House Underpinning Adelaide: Signs, Causes and What a Home Job Involves

• What it fixes: a home footing that has lost support, so the walls and floors above it stop dropping or tilting. House underpinning gives that footing a deeper or wider base.
• Why a home moves: the clay under the house swells and shrinks with moisture, and the edges of the home react before the middle, which is why underpinning is often a response to weather and water.
• What to look for: stepped or diagonal cracks in brickwork, sticking doors and windows, floors that dish, dome or slope, and gaps at ceilings and cornices.
• Construction matters: solid brick shows damage early, while brick veneer and timber frames tolerate more movement before any underpinning is needed.
• A residential job: staged underpinning around the home, with access, services, the garden and the neighbours planned before the first dig.
• Neighbours: underpinning that affects the stability of the land next door brings a notice period under South Australian law.
• Where to begin: a few photos and a short note about the home are enough to start a quote.

Underpinning a house means giving its footings a deeper or wider base, so the walls they carry rest on firmer ground. The underpinning work happens beneath and beside the existing footings while the home stays standing above, and a house that has been underpinned should stop moving where it moved before. Anyone who wants to underpin a house in Adelaide will be asked for photos first, but the structural engineer's report should come before any quote.

In a home, three things set the job apart from underpinning other buildings. The loads are modest, so the support points are smaller than a warehouse needs. The footings are often shallow, because many older homes were built before the behaviour of clay was understood. And the people who use the building are usually the owners, who may live in it while the underpinning goes on.

Residential underpinning Adelaide owners arrange is also tied to the ground under their street. The same block can have clay on one side and firmer soil on the other, which is why a structural engineer's report matters more than a rule of thumb. The underpinning Adelaide overview explains the repair in general; this page stays with the home.

CSIRO's Building Technology File 18 describes what happens as reactive clay under a house takes in and gives up water, and the sequence is more orderly than most owners expect. A house whose footing has been underpinned stops following this cycle at the footing that failed, and an Adelaide home on reactive clay can still follow it at every other footing.

Wet spell. Moisture reaches the outer edge of the home first, so the exposed outer footings lift before the inner ones. CSIRO says this tends to give a dished effect, because the outside of the house sits higher than the middle, which is a common pattern on reactive clay. The first symptom, long before anyone thinks of underpinning, may be a floor that looks slightly dished, doors that bind on the floor or the door head, and small cracks in cornice mitres.

Moisture spreads inwards. As water reaches the middle of the footprint, the inner footings rise. If the spread is roughly even the symptoms may fade for a while. More often it is uneven, and in a home with timber floors on bearers and joists the isolated piers rise more easily than the footings under walls, which creates doming.

Dry spell. The outer footings fall first, starting where the sun is strongest. The doming is accentuated, some cracks close and others open, and roof lines may turn convex.

Where it begins. CSIRO adds that swelling usually starts at the uphill extreme of a house, or on the weather side where the land is flat, while shrinkage tends to start on the side where the sun's heat is greatest. That is why one corner of a home is often the first to crack, and why a structural engineer looks at the orientation of the block as well as the wall cracks.

The forces are mostly vertical, but a rigid house resists uneven movement, so they pass from one part to another and end up rotational. CSIRO notes that this complicates diagnosis, because the visible symptoms do not simply reflect the cause. A binding door is common even when the original movement was somewhere else.

A 1991 information sheet from the state's mines and energy department sorts houses into four rough classes, and they react differently when a footing moves. The sheet is old, so treat it as a guide to behaviour and not a survey of modern homes.

• Solid brick or cavity brick. The traditional form of construction in this state. It can be brittle, and the continuous brickwork over doorways, windows and arches may crack under small foundation movements. Older stone walls have little resistance to movement too.
• Articulated brick. The walls are broken into sections that can move against each other, using full-height frames or control joints, which lets a more economical footing work.
• Brick veneer. The timber or steel frame and plasterboard inside are flexible and absorb movement better, and concealed vertical joints can limit wall cracking in the outer brickwork.
• Timber or prefabricated. The most flexible, often on pads or supports that keep the structure off the ground.

CSIRO agrees that framed buildings are less likely to crack from swelling and shrinking than masonry ones. Their weak point is the isolated pier under a wall: when one falls away it can double the distance the wall has to bridge, and the strain shows up in the wall linings, especially beside a door or window.

Floor type matters too. The 1991 sheet describes shrinkage beneath timber floors, which dry the soil under them, and heave beneath concrete rafts when the moisture content of the ground rises over a long period. Heave tends to crack walls above doorways, particularly internal cross-walls. Cut-and-fill sites add a third pattern: localised settlement, a kind of uneven settlement, where part of the footing rests on rock or natural soil and part on fill. In an older home with a heritage listing, any of these patterns can mean extra care before underpinning starts. Before underpinning a stone or heritage home, ask the engineer how the existing stone and brick walls will cope with the underpinning, because thick masonry on shallow footings needs particular care, and a heritage officer may need to approve the method.

Walk around the house and inside it with a pencil and a phone. Signs of a footing problem are easier to judge together than one at a time, and a home that needs underpinning usually shows several. Underpinning a house is only worth discussing once several signs agree, and a house that was underpinned before can show them again if the cause was never fixed, because underpinned footings do not stop a leak.

• Outside walls. Stepped or diagonal cracking in the mortar beds, often running from the corners of windows and doors, and vertical wall cracks through the bricks themselves. CSIRO notes that brickwork cracks at weak points, and openings are the weakest.
• Doors. Sticking doors that bind on the floor or the door head, or on the vertical side of the frame. Binding on the side is common when the building is rotating, and the same rotation can make a window stick.
• Windows. Window frames pulled out of square, window sashes that stick or no longer close evenly, and new gaps at the sill, especially in the wall nearest a cracked corner. Several windows sticking in one wall point to one footing, and a window near a stepped crack is the first place to look.
• Floors. A sloping floor, one that has dished, or one that has domed, or a floor sloping towards one wall and sloping further after rain, or a timber floor that has turned bouncy because a pier has lost contact with its bearer.
• Ceilings and cornices. Cracks in cornice mitres and gaps between wall and ceiling, which often show before a wall crack does.
• The roof line. Dishing at the hip or ridge, or a convex line after a dry spell.
• Extensions and garages. A gap opening between an extension and the original house, or a crack where an extension meets an older home, since an extension built on newer footings can settle differently.

For the widths that separate a cosmetic wall crack from a serious one, see the damage categories under underpinning Adelaide. CSIRO says most cracking in masonry is cosmetic, so a crack by itself does not mean the house needs underpinning. Several signs in the same part of the home, getting worse, do.

Not every crack is subsidence, and the difference matters because underpinning a house is the wrong repair for several of them. Nobody should underpin a house to fix a crack that comes from a leak.

• Construction settlement. CSIRO says that when cracking comes from settlement during construction it will usually stay unchanged once the settling has stopped. A wall crack that is old and stable is a different problem from one that is growing.
• Seasonal swell and shrink. Some cracks open and close with the weather. CSIRO notes that repeated cycles can widen them, and that it is normal for cracking to stabilise once the building has the articulation it needs, although that is by no means always so. Monitoring is the sensible response.
• A leaking pipe, drain or downpipe. CSIRO's advice is blunt: when a failed water service, roof plumbing, sewer or stormwater system is moving the house, repair that system. A leak can saturate clay beneath one footing and leave the rest of the home alone, and a leak left running can undo underpinning that was done correctly.
• A tree. Roots can lift footings, and drying soil beside them can take away support. Removing a large tree can reverse the effect, as the moisture returns.
• Cosmetic movement in finishes. Hairline cracks in plaster or paint, or around a window frame, often reflect nothing happening to the footings, and no underpinning will change them.

How to tell them apart: write a date beside each end of a wall crack in pencil, then photograph it from the same spot each season, and note whether it follows the weather. If it keeps growing, cracking caused by erosion or local shear usually continues until the cause is fixed, according to CSIRO, and that is when a structural engineer's inspection is due.

How long house underpinning takes is the first thing most owners ask, and published guides disagree. None of them is a standard. Adelaide contractors' own pages give anything from a day or two for a small job with good access to a week or two for a typical home, with larger or more complicated underpinning running to several weeks. Interstate guides give fewer days for screw pile and resin underpinning and more for mass concrete, and add weeks before the work for the inspection and the quote.

The sensible reading is that how long house underpinning takes depends on the method, how much footing needs support, access around the home and the weather, and that the number that matters is the one in your written quote. Ask how long the work will take, in days or weeks, how long each stage lasts and how long to underpin a house of your size, and ask what could change it: ground that differs from the report, a service that has to be moved, or approval steps still to come.

Ask separately how long the repairs after the underpinning will take. Cracks and finishes are usually made good once movement has stopped, which can be days or weeks after the last pour. A job that takes a few days on site can still run for weeks once approvals, access and repairs are counted.

An Adelaide home is rarely far from the next one, and underpinning near a boundary can affect the ground next door. South Australian law deals with this directly.

According to the Law Handbook, where building work affects the stability of other land or premises, the building owner must serve a notice of intention on the owner of the affected land at least 20 business days before the work starts. The notice has a prescribed form, Form 1, Initial Notice to Owner of Affected Site, under section 139 of the Planning, Development and Infrastructure Act 2016. The owner must take every precaution to protect the neighbouring land and may still be responsible for damage from negligent work.

Party walls have their own rules. A party wall is a wall that separates buildings or forms part of a building and sits on the dividing line. A building owner has a right to make good, underpin or repair a defective party wall, or to raise and underpin one, but must give the adjoining owner written notice first unless that owner consents in writing. The owner must make good any damage to the adjacent premises, take all reasonable steps to protect them and cause as little inconvenience as possible.

Whether a particular job affects the stability of the neighbour's land is a question for the structural engineer and the council, not this page. Ask early, because a notice period can change the start date. A short conversation over the fence before the notice arrives usually helps.

Whether you may underpin a house in South Australia without building consent is a question for your council or a private certifier, and this page does not give a rule. Consents are lodged through the state's planning system, and the structural engineer's report is commonly part of what they ask for. Ask in writing and keep the answer.

Three pieces of paperwork matter most for an owner-occupier. The engineer's report, which every contractor should quote from. The contract, which for larger domestic jobs must be written and signed and show the builder's licence number, as set out under underpinning contractors. And any notice to a neighbour, if the work affects their land.

Heritage-listed and older homes can carry extra approval steps for underpinning. Tell the council or certifier about a listing before the underpinning is booked, not after, especially when underpinning a house with stone walls.

House underpinning stops a footing moving, but the reactive clay under the home still responds to water, and the finishes above it still show what happened.

• Cracks. Brick, plaster and cornices are repaired after the underpinning has stopped the movement, not before. Filling a wall crack that is still opening hides how it moves.
• Monitoring. Ask what will be watched, such as crack gauges or level checks, who reads them and for how long. CSIRO stresses that monitoring of cracks in walls and floors should always be treated seriously.
• Floors and doors. Doors and windows are eased or re-hung once the house has settled into its new position, and a floor that has dropped may be re-levelled as a separate step.
• Moisture. The 1991 sheet advises keeping garden beds and lawns away from walls, fixing leaks and blocked gutters at once, and laying paving at least a metre wide with a fall away from the home. Trees near a wall deserve a second look, and so does any drain close to the footings.

None of this replaces the structural engineer's advice for your site, and every Adelaide home on reactive clay can move again if the water is not managed. It is the habit that stops the next cycle of movement from starting where the last one did.

• If your Adelaide home has wall cracks that are hairline and unchanged, monitor them for a season before you spend anything on underpinning, and look at drainage and trees first.
• If a crack is growing or a door has started to bind, book an inspection and ask a structural engineer for a report on the footings before you collect quotes.
• If your home has timber floors and one area feels bouncy, ask the inspector to check the piers beneath it, because isolated piers can lose contact with their bearers.
• If you are about to build an extension onto an older home, raise the footings and any underpinning with the designer early, since a new addition can crack away from an old one.
• If you plan on underpinning a house close to a boundary, ask the structural engineer whether a notice is needed before the contractor sets a start date.
• If you are unsure which repair you need, read about foundation repair first, then request a quote for an assessment.

To get a quote for underpinning a house, photograph each crack next to a coin or ruler, then add every door, window or sloping floor that has moved. Say whether the walls are solid brick, brick veneer or timber, and whether the floor is timber or concrete. Note when the movement began, whether it follows the weather, and whether there has been a leak, a drainage repair or tree removal nearby. Mention how close the boundary is, whether the house was underpinned before and any previous engineer's report. Include your suburb and contact details. We reply with a next step: a visit, a request for more detail, or advice that a different repair suits the home. You can enquire through the form above or contact us, and about us says what happens next.