The decision of Aaro Group Pty Ltd v Monadelphous Engineering Associates Pty Ltd [2026] WASC 143 confirms that material adduced in an adjudication will ordinarily be captured by s 55(4) of the Building and Construction (Security of Payment) Act 2021 (WA) (SOP Act) in any further Court proceedings where the validity of the relevant adjudication determination is not at issue.
Aaro Group Pty Ltd (Aaro) had obtained two adjudication determination against Monadelphous Engineering Associates Pty Ltd (Monadelphous) and was seeking to enforce them in the Supreme Court of Western Australia, pursuant to s 54(1) of the SOP Act. Collectively, the determinations required that Monadelphous pay Aaro approximately $3.3 million (excluding GST). The determinations were filed as court judgments, and Aaro commenced enforcement proceedings with respect to one of them.
Simultaneously, Monadelphous filed a writ with the Supreme Court, seeking restitution under s 55(3) of the SOP Act for amounts paid by Monadelphous to Aaro (Substantive Claim). Shortly after it filed its writ, Monadelphous also applied to suspend Aaro’s enforcement proceedings whilst the Substantive Claim was being heard by the Court.
Importantly, Monadelphous was not challenging the adjudicator’s jurisdiction or the validity of the determinations; rather, by asking the Court to suspend Aaro’s enforcement until its claim for restitution was determined, it was effectively inviting the Court to reconsider the merits of the underlying payment disputes before the adjudicated amount was paid.
Enforcement of a valid court judgment can only be suspended in special circumstances. Monadelphous argued that the special circumstances which would justify suspension of the enforcement proceedings were partly demonstrated by things said or done in the course of the adjudications, so the adjudication applications and materials were admissible, and the Court should have regard to them. Aaro argued that pursuant to s 55(4) of the SOP Act, the Court could not have regard to those things.
In reaching its decision, the Court considered the case of Cape Range Electrical Contractors Pty Ltd v Austral Construction Pty Ltd [2012] WASC 304 (Cape Range), as well as Grounded Construction Group Pty Ltd v KW Civil & Construction Pty Ltd [2025] WASC 307 (Grounded Construction). Although factually different (Cape Range was a decision relating to the equivalent provision under the old Construction Contracts (Former Provisions) Act 2004 (WA) and Grounded Construction related to an application to set aside a statutory demand arising out of an adjudication determination) the Court in both cases concluded that that material adduced in an adjudication is only admissible in proceedings which do not require the Court to assess the merits of the contractual dispute between the parties. In the event that the Court is required to engage in “some degree of analysis of the force or strength of an asserted claim”[1] then the adjudication materials will ordinarily be captured by s 55(4) of the SOP Act and will be inadmissible as evidence.
The Court concluded that the adjudication determinations and expert reports which Monadelphous sought to rely on were inadmissible pursuant to s 55(4) because they had been prepared for the purpose of the adjudications, and Monadelphous was not seeking to challenge the legitimacy of the determinations.
This decision confirms that section 55(4) of the SOP Act is a prohibition on the use of evidence adduced in an adjudication in proceedings before any judicial body contemplating the merits of the contractual dispute. In this regard it is similar to the Harman Obligation; it acts as a strict evidentiary barrier.
The only exceptions to the prohibition are if:
Therefore, parties should be wary of relying on affidavits, expert reports, submissions, and even determinations prepared for the purposes of an adjudication process as the basis for any claim which may require the court to consider the merits of the contractual dispute between the parties; it is entirely consistent with the purpose and object of the SOP Act that evidence of things said or done in adjudication will be inadmissible in circumstances where a court is required to engage with the merits of the underlying contractual dispute. [2]
This article was written by Belinda Wong, Partner, Briony Whyte Senior Associate and Nikita Stankoski, Lawyer Construction