home insurance claim.
How is subsidence repaired?
Subsidence is repaired by fixing the cause, then restoring support under the house, and then repairing the visible damage. The method depends on the soil, the depth to firm ground and how far the house has moved. Common options include resin injection, underpinning, slab jacking and void filling, often combined with drainage or plumbing repairs.
- Resin injection fills voids and compacts weak soil under footings and slabs, and can lift the house in controlled steps.
- Underpinning extends or deepens footings so they rest on firmer ground.
- Slab jacking lifts a sunken concrete slab back towards level.
- Void filling fills gaps under slabs where soil has washed away.
- Water leak management finds and fixes the leaks behind the movement.
Our comparison of underpinning, re-levelling, and slab lifting explains when each is appropriate. For a real example, see our home stabilisation and subsidence correction project. Our subsidence repair service covers the full process.
Can you prevent subsidence?
You cannot control the soil, but you can control most of the triggers. Keeping moisture around the house is the most useful step. That means fixing leaks quickly, keeping drains clear and managing trees and garden watering near the footings.
- Fix leaking taps, pipes and drains as soon as you notice them.
- Make sure downpipes discharge away from the house.
- Grade the soil and paving so water runs away from the walls.
- Keep large trees a sensible distance from the house, and get advice before removing an established one.
- Avoid heavy watering of garden beds right against the footings.
- Watch existing cracks and note any change.
Our guide on protecting your house from ground subsidence includes more steps.
Frequently asked questions
Is subsidence the same as settlement?
No. Settlement is the normal compression of soil under the weight of a building, mostly in the first few years after construction. Subsidence is the ground beneath an existing house sinking, often due to drying clay, leaks, or erosion. Settlement usually slows and stops. Subsidence can continue until the cause is found and fixed.
Can subsidence be fixed permanently?
Subsidence can usually be repaired in the long term when the cause is fixed and the footings are properly supported. A repair that ignores the cause, such as a leaking pipe or poor drainage, may not last. Ongoing moisture control around the house is part of a lasting fix.
Can you sell a house with subsidence?
Yes. Houses with subsidence are bought and sold, but the price and the number of interested buyers depend on the evidence. An engineer’s report, completed repairs and warranty documents help buyers judge the risk. Disclosure rules vary by state, so get legal advice before you list.
How much does subsidence repair cost?
Subsidence repair costs vary widely. The price depends on the cause, the repair method, the depth to firm ground, site access and the amount of lift needed. Minor crack repairs cost far less than structural work. A site inspection and an engineer’s assessment are needed before a reliable quote can be given.
When should you get a subsidence inspection?
Get a subsidence inspection when cracks are growing, new cracks appear, doors or windows start sticking, floors begin to slope, or you are buying a house with visible cracking. Earlier inspection usually means a simpler repair because the cause can be addressed before further movement occurs.
Protect your home and its value.
So, what is subsidence? It is the ground beneath your home sinking, usually due to changes in soil moisture, leaks, trees, or poor fill. Left alone, it can damage the building and worry buyers and lenders. When caught early, properly diagnosed, and repaired with good records, it can usually be fixed, and its effect on value reduced.
If you have noticed cracks, sticking doors, or sloping floors, our team can inspect your home, identify the cause, and explain your repair options. We have re-levelled more than 7,000 homes across New South Wales, Victoria, Queensland and the ACT.
Book a subsidence inspection or call 1300 053 835.
