In December last year, the High Court at Wellington largely granted the attorney's application to strike out parts of Reay's statement of defence.
Reay then appealed that decision to the Court of Appeal.
In a new judgement released today, appeal judges Randerson, Wild and Winkelmann decided that Reay's appeal will be allowed.
Lawyers for both parties have agreed to lodge amended documents to the High Court setting out their respective cases.
The attorney-general must now file an amended statement of claim by no later than November 11, while Reay has until November 25 to file a statement of defence to the amended statement of claim.
"As this court has several times emphasised, judicial review is intended to be a simple and straightforward procedure enabling the court to give a decision with the requisite speed," the appeal judges said.
The Government last year announced it is looking to strengthen the regulation of engineers to "ensure they have the right knowledge, skills and competence" to design safe buildings and to hold them more accountable for substandard work.