Miss the foundations data and both states block you from recovering what it would have found. New modelling from Adelaide University puts a number on how large that gap can get.
The soil report is close to the cheapest document on a residential job and it decides more money than almost any other. In Victoria and Queensland it is also the one the law says you have to have before you sign, not after.
Most builders know that second part loosely. Fewer know how hard the consequence bites. In both states, if you enter the contract without obtaining the foundations data and the site then costs more than you allowed, you cannot recover the difference from the owner. Not by variation. Not by a rise and fall clause. You wear it.
New research from Adelaide University gives a sharper sense of what that difference can be worth.
What the gap between two footing designs actually looks like
Geotechnical engineers at Adelaide University have published a study in the Journal of Rock Mechanics and Geotechnical Engineering combining several years of field observation at a site south of the city with numerical modelling of cracked and uncracked ground. Lead author Dr Bikash Devkota and senior author Associate Professor Rajibul Karim, both from the university’s School of Civil Engineering and Construction Management, ran a hypothetical stiffened raft, 15 metres by 12 metres, four long beams and five short, against different assumptions about how deep seasonal moisture movement reaches in reactive clay.
On ground with no shrinkage cracks the design needed a 300 millimetre beam depth, with two 12 millimetre bars top and bottom. Once cracks went into the model that beam moved to 550 millimetres, then 640, then 720. The external beams went from four bars to ten. Beam width stayed at 300 millimetres throughout.
The calculated ground movement behind those designs went from 70 millimetres to 126 millimetres. Under AS 2870 that is the difference between a Class H2 site, which runs from 60 to 75 millimetres, and Class E, which is anything above 75.
That is one classification step, on one hypothetical house, and it more than doubles the beam. Deeper excavation, more concrete, more steel, more time. On a real job it is the kind of number that decides whether the site works allowance holds or not.
The duty starts before the contract, not before the excavator
Victoria and Queensland put the obligation in the same place and both put it early.
Section 30 of the Victorian Domestic Building Contracts Act 1995 applies to any major domestic building contract where the work will require footings to be built or altered, or may adversely affect existing footings. Before entering into the contract, the builder must obtain foundations data for the site. The penalty is 50 penalty units, which at the value set on 1 July 2026 is about $10,455.
Queensland does the same through section 31 of Schedule 1B of the QBCC Act, for regulated contracts. Same trigger, same timing, maximum penalty 100 penalty units, about $17,270 at the value that took effect on 1 July 2026.
What is foundations data?
Foundations data is the information a builder exercising reasonable care and skill would need to prepare two things: a proper footings design for the site, and an adequate estimate of the cost of constructing those footings. It is defined that way in section 30(3) of the Victorian Domestic Building Contracts Act 1995 and in section 8 of Schedule 1B of the Queensland Building and Construction Commission Act 1991. The costing is written into the definition, not bolted on afterwards. Victoria adds that in deciding whether enough has been obtained, the builder must have regard to the relevant Standards Australia standards. The Act’s own endnote names AS 2870.
Neither state makes you pay twice for work that already exists. Both provide that data already available can be relied on where it is reasonable to do so. Queensland adds one further carve out that Victoria does not have. Where the contractor is not lawfully entitled to enter the land before entering the contract, the duty does not apply, but only if the contract also guarantees there will be no increase in the price because of the foundations data. Both limbs are required. You cannot use the access problem to defer the test and keep the right to bill for it.
The part that costs money is not the fine
The penalty is the smaller half of the exposure.
Victorian section 30(7) says that after entering the contract, a builder cannot seek an amount from the owner that is not already in the contract if that amount could reasonably have been ascertained had the builder obtained the foundations data. Queensland section 31(8) says the same thing in the same shape.
Queensland then closes the obvious escape route. Section 31(9) provides that an amount is not treated as provided for in the contract merely because the contract contains a clause allowing the price to be increased. On that reading, a rise and fall provision does not convert an unpriced site cost into a recoverable one.
You cannot use the access problem to defer the test and keep the right to bill for it.
There is a symmetrical protection running the other way. If you did obtain the data, and the extra cost genuinely could not have been established from it, both states preserve the right to claim, subject to what the contract actually allows you to claim. The law is not punishing surprises. It is punishing not looking.
Provisional sums do not fix it either
The common workaround is a provisional sum for site works, set at a round number, with the soil test to follow.
Queensland warrants against that directly. Section 26 of Schedule 1B provides that the builder warrants a provisional sum or prime cost item has been calculated with reasonable care and skill, having regard to all the information reasonably available when the contract is entered into, including information about the nature and location of the building site. Victoria carries an equivalent warranty. The site is named in the statute. A provisional sum set without looking at the site is a warranty problem before it is a pricing one.
How that plays out is familiar to anyone who has watched a job go sideways. TGB has previously reported a case where a provisional sum of $2,000 allowed for piers met a site carrying up to 1.5 metres of uncontrolled fill. The engineering came back at $35,000. The builder was not inventing the cost. The allowance had simply been set without data.
New South Wales has no equivalent duty, which is not the same as no exposure
The Home Building Act 1989 contains no foundations data provision. The current consolidation carries no reference to soil investigation at all.
That absence is worth reading precisely. A New South Wales builder has no statutory pre contract obligation of this kind and no statutory bar on recovery flowing from it. The risk does not disappear. The contract still has to allow the claim, the Australian Consumer Law still applies to how an estimate was represented, and the ordinary licensing and compliance obligations across Australia still require a footing design with a classification behind it. Victoria, Queensland and New South Wales are the three jurisdictions checked here. The other five were not, and they vary.
Why the assumption underneath all of this is under pressure
AS 2870 was published in 2011 and remains the referenced standard for residential slabs and footings under the National Construction Code. It assigns each locality a depth of design soil suction change. That figure sets the ground movement calculation, which sets the classification, which sets the footing.
The Adelaide University study modelled 3.8 metres for uncracked ground, close to the 4 metres the standard sets for the city. With cracks in the model it rose to between 5.5 and 7.3 metres. The authors are careful about the limits of the work, and nothing in the code has changed. Building ministers have paused further residential code changes, beyond essential safety and quality measures, until mid 2029.
What the research does suggest is that the range of site cost outcomes on reactive clay is wider than the standard currently assumes. Which makes the document that narrows that range, before anyone signs anything, worth considerably more than it costs.
Frequently asked questions
Before entering into the contract. Section 30 of the Domestic Building Contracts Act 1995 requires a builder to obtain foundations data for the site before entering a major domestic building contract, where the work will require footings to be constructed or altered or may adversely affect existing footings. The penalty is 50 penalty units.
In Victoria and Queensland, not if the foundations data was never obtained and the amount could reasonably have been ascertained from it. Victorian section 30(7) and Queensland Schedule 1B section 31(8) both bar recovery in that situation. Where the data was obtained and the need still could not be established from it, both states preserve the right to claim.
In Queensland, section 31(9) of Schedule 1B provides that an amount is not treated as provided for in the contract merely because the contract contains a clause allowing the price to be increased. A price increase clause on its own does not make an unpriced site cost recoverable where the foundations data duty was not met.
It is the information a builder exercising reasonable care and skill would need to prepare a proper footings design for the site and an adequate estimate of the cost of constructing those footings. It is defined in section 30(3) of the Victorian Domestic Building Contracts Act 1995 and section 8 of Schedule 1B of the Queensland Building and Construction Commission Act 1991.
The Home Building Act 1989 contains no foundations data provision and no equivalent pre contract duty. That means no statutory bar on recovery of the kind Victoria and Queensland impose, but contractual terms, the Australian Consumer Law and building approval requirements still apply.
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Last updated: 9 September 2026. Penalty unit values reflect the rates that took effect on 1 July 2026 and are reset each financial year. Statutory references reflect the Victorian Act version 093, the Queensland Act as at 1 February 2026 and the New South Wales Act as at 10 June 2026.
General information only. This article is editorial commentary for construction industry professionals and does not constitute legal, engineering or regulatory advice. Statutory obligations differ between jurisdictions and turn on the facts of each contract. Obtain your own advice before relying on any of it.
Author: TGB Editorial
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