Foundation Repair Adelaide: Cracked Walls, Sinking Floors, Subsidence and Levelling Explained

• What it is: work that stops a house foundation moving and, where needed, brings it back to level. It ranges from fixing a leaking drain to underpinning with concrete or piles, filling voids, and lifting a dropped floor or slab.
• Start with the cause: CSIRO's Building Technology File 18 says that where movement comes from plumbing or stormwater failure, the remedy is to repair the problem. A repair that ignores the cause tends to be a repeat job.
• Cracks: CSIRO sorts wall cracks by width, from hairline under 0.1 mm, which is negligible, to 5 to 15 mm, which it calls moderate. Width, pattern and whether the crack keeps growing all matter.
• Adelaide ground: state mines department Information Sheet 16 names three problem soils here: expansive clay, collapsing soils and soft compressible soils. Each moves differently.
• Levelling and underpinning: underpinning stops movement and levelling reverses a drop. Some homes need both, some need one, and some need neither once a leak is fixed.
• Slabs and driveways: sunken concrete can often be lifted by injection, though one platform guide warns that clay which shrinks and swells with the seasons can make lifting less certain than it looks.
• Cracks after repair: the walls are repaired once the foundation has stopped moving, not before.
• Cost: this page quotes no price. The ranges that have been published are lined up, with sources, under underpinning cost.
• Next step: send photos of the cracks, floors and doors, with a short note, and a site visit can lead to a written quote.

Foundation repair Adelaide owners ask about usually begins with a handful of signs. Cracks in brick walls come first for most people, often running diagonally from the corners of doors and windows. Sticking doors, windows that no longer close, gaps opening between walls and ceilings, floors that slope or bounce, uneven floors and floor coverings that split along a line are the others. CSIRO's Building Technology File 18 lists step cracking in the mortar beds and vertical cracking in the bricks as typical evidence of footing failure, and notes that cracking tends to appear at weak points such as openings for windows and doors.

The signs overlap, so no single one gives the answer. A door that sticks can mean a footing has dropped, a floor has domed after a wet winter, or the timber has swollen in humid weather. A sloping floor can come from a sunken slab, a settled stump or a dished foundation. What helps is the combination, the history and the timing: whether a sign appeared after a burst pipe, after a very dry summer, after a tree was planted or removed, or after building work next door.

Look at how the signs are spread across the home. Movement at one corner points toward a local cause such as a leaking pipe, a downpipe emptying beside the footing or a large tree, while settlement across the whole house points toward seasonal swelling of clay or weak ground. CSIRO notes that building movement is usually rotational, so the visible symptoms, such as a door binding on its frame, do not simply reflect the original cause. That is why a repair quote written from a photograph is a guess: a structural engineer reads the whole home, and the foundation repair that follows depends on what they find. To follow the same signs on a house over several seasons, see house underpinning.

CSIRO notes that most cracking in masonry and brick walls is cosmetic, and may be patched as needed or left alone, but that applies only to cracks that stop growing. Mainmark takes a similar line, saying hairline cracks under 1 to 2 mm are often cosmetic and cracks wider than 5 mm, or ones that spread quickly or form a stepped pattern, deserve professional help.

What the crack does over time matters as much as its width. Pencil a dated tick at each end of the crack and photograph it beside a ruler. Measure again after a wet spell and again after a dry one. In CSIRO's explanation, cracking from a footing that failed through erosion keeps developing until the cause is dealt with, while cracking from settlement during construction tends to stay as it is once the settling ends. Seasonal swelling and shrinking is different again: each wet and dry cycle can widen cracks that formed earlier, and the same source expects the cracking to partly remain once the shrinking part of the cycle is over.

Stair step cracks follow the mortar joints in the brickwork, diagonal cracks radiate from the top and bottom corners of openings, and gaps form where walls meet ceilings or floors. Brickwork around windows and doors is the usual weak point, windows can stick before any crack shows, and gaps open above lintels and at the corners of windows. Cracks that pass through the bricks rather than around them are the vertical cracking CSIRO lists as a sign of footing failure, and a structural crack of this kind deserves attention sooner than a hairline crack in plaster. Cracks that open and close with the seasons point to clay and moisture. Cracks that keep opening in the same direction point to a footing that has moved and not recovered. A crack that showed up straight after a burst pipe or a big storm is worth a phone call that week. Cracks beside a large tree, over a drain run or under a downpipe point to water. Photograph every window and door that sticks, because windows and doors often show foundation movement first, and stiff windows may be the earliest sign.

Cracked wall repair, meaning filling, repointing and repainting, is a separate job from foundation repair. A cracked wall that has stopped moving can be repaired and a cracked wall that is still moving cannot, so wall crack repair belongs at the end of the job. Wall cracks in brickwork are repaired differently from wall cracks in plaster or render, and the trade that repairs brickwork may not be the one that repairs plaster. The usual order is cause first, foundation second and wall repair last, so the repair is not undone by further movement. Mainmark and OB Engineering both say cracks that have formed usually need their own repair once stability is achieved.

The ground under Adelaide homes varies more than most owners expect. A state mines department publication for home builders, Information Sheet 16, identifies three main problem soils in the Adelaide region. Expansive soils are clays that expand with moisture and contract as they dry, and the sheet blames that change in volume for much of the wall cracking seen across Adelaide. Collapsing soils are fine limy silts or loose wind-blown sand that lose strength when wetted beyond a certain limit and can settle suddenly even under their own weight. Soft or compressible soils, made of silt, fine sand and mud, cannot carry building loads without long-term settlement, and the sheet says they occur chiefly on coastal river estuaries with high water tables, including large reclaimed tracts used for housing.

Each type produces a different kind of foundation problem. Expansive clay produces cycles of lifting and dropping with the weather. Collapsing soil produces sudden settlement after a leak or heavy wetting. Soft ground produces slow settlement that can continue for a long time. The sheet adds that its soil maps are approximations that should not replace a soil investigation.

Water changes all of them, and on reactive clay a wet winter and a dry summer can each move the foundation, so reactive clay beside a leaking drain moves more than most soil. CSIRO warns that a very small leak can saturate clay beneath a footing, that pipe trenches can act as watercourses even after backfilling, and that downpipes not connected to a stormwater system direct water to the soil beside the footings, sometimes causing erosion, saturation and migration of water under the building. Leaks, poor drainage, roof run-off and garden watering are therefore the first suspects whenever a foundation moves, and the simplest to rule out.

Trees are the other usual suspect. CSIRO explains that growing roots can push up on footings, while soil dried by tree or shrub roots tends to shrink and remove support. A large tree close to the house, or one removed or planted near the foundation, changes the moisture in the clay, and the effect can take a season or more to show. Read the underpinning Adelaide overview for how this fits with the main repair methods.

Fixing the cause is the first step in foundation repair, and CSIRO treats it as the first remedy. Where movement traces back to a leaking water service, a roof plumbing fault, or a sewer or stormwater line, CSIRO's remedy is simply to repair that fault. It also suggests thinking about rerouting pipes away from the building and moving taps so leakage cannot run toward the footings. A plumber's camera inspection and a pressure test of water services can rule leaks in or out before any foundation work is priced. Drainage faults that wet the soil beside brickwork and windows show up as cracks and gaps there first, so drainage is checked and drainage repairs are made before any wall is touched. If the roof or its plumbing proves to be the source, Adelaide Roof Repairs is a separate site that covers roof repairs.

Surface water deserves its own check. CSIRO suggests inspecting during and after heavy or prolonged rain to see where water flows, and says a grated drain connected to the stormwater system is usually an easy solution. It points out that the soil affecting footings extends well beyond the building line, and that watering garden plants, shrubs and trees causes some of the most serious water problems.

For problem sites CSIRO recommends an apron of paving around as much of the perimeter as necessary. The apron should extend outward at least 900 mm, more in highly reactive soil, with a fall away from the building of at least 1:60, and the finished paving should sit no less than 100 mm below brick vent bases. These are general guidance figures from a technical note, not a specification for your home.

Subfloor ventilation completes the list for homes with a floor void. CSIRO warns that poor ventilation causes condensation and slows the drying of soil beneath the house. Trees should be assessed with the engineer, because removing a large tree beside a footing can itself cause the clay to swell. Plumbing, drainage and tree work may be enough on its own, or may be needed before any underpinning is worth doing, which is why a good foundation repair quote starts with a list of what was checked.

Moisture is the thread running through every one of these checks. A damp patch beside a wall, water pooling after rain, soil that cracks open in summer and tree roots reaching under a footing are all signs that the moisture around the foundation is changing. Reactive clay is the reason this matters in Adelaide: the soil swells as water arrives and shrinks as it leaves, and drainage that sends water to the same spot for months can make the soil movement worse. Tree roots take water from the clay, and a void can form where soil has shrunk away or washed out, so checking for voids belongs in the same inspection, along with the drainage, the soil moisture and the tree roots.

A sinking house is rarely sinking evenly. What owners call a sinking foundation is usually one part of the foundation settling more than the rest, which tilts floors, opens cracks and twists door frames. This kind of foundation settlement has a handful of mechanisms, and each leaves different clues. Water washing soil from under a footing, a clay foundation drying out beside a tree, loose fill compacting under a slab and soft ground consolidating slowly can each produce a sinking house, and each needs a different foundation repair.

Erosion is the clearest case. CSIRO explains that erosion removes support from under footings, tending to create subsidence of the part of the structure under which it occurs. A broken drain, a leaking tap or a downpipe emptying at the corner of the house can carry fine soil away and leave a void, and house subsidence of that kind tends to be local, so one corner or one wall drops while the rest stays put. The movement continues until the cause is fixed. Void filling beneath the footing is one published repair for it, as is underpinning to firm ground, but neither lasts if the leak continues.

Shrinking clay is the slower case. Where a tree or a dry summer draws moisture out of expansive clay, the foundation can drop where the drying is strongest and the movement is seasonal. Foundation movement of this kind opens cracks in summer and may close them in winter, and sinking floors and uneven floors can come and go with the weather. A repair that treats it as permanent settlement may be solving the wrong foundation problem.

Collapsing and soft soils are different again. The Department of Mines and Energy says collapsing soils can settle suddenly when wetted, and that soft compressible soils settle slowly over the long term. In both cases the sinking foundations reflect weak ground, and the ground, not the walls, is what a foundation repair has to deal with. That is why engineers ask for soil information before recommending underpinning, piles or injection.

Whatever the mechanism, the first diagnosis is simple to describe. Is the house still sinking? Is the movement local, with one corner of the house dropping, or across the whole house? Is there a water, tree or soil cause that can be found and stopped? Answering those questions turns a vague sinking house into a defined foundation problem, and a defined problem is one a business can quote on in writing. Movement that is slow, local and tied to a leak is a very different home problem from movement that is fast, wide and tied to weak ground, and the soil moisture and any void under the foundation help tell the two apart.

House levelling, also written house re-levelling, corrects a home that has already dropped or tilted. Underpinning aims to stop movement and levelling aims to reverse its effect, which is why the two are so often discussed together. JR Southern Underpinning puts it plainly: if a home has dropped on one corner it typically needs both, underpinning to secure the footing on stable ground and levelling to lift the structure back to level. It adds that levelling without underpinning means the home can simply drop again, while underpinning without levelling leaves the slope.

Not every home fits that pattern. A home that has cracked and moved but has not dropped much out of level may need stabilising only. A home whose floors slope because a leak washed out the soil under one footing may need the leak repaired, voids filled and a controlled lift. Resin businesses such as Mainmark describe injection as stabilising the ground, re-levelling and re-supporting in one process, so on their account a separate lift is not needed. The honest summary is that the sources differ on how often both are needed, and an inspection decides it for your house.

Levelling is the last stage of a lift, not the first. Levelling a home that is still settling wastes the lift, while levelling done after the foundation is stable is more likely to hold. Levelling targets are set by the engineer, and levelling by injection or by jacks is checked at every stage. Two questions help. First, has the home moved down, or is it still moving? Underpinning answers a continuing movement, and levelling answers a completed drop. Second, how much lift is wanted? CSIRO's damage classes put slightly sticking doors at the slight end, and lifting a home all the way back to level is not always wanted or possible. Many owners ask only that the home stop moving and that the worst slopes be eased, and an engineer can set a realistic target.

House re-levelling in practice is a controlled lift. Mainmark and other resin businesses describe re-levelling a home by injecting material under the foundation until the floors rise, while house levelling by traditional methods uses jacks to lift the structure onto new support. Either way, the lift is made in small stages with levels checked, because re-levelling a house too fast can crack walls that have settled into their new position. Re-levelling does not repair the cause of a sinking foundation, so house levelling is done after the leak, drain or tree problem has been dealt with, and the engineer sets the target for the re-levelling. Some owners ask for re-levelling to ease the worst floor slopes and accept small differences, because a perfectly level result may cost more cracking than it cures. Staged levelling is easier to stop if a wall starts to crack, and a house that is re-levelled and then monitored for a season gives clear evidence that the foundation repair worked.

Ask what the lift will do to the walls. Raising one part of a house changes the stresses in the rest, and cracks that closed during settlement can reopen. A proposal should say how levels will be monitored during the lift, how the lift will be stopped if walls start to crack, and how the cracks will be repaired afterward. Lifting by injection is explained under resin injection underpinning, and lifting with concrete or piles under house underpinning.

Subsidence repair is an everyday phrase for a specific problem: the ground under part of a building has dropped or lost support, and the building above has followed. CSIRO says erosion is one cause, and that older masonry has little resistance to the loss of support, so brickwork cracks as it tries to bridge the gap.

Subsidence repair follows the same logic as every other foundation repair. Settlement of the foundation, whether sudden or slow, is what it is meant to address: settlement that has stopped needs monitoring, while settlement that continues needs a repair that deals with its cause. Find out why the ground dropped, stop that cause, then decide whether the foundation needs new support and whether the structure should be lifted. Where the cause was a leak or a drain fault, repairing it may let the ground recover or stabilise. Where weak or collapsing ground is the cause, the repair may need concrete underpinning, piles or injection, and an engineer will say which. Where the cause is the clay swelling and shrinking with the seasons, the movement may continue after any repair, so drainage and trees remain part of the plan.

Can subsidence be fixed permanently? The honest answer depends on the cause. A repair can stop movement caused by a fixed problem, such as a leak, a washed-out footing or a loose fill, if the underlying cause is also fixed. It cannot stop the clay changing with the weather. Business pages describe their repairs as long lasting or permanent, but none of that is an independent long-term study, and the lifespan sources for injection, discussed under resin injection, disagree. Ask what a repair assumes about moisture and trees, and what happens if those change.

Insurance deserves a separate caution. Whether a home insurance policy covers subsidence, settlement or underpinning depends on the policy wording, and this page has not verified any general rule. Read the insurance policy, tell the insurer early, keep dated photographs and reports, and ask what the policy says about gradual damage and exclusions.

A sinking floor in an Adelaide home has two common causes that need different repairs. If the home is on a concrete slab, the slab or the fill beneath it may have settled, leaving a dropped corner or a hollow sound when tapped. If the home has a timber floor over a void, stumps or piers may have settled or tilted, and CSIRO notes that isolated piers affected by erosion or saturation can lose contact with the bearers they support, leaving floors bouncy. A first look under the floor or at the slab edge tells which case you have, and each sinking floor needs its own foundation repair, not a standard fix.

Lifting a concrete slab, also called slab jacking, slab lifting or concrete levelling, injects material beneath it to fill the void and raise it. Mainmark, Rectify, Adelaide Underpinning Group and others offer it for driveways, paths, garage floors and house slabs, and published pages describe it as quick and clean compared with breaking out and relaying the concrete. Levelling a slab treats the symptom, so whether it works on yours depends on why it sank. Where uncontrolled fill settled for good, lifting may suit well. A lead-generation guide on concrete levelling in South Australia makes a point worth noting: across the Adelaide plains a void under a slab can form because reactive clay shrank away from the underside through a dry summer, and the same clay swells again after winter rain. Injecting into a gap that closes by itself is a different proposition from filling a washed-out one.

The same guide suggests measuring the slab in late summer, when the ground is driest, and again in late winter. Little difference between the readings suggests permanent settlement and a better candidate for lifting. A large difference suggests the slab is cycling with the season, and material injected at the low point could push it past level when the clay returns. That reasoning comes from one platform, not from an engineer, so treat it as a good question to ask rather than a rule. A large tree within its own height of the slab, and any leaking pipe, are further reasons to fix the water first.

For commercial floors, loading docks and warehouse slabs, loads, staging and approvals are covered under commercial underpinning. For a home slab, ask how many injection points are planned, what depth, how the lift will be monitored, and whether the proposal covers steps at joints and cracks in the slab.

Wall cracks are repaired last. If the foundation is still moving, fresh filler or repointing will crack again, and a good foundation repair quote says how soon after stabilising the crack work should start. Mainmark and OB Engineering agree that cracks that have formed need their own repair once stability is achieved.

Crack repair covers a range of jobs. Hairline cracks in plaster can be filled and painted. Wider cracks in brick may need raking out and repointing, with a flexible filler where movement may recur. Step cracks through mortar beds and broken bricks may need stitching or replacement of units. Cornice gaps, skirting gaps and tile cracks are finishes, and they are usually repaired by the trade that laid them. Walls that lean or bulge are a structural matter for an engineer, not a plasterer. Brickwork around windows that has cracked can be raked out and repointed, gaps beside window frames can be sealed once movement stops, and brick that has split may need replacing.

A foundation repair business may or may not offer crack repair and finishing, and that is a question to ask. Ask who repairs the cracks and the paint, whether it is in the quote, and how long after the work it is done. Leave a few months for the ground to settle after a lift, and photograph cracks before and after so you can see whether anything reopened.

Restumping and underpinning are different repairs for different foundations. Adelaide Underpinning Group explains that restumping replaces stumps causing structural problems in a home with a floor void, while underpinning adds support to a slab or strip footing.

To tell which foundation you have, look under the floor. A house with vents around the base and stumps visible in a void is on stumps, while a house with no void and a floor at ground level is on a slab or strip footings. JR Southern describes restumping as raising or re-supporting a house, usually by jacking it up and replacing stumps, and lists lack of surface drainage, tree roots and broken underground pipes among the causes of house movement. If your home is on stumps, ask any business whether it restumps, and ask for the cause of the movement in writing, because new stumps on wet or eroded ground can settle again. How footings behave in homes that sit on strips or slabs is covered under house underpinning.

A foundation assessment is the site visit and written report that precede any repair price, and it is the stage of foundation repair most worth getting right. A thorough assessment starts with the history of the house: its age, foundation type, earlier repairs, changes to drainage and trees, and when the signs first appeared. The assessment then records the present condition, with cracks measured and dated, floor levels taken across the home, doors and windows that stick noted, and the state of the subfloor or slab edge checked.

The assessment looks next for the cause. Drains and water services are checked for leaks, downpipes and gutters are followed to where they discharge, the ground around the home is checked for pooling, and trees close to the foundation are noted. Where the soil is uncertain, the assessment may include a geotechnical investigation with soil tests, because reactive clay, collapsing soil and soft ground call for different repairs. A moisture check beside the foundation can show whether the clay is wetter or drier on one side, and a floor level survey shows how far the home has dropped.

The assessment ends with a written report: the likely cause, whether the movement is continuing, the options, a recommended repair with reasons, and the monitoring plan. Insurance is part of the picture, because an insurer may ask for an assessment report and dated photographs before considering a claim, and a later buyer may ask to see the same report. Insurance wording differs by policy, so read it, and ask the assessor whether the report can be written in a form the insurer can use. Keep every assessment, quote and invoice together, because each assessment adds to the record of what has been done to the home, and a clear assessment makes quotes comparable.

Good questions separate a considered foundation repair quote from a sales pitch. Ask who inspected the home, what the report says caused the movement and whether that cause has been fixed, which repair is proposed and why the others were rejected, how movement will be monitored, who repairs the cracks, what is excluded, and how long the work is expected to take. Ask for all of it in writing.

Have these ready before the inspection: dated photographs of cracks, floors and doors; any earlier reports, repairs or building work; the age of the home and its foundation type; the location of trees, drains, downpipes and leaks; and a note of when the signs first appeared. Having these to hand shortens the visit and sharpens the written quote.

If the signs are small and have not changed, then monitor for a season and fix any water cause first. If cracks are 5 mm or wider, or floors have dropped, then arrange an engineer's assessment. If a leak, drain fault or tree is involved, then deal with it before any repair is priced. If a quote offers one method for every home without an inspection, then ask for the engineer's reasoning before agreeing. If the home is a shop or warehouse, then read about commercial underpinning. To see who runs this site, read about us.