Summary

The Building and Construction Industry (Security of Payment) Act 2021 (WA) (SOPA) contains an effective mechanism to enable a party who has been successful in an adjudication to ‘certify’ the adjudicator’s determination and enforce it as if it was a monetary judgment made by the court.¹

Furthermore, under the SOPA, there are significant restrictions on the ability of the debtor to have that judgment set aside, because:

1. s 54(5) prohibits the debtor from bringing any cross claim or defence or challenge to the adjudicator’s determination as part of any application seeking to set aside the judgment; and
2. s 55(4) prohibits evidence used in an adjudication from being admissible before a court, arbitrator, or other person or body unless both parties consent to the admission of the evidence.

In the decision of Aaro Group Pty Ltd v Monadelphous Engineering Associates Pty Ltd [2026] WASC 143, the Court reinforced the significance of the exclusionary evidentiary provision in s 55(4) of the SOPA.²

Background

On 26 September 2025, Aaro Group Pty Ltd (Aaro) filed with the Supreme Court a Certified Copy of Determination (CCD), which determined that Monadelphous Engineering Associates Pty Ltd (Monadelphous) was required to pay Aaro over $2.58 million (First Judgment).

On 20 November 2025, Aaro obtained a debt appropriation order (DAO) requiring a third party (National Australia Bank (NAB)) to pay part of the judgment debt to Aaro (the judgment creditor) instead of Monadelphous (the judgment debtor), pursuant to which NAB paid Aaro $2 million (NAB DAO). Aaro lodged an application on 9 December 2025 for a DAO addressed to Westpac Banking Corporation but as at the date of the current decision, no DAO had been made (Westpac DAO).

Aaro filed a further CCD against Monadelphous on 9 December 2025 for $709,601.88 (Second Judgment).

Also on 9 December 2025, Monadelphous commenced separate Supreme Court proceedings against Aaro alleging breach of contract, seeking damages in the region of $18m and, amongst other things, restitution under s 55(3) of the SOPA for amounts paid by Monadelphous to Aaro. On 21 December 2025, Monadelphous applied under s 15 CJEA for orders that both judgments be suspended, the NAB DAO be set aside and the Westpac DAO be refused.

Two legal questions arose:

1. Whether ‘special circumstances’ existed to justify suspension of the judgments under s 15 CJEA.³
2. Whether evidence in and related to the adjudication process was admissible, given s 55(4) SOPA, which restricts use of “[e]vidence of anything lawfully said or done in the course of an adjudication”.⁴

The special circumstances contended by Monadelphous were, in summary, that: Aaro fundamentally failed to perform the work; an administrative error by Monadelphous prevented it from properly defending the adjudication; Monadelphous’ breach of contract claim far exceeds the judgment debts; and if Monadelphous succeeds in that claim, Aaro may be unable to satisfy the resulting judgment.

Admissibility under s 55(4) of the SOPA

The admissibility issue arose in relation to the 778-page Deetlefs Affidavit filed by Monadelphous in support of its application. Monadelphous relied heavily on this affidavit in support of its contention that ‘special circumstances’⁵ existed for the purpose of s 15 CJEA.

Aaro did not previously consent to admission of any adjudication material in the Supreme Court and raised a number of objections to the affidavit material being admitted in the current application.

Both parties relied on the decision of Pritchard J in Cape Range Electrical Contractors Pty Ltd v Austral Construction Pty Ltd [2012] WASC 304 (Cape Range) (considering the Construction Contracts (Former Provisions Act) Act 2004 (WA)). Her Honour held that the use of “anything said or done in an adjudication” was prohibited in proceedings before a court or arbitrator, which is dealing with the merits of the substantive dispute between the parties. This was confirmed in Grounded Construction Group Pty Ltd v KW Civil & Construction Pty Ltd (Grounded Construction)⁶, where it was held that evidence adduced in an adjudication will be excluded from proceedings engaging in the merits of the dispute. (See our previous article on Grounded Construction here).

Principal Registrar Griffin in Aaro found that Monadelphous sought to engage in the merits of the underlying construction dispute in support of the suspension orders sought, essentially challenging the adjudicator’s determination. The Principal Registrar held that this required consideration of the substantive dispute between the parties, which is precisely the type of inquiry that s 55(4) seeks to prevent.

This is consistent with Grounded, in which Lundberg J similarly held that adjudication material was inadmissible where relied upon to support or challenge the merits of the competing claims. However, in Grounded, Lundberg J went on to assess the plaintiff’s offsetting claims on the basis of fresh affidavit evidence and contemporaneous business records, accepting the liquidated damages and backcharges claims as true and genuine for the purpose of s 459H of the Corporations Act 2001 (Cth), and indicated that he would have ordered the statutory demand to be varied to reflect the plaintiff’s offsetting claims for liquidated damages and backcharges (notwithstanding that those claims had been the subject of the adjudication and had been rejected by the adjudicator).

In Aaro, Principal Registrar Griffin accepted that a stay of a judgment resulting from an adjudication would be appropriate where it is certain (or almost certain) that the principal will suffer irreparable prejudice because of a risk that the contractor will be unable to repay the adjudicated sum if ordered to do so. However, once the adjudication material was excluded by operation of s 55(4) of the SOPA (and other evidence was also largely inadmissible as hearsay or opinion), Principal Registrar Griffin did not consider sufficient evidence of special circumstances existed for a suspension order to be made, nor that there was sufficient evidence to establish that Aaro did not have the ability to repay the adjudicated sum.

These cases support the intent of s 55(4) of the SOPA to prevent parties from effectively reopening the adjudication by introducing material that goes to the correctness of the outcome, and the broader intention of the SOPA to preserve the ‘lifeblood of cash’.⁷ As the SOPA adjudication process is by its very nature conducted expeditiously, it is not intended to be subject to the same evidentiary standards as proceedings before the courts, which is consistent with evidence of things said or done during that process being inadmissible outside of it.

Decision

The Court dismissed Monadelphous’ application, with the result that the judgments were not suspended, the enforcement steps remained valid, and Monadelphous was ordered to pay costs.

In refusing the application, the Court found that Monadelphous had not established by admissible evidence that ‘special circumstances’ existed. The inability to rely on adjudication material significantly limited Monadelphous’ ability to demonstrate irreparable prejudice required to justify suspension of the judgments, reinforcing the high threshold imposed by s 15 CJEA.

Key takeaways

1. National approach The express evidentiary prohibition in s 55(4) represents a robust position in WA, bringing it in line with a consistent underlying policy across Australia that adjudication outcomes are not intended to be relitigated through enforcement proceedings. Rather, the court will consider evidence afresh where an adjudication ultimately gives rise to substantive court proceedings.
2. Clarification of s 55(4) SOPA’s Reach
   The decision confirms in WA that adjudication material adduced in a suspension application that engages with the merits of the underlying dispute will ordinarily be inadmissible under s 55(4).
3. SOPA’s ‘Pay now, argue later’ policy
   The decision powerfully reinforces the legislative purpose of the SOPA by holding that the s 55(4) evidentiary bar applies broadly. It demonstrates that the WA courts are developing a robust and protective approach to the enforcement of SOPA determinations, consistent with the prevailing national philosophy.
4. Practical implications
   Parties resisting enforcement should not frame any application for suspension around the merits of the adjudication. Adjudication material is likely always inadmissible under s 55(4).⁸ Rather, parties should discharge the onus on them to demonstrate special circumstances by admissible evidence. Grounded Construction confirms that parties will not be left without any evidence due to s 55(4) – they may still adduce fresh evidence specifically prepared for the court proceedings.

This article was written by Natasha Breach, Partner, Michael Harris, Special Counsel, and Emily Graham, Solicitor. 

¹Building and Construction Industry (Security of Payment) Act 2021 (WA), ss 53(1), 54, (SOPA); Enforcement may occur under the Civil Judgments Enforcement Act 2004 (WA).

²Aaro Group Pty Ltd v Monadelphous Engineering Associates Pty Ltd [2026] WASC 143, 27.

³Ibid, 9.

⁴Ibid.

⁵Ibid, 17.

⁶Grounded Construction Group Pty Ltd v KW Civil & Construction Pty Ltd [2025] WASC 307.

⁷Probuild v Shade [2018] HCA 4, 40.

⁸SOPA (n 1), 55(4); in Aaro, five of Monadelphous’s adjudication expert reports were excluded.