Does Your House Need Underpinning? When It Is Necessary and When It Is Not

Most visible damage to a house does not prove that underpinning is needed. Underpinning is justified only once a diagnosis has established which movement mechanism is at work and what load path the footing actually requires.

That sequence gets reversed constantly. A homeowner sees a stepped crack, calls a contractor, and receives a quote for pins before anyone has measured the floor, tested the soil, or asked why the footing moved. Sometimes the footing has not failed at all. Sometimes it has moved upward, in which case pinning it is the wrong direction of intervention entirely.

Underpinning is permanent and expensive, and done for the wrong reason it creates cracking of its own. It earns its place in a small number of clearly diagnosed situations. This article sets out which ones, which methods suit which ground, what evidence you should demand before signing anything, and what the permit position is in each of the six states and territories MFS Engineering works in.

Start here: the direct answers

Your situation	Answer	What you should do next
Cracking has appeared, no investigation has been done	Not yet. Nothing about a crack, on its own, establishes that a footing has lost bearing.	Commission a forensic structural investigation before accepting any underpinning proposal.
Investigation confirms settlement and identifies a removable cause (leaking pipe, failed drainage, a tree that can be managed)	No, or not yet. Remove the cause first and re-measure.	Fix the cause, then monitor and re-survey before deciding whether residual movement warrants intervention.
Investigation confirms bearing failure and the foundation soil’s bearing capacity cannot be restored	Yes. This is the situation underpinning exists for.	Engineered design, correct depth set by the diagnosed cause, permit obtained, temporary works planned.
Investigation confirms heave, meaning the footing has moved upward	No. Underpinning does not correct upward soil movement.	Address the moisture source and allow the footing to settle back. Pinning it can prevent that recovery.
Floors are out of level, cracking is not progressive	Not yet. A floor level survey measures shape. It does not diagnose cause.	Pair the survey with a cause investigation before treating the shape as a defect requiring underpinning.
A contractor has recommended underpinning after a free visual inspection, with no level survey and no soil data	No. There is no diagnosis on the table to justify it.	Obtain an independent forensic assessment. The section “Ten questions” below gives you the checklist.
Heritage or bluestone-footed building	It depends on the assessed heritage significance and the diagnosed mechanism.	In Victoria, significance assessment first. Elsewhere, confirm the heritage pathway with the relevant authority.

What underpinning actually does

Two words get used interchangeably and should not be. The footing is the structural element that spreads the building’s load. The foundation is the ground carrying that footing. Underpinning is work on the footing, undertaken because of a problem in the foundation.

What it does is narrow. It changes where a footing’s load goes, either by extending the footing deeper or by installing new elements that carry the load to a stratum able to hold it.

What it does not do gets less attention. Underpinning does not repair cracks. It does not fix a drainage problem. It does not remove a tree or stop a pipe leaking. It does not re-level a floor unless the method chosen is specifically designed and controlled to lift, which is a separate engineering decision with its own risks. If the movement was driven by seasonal moisture change in reactive clay, underpinning one part of the building does not stop the rest of the clay moving.

Three interventions are routinely conflated in quotes homeowners receive:

• Stabilisation stops further vertical movement by transferring load to competent ground.
• Re-levelling goes further and lifts a settled portion back toward its original position. Not every method can do that, and lifting masonry brings its own cracking risk.
• Cosmetic repair covers crack stitching, repointing and patching. It belongs at the end of the job and achieves nothing if done first.

A proposal that does not say which of the three it is buying you is not a proposal you can evaluate. For background on how footing type affects all of this, see MFS’s article on the different types of footings used in Australian construction.

When the answer is yes

Underpinning is the correct answer when the foundation soil can no longer carry the load and its capacity cannot practically be restored. In practice that means:

• Bearing failure confirmed by investigation, where the soil beneath the footing has lost capacity and restoring it is not feasible.
• A footing founded on unsuitable material, such as uncontrolled fill or a stratum that has consolidated and will not recover.
• A footing never designed for the depth or load now required, whether because the original design was inadequate or because the building’s loading has changed.
• Loss of support from adjacent works, where nearby excavation or new construction has undermined the footing.

What these have in common is that the footing can no longer get what it needs from the ground it currently sits on, and nothing in the situation will correct itself. The load has to find another path. That is the only job underpinning does well.

When the answer is no, or not yet

• The cause has not been identified. This is the single most common reason a recommendation is premature. Without a mechanism, the depth cannot be set, the extent cannot be defined, and there is no way to predict whether the work will help.
• The movement is heave. Covered in full below.
• The cause is removable. A pressurised leak, a blocked or absent stormwater connection, a tree whose moisture demand can be managed. Deal with the cause and much of the movement resolves without structural work.
• The movement is seasonal and reversible. Reactive clay shrinks as it dries and swells as it wets. That cyclical movement is normal behaviour for a site classified under AS 2870-2011, and cracking that opens in summer and closes in winter is not evidence of bearing failure.
• The damage is cosmetic and not progressing. Cracks that have not changed in years are a repair problem, not a footing problem.

There is a further reason for caution that applies even when the diagnosis supports intervention. Residential underpinning is often partial, because the diagnosed movement is commonly localised and treating an entire house is rarely justified. Partial underpinning creates a stiffness discontinuity: one section now sits on competent ground and moves very little, while the adjacent section keeps responding to seasonal moisture change. The transition between them is where new cracking tends to appear. This risk is real, it is well understood, and it needs assessing in a risk-versus-benefit study before work proceeds rather than discovering it afterwards.

And it cannot be undone. Once the pins are in, they are in.

Why settlement and heave require opposite thinking

Get this one wrong and everything downstream is wrong.

Settlement and heave are opposite mechanisms and require opposite responses. Underpinning addresses loss of bearing support. It does not correct heave, and applying it to a heaving zone while the rest of the building continues to move with moisture makes differential movement worse.

The reasoning is straightforward once the mechanism is clear. In settlement, the ground beneath the footing has given way and the footing has gone down with it; transferring load to a deeper competent stratum solves that. In heave, reactive soil has taken up moisture and expanded, pushing the footing upward. The footing has not lost support. It has been given too much, in the wrong direction. Pinning it to a deeper stratum does not lower it. What it does is anchor that portion of the building while the surrounding soil continues its moisture cycle, locking in the differential.

Where the correct response to heave is to address the moisture source and allow the ground and footing to recover, underpinning can physically prevent that recovery.

Recommending underpinning for a heaved footing is not a marginal judgement call. It is the wrong intervention for the diagnosed mechanism, and it appears in quotes more often than it should.

Distinguishing the two is investigation work, not a visual assessment. A floor level survey establishes the shape the building is currently in. It does not tell you whether that shape resulted from downward or upward movement, or when. Cause diagnosis requires the survey plus site history, drainage and plumbing condition, vegetation, soil data, and where available, repeat measurements over time. MFS’s case study on soil heave affecting a backyard spa shows how the distinction plays out on a real site.

Method selection

There is no best method. There is a method that suits the diagnosed mechanism, the ground profile, the access available, and the load being transferred.

Mass concrete underpinning proceeds in alternating bays so the wall above is never left spanning more than it can carry. Each bay is excavated, filled with concrete, and connected to the underside of the existing footing with a dry-pack or grout layer once the concrete has cured and shrunk.

Method	What it does	Suits	Does not suit	Notes
Mass concrete (traditional)	Excavates below the existing footing in a hit-and-miss sequence and backfills each bay with concrete. The result is a deeper footing on the same line.	Shallow footings, localised movement, sites where machine access is limited.	Deep competent strata, sites where prolonged excavation beside a loaded footing is unacceptable.	Labour-intensive, slow and disruptive. Carries the highest temporary-works risk of the methods listed, because it involves open excavation directly beneath a loaded footing.
Screw / helical pile	Steel piles with helical plates are screwed into a competent stratum. The footing load is transferred to those piles either through brackets fixed to the existing footing or through a reinforced concrete pile cap cast beneath it, depending on what the design requires.	Sites with an identifiable competent bearing stratum at reachable depth; restricted access.	Ground with no reliable bearing stratum within the pile’s practical reach, or obstructed ground.	Installation torque provides an on-site indication of capacity. The pile itself is installed by applying torque rather than by digging, which avoids the extensive excavation mass concrete underpinning requires. Exposing the existing footing to form that connection, whichever type the design calls for, still needs a small, localised excavation, so “no excavation at all” is not accurate. The reduced excavation and lower concrete volume compared with mass concrete underpinning also give this method a smaller material and site-disturbance footprint.
Mini-pile / micropile	Small-diameter piles are drilled or driven to a competent stratum and anchored there. Load then bypasses the moving ground above.	Restricted-access sites, and cases where load must be carried below a deep influence zone such as tree-root desiccation.	Situations where the required depth has not been established by design.	Depth is design-driven, typically in the range of roughly 2 to 10 metres depending on ground profile, design loads and testing. AS 2159-2009 sets the design and installation process, not a fixed depth. Any proposal quoting a standard depth without design justification should be questioned.
Beam and base	Mass concrete bases sit at intervals beneath a load-bearing wall. Reinforced concrete beams span between them and carry the wall load onto the bases.	Continuous load-bearing masonry walls where bases can be placed at intervals rather than continuously.	Isolated pad footings, or walls that cannot tolerate the temporary spans involved.	Less concrete volume than continuous mass concrete for the same wall length, at the cost of a more involved reinforced design.
Resin injection	Expanding polyurethane resin is injected into the ground to improve or densify it, and in some applications to lift.	Ground improvement where the design accepts the current evidence base, and where minimal disturbance is a genuine constraint.	Any case being sold as structural underpinning without a design demonstrating the required load path.	Resin injection is a ground-improvement technique. It is not automatically structural underpinning. On reactive clay the resin is normally injected into soil that has already dried and shrunk. Published testing indicates that injected resin can delay that soil’s rehydration rather than prevent it. Evidence about long-term performance across a full moisture cycle remains limited, so the design should state what behaviour it assumes. See MFS’s explainer on resin injection ground engineering, and the case study on a resin injection stabilisation failure.

The tree case illustrates why depth cannot be a default. Tree-related desiccation in reactive clay can extend to approximately three metres, as documented in a monitored Melbourne study, and the actual active depth has to be established for the site rather than assumed. If the diagnosed cause is a tree that is being retained, pins founded at 1.5 metres may remain inside the active moisture zone and may therefore continue moving with it. The depth follows the mechanism. Set it from a price list and the pins can end up in moving ground.

Ten questions to ask before you accept an underpinning proposal

If a contractor or engineer cannot answer these, the proposal is not ready to sign.

1. What movement mechanism has been diagnosed, settlement or heave or something else, and what measurements support that conclusion?
2. What caused it, and can that cause be removed or managed instead?
3. Where is the floor level survey, when was it taken, and is there more than one set of readings separated in time?
4. What does the soil investigation say about bearing capacity at the proposed founding depth, not just at the surface?
5. What site classification applies under AS 2870-2011, and how does the reactivity of this site change the recommendation?
6. What depth are the pins or piles, and what specific evidence sets that depth?
7. Which portion of the building is being underpinned, what happens at the boundary with the portion that is not, and has that differential stiffness risk been assessed?
8. Who has produced the engineered design, and under what professional registration in this state?
9. What permit or approval applies here, and who is responsible for obtaining it?
10. What is the temporary works plan for excavating beneath a loaded footing, and who has prepared it?

Question 7 is the one most often skipped, and it is where the new cracking comes from.

Construction risk during the work

Excavating beneath an existing loaded footing is a temporary-works problem in its own right, independent of whether the permanent design is correct. The excavation is unsupported ground beneath a structure that is currently relying on it. Excavation work in Australia is governed by Safe Work Australia’s Model Code of Practice: Excavation Work, and underpinning excavation sits squarely within its scope.

This is the engineering reason behind the hit-and-miss sequencing used in mass concrete underpinning. Bays are opened alternately so that the unsupported length beneath the footing at any moment stays within what the wall above can span. A contractor who opens a continuous trench beneath a footing to save time is no longer building what was designed.

Ask who has prepared the sequence and the excavation support design, and confirm it is a named, qualified person rather than site practice.

Historic and heritage buildings

Heritage buildings introduce two constraints at once: footing forms that behave differently from modern construction, and statutory limits on what may be altered.

Bluestone and other early masonry footings are not simply older versions of a modern strip footing. They are often shallow, wide, of variable construction quality, and bedded on material that was never characterised. Assumptions carried over from contemporary residential work do not transfer, which is why Victorian and Edwardian houses need to be assessed on their own terms.

In Victoria specifically, buildings on the Victorian Heritage Register require significance assessment before structural change. Heritage Victoria’s principles for considering changes to places in the Victorian Heritage Register set out that framework. That citation is Victoria-specific and should not be read across to the other jurisdictions; each has its own heritage authority and its own consent pathway.

Minimally invasive techniques, including resin injection, are frequently proposed for heritage buildings on the basis that they avoid excavation adjacent to fragile footings. That is a legitimate reason to consider them. It is not, by itself, a reason to accept one. The classification point above still applies: ground improvement and structural underpinning are different things, and a heritage building needs the design to demonstrate which one it is receiving. On a reactive clay site, the rehydration behaviour described in the method table applies here as well, and the design should say what long-term behaviour it assumes.

Permits and professional responsibility, state by state

Underpinning is regulated building work in every one of the six states and territories MFS Engineering operates in. The mechanism differs by jurisdiction, so the answer to “do I need a permit” differs too. All six name underpinning somewhere in their own rules, but the instrument varies, and so does what it triggers.

Victoria. Underpinning is expressly excluded from the general repair-and-maintenance permit exemption and normally requires a building permit. The Victorian Building Authority’s practice note BP-01, When is a building permit required, lists underpinning and replacement of footings among the works that fall outside that exemption.

Queensland. Underpinning is defined building work under the Building Act 1975 and normally requires a development permit for building work, supported by an engineered design. Section 5 of the Act defines building work to include underpinning, whether by vertical or lateral support. Residential building work over $3,300 generally also requires QBCC home warranty cover, calculated on materials, labour and GST combined, though the scheme has its own definitions and exclusions. Check the specific job against the QBCC’s A to Z guide of insurable work rather than treating the dollar figure as the whole test.

New South Wales. Underpinning and piering is a separately licensed class of trade work. NSW Fair Trading requires a licence for residential building work valued above $5,000 in labour and materials including GST, and the scope of what counts as underpinning and piering is defined in Schedule 4 of the Home Building Regulation 2014.

Tasmania. Tasmania names underpinning in the legislation itself. Section 4 of the Building Act 2016 defines building work to include underpinning a building. What that triggers depends on which category the work falls into, low risk, notifiable work or permit work, and those categories are set by the Director of Building Control’s determination on categories of building and demolition work. Structural, load-bearing work does not sit in the low-risk category, so expect a building surveyor to be involved. Confirm the category with a building surveyor before work starts.

South Australia. South Australia names underpinning in its licensing law rather than its consent framework. The Building Work Contractors Act 1995 includes underpinning a house in the definition of domestic building work, so the contractor must hold the appropriate licence. Whether building consent is required runs through the Planning, Development and Infrastructure Act 2016, which defines building work broadly and does not single underpinning out. Confirm the consent pathway with your council or a private certifier before work starts.

Australian Capital Territory. The ACT Building Act treats underpinning as structural building work. Section 10 specifically gives underpinning a subsiding building as an example of work involving a structural element carrying building load. Confirm the approval and certification pathway with a building certifier before work starts.

This article does not cover Western Australia or the Northern Territory.

Separately from the permit question: work of this kind requires an engineered design by an appropriately registered engineer, and registration requirements are jurisdiction-specific. Confirm the registration that applies in the state where your building sits.

Frequently asked questions

Does cracking mean my house needs underpinning?

No. Cracking is a symptom with many causes, including reversible seasonal movement in reactive clay. It establishes that something has moved. It does not establish that a footing has lost bearing.

Will underpinning stop my house cracking?

No, not as a guarantee. Underpinning changes the load path for the section it supports. If the cause of movement was not correctly identified, or if the untreated portion of the building continues to move, new cracking can appear at the boundary between underpinned and non-underpinned sections. MFS does not attach a numerical probability to that outcome, because the evidence base does not support one.

Can underpinning be reversed if it turns out to be wrong?

No. It is permanent. This is the main reason to insist on diagnosis first.

Is resin injection the same as underpinning?

Not automatically. Resin injection is a ground-improvement technique, and it becomes part of a structural solution only where a design demonstrates the required load path. On reactive clay there is one more thing worth knowing: published testing indicates that injected resin can delay the soil’s rehydration rather than prevent it. Evidence about long-term performance across a full moisture cycle remains limited, so ask what the design assumes about it.

Do I need a permit?

In Victoria, Queensland and New South Wales, yes, through the mechanisms set out above. In Tasmania, South Australia and the ACT, underpinning still falls inside the regulated building work framework, but the category and the approval pathway are set locally, so confirm them with your building surveyor or certifier before work starts.

How deep should the pins go?

As deep as the diagnosed mechanism requires. If a tree is being retained and root-related desiccation extends to around three metres on that site, pins founded above that depth may remain within the moving zone. A standard depth offered without design justification is a red flag.

Should I underpin the whole house?

Usually not, and that is not a cost decision alone. The diagnosed movement is commonly localised, so partial underpinning is the usual outcome. The consequence is a stiffness discontinuity that has to be assessed before the work starts.

Can a heaved footing be underpinned?

No, not as a treatment for heave itself. Heave and settlement require opposite responses, and underpinning a heaving zone can prevent the recovery that resolving the moisture source would otherwise allow. If a separate bearing or load-path problem exists alongside the heave, that problem needs its own engineered assessment.

Does a floor level survey tell me whether I need underpinning?

No. A floor level survey measures the shape the building is in. Diagnosis requires cause investigation alongside it. MFS’s floor level survey service is one input to a forensic investigation, not a substitute for one.

Who should assess this?

A forensic structural engineer, engaged independently of whoever would perform the remedial work. That separation matters: the party diagnosing the problem should not be the party selling the solution.

The final decision

Underpinning should follow diagnosis, not precede it.

Every recommendation in this article follows from that one rule. Establish the mechanism. Establish the cause. Establish whether that cause can be removed. Only then decide whether the load genuinely needs to be transferred somewhere else, how deep, and over what extent, with the differential stiffness risk actually assessed.

Work done in that order sometimes concludes that no underpinning is needed, and that conclusion has the same engineering value as the alternative. Work done in the reverse order produces a permanent, expensive modification founded on a guess.

If you have cracking, uneven floors, or an underpinning quote you are unsure about, MFS’s forensic structural investigation service is the starting point. Our page for homeowners and investors sets out how that process runs. Contact us to discuss your building.

About the author

Sara Khani is a Senior Forensic Structural Engineer at MFS Engineering Australia, with more than 20 years of engineering experience, approximately 15 of them in Australia. She investigates structural failures and building defects where the cause or the remedy is unresolved or disputed, and acts in rectification, multi-party building dispute and expert-witness matters.

Credentials. Sara Khani holds RPEQ registration in Queensland (RPEQ 26271), professional engineer registration in Victoria (PE0005122) and professional engineer registration in New South Wales (PRE0002683), and is listed on the Engineers Australia National Engineering Register (EA ID 4312538). She is a member of the Forensic Engineering Society of Australia, the Association of Consulting Structural Engineers Victoria (ACSEV), and the Building Dispute Practitioners’ Society.

References

• Victorian Building Authority, Practice Note BP-01: When is a building permit required. bpc.vic.gov.au
• Building Act 1975 (Qld), s 5. legislation.qld.gov.au
• Queensland Building and Construction Commission, A to Z guide of insurable work. qbcc.qld.gov.au
• NSW Fair Trading, Underpinning and piering licences. nsw.gov.au
• Building Act 2016 (Tas), s 4. legislation.tas.gov.au
• Director of Building Control (Tas), Determination: Categories of Building and Demolition Work. cbos.tas.gov.au
• Building Work Contractors Act 1995 (SA), s 3. legislation.sa.gov.au
• Building Act 2004 (ACT), ss 6 and 10. legislation.act.gov.au
• Safe Work Australia, Model Code of Practice: Excavation Work. safeworkaustralia.gov.au
• CSIRO, Foundation Maintenance and Footing Performance, 2024 edition. research.csiro.au
• Heritage Victoria, Principles for considering changes to places in the Victorian Heritage Register. heritage.vic.gov.au
• A Parametric Study of the Effect of Trees on Residential Footing Design on Expansive Soils, Geotechnical and Geological Engineering. link.springer.com
• Buzzi, O., Fityus, S. and Sloan, S.W., Use of expanding polyurethane resin to remediate expansive soil foundations, Canadian Geotechnical Journal 47(6): 623-634. doi.org
• AS 2870-2011, Residential slabs and footings, Standards Australia.
• AS 2159-2009, Piling, design and installation, Standards Australia.