Dr Reay was also criticised for not reviewing his designer's final plans.
Last year, he resigned from Ipenz and avoided its disciplinary process.
Now, Ipenz says it accepts a decision by an independent disciplinary committee to dismiss its complaint against Dr Reay's registration as a chartered professional engineer following the quakes.
The committee concluded there was no duty on Dr Reay to disclose his firm's role in the design of the CTV Building.
"He was not and could not be expected to make full and comprehensive disclosure of the buildings he or engineers associated with him had designed during the course of his career," it found.
"We are satisfied that Dr Reay's omission to disclose his role in the design of the CTV Building could not constitute a representation that he knew to be false or misleading.
Ipenz chief executive Susan Freeman-Greene today confirmed the Institution would not appeal the committee's decision.
"We accept the decision, which follows a very thorough hearing of all the facts of the case," she said.
Ms Freeman-Greene said the institution had published the committee's decision on its website because of the "very high public interest" in the hearing, including the interest of the families of the 115 people killed in the CTV building.
"In cases where a disciplinary committee dismisses a complaint, our normal procedure is not to publish the decision. However, we believe the strong public interest warrants publication in this case," she said.
In March, the Government announced that it is seeking a judicial review into the failure of Ipenz to complete an investigation into Dr Reay.
Building and Housing Minister Nick Smith said the decision to drop the probe was flawed.
"We want the decision overturned and Ipenz to complete the investigation into the professional conduct of Dr Reay's role in the design of the CTV building," he said at the time.
Ipenz has since updated its rules to "put it beyond doubt" that members cannot avoid responsibility by resigning.
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.