The architect behind Investors Group Field says the building was never designed for winter or concerts.
In a statement of defence, Ray Wan said the owner, Triple B Stadium Inc, approved the designs and budget for a two to three-season stadium.
Investors Group Field is set to host the Grey Cup in November.
The claim also alleges access for semi-trucks at the field level for concerts was not part of the original scheme.
Triple B is suing builder Stuart Olson and Wan over drainage, cracking, and insulation issues that have plagued the stadium.
None of the allegations have been proven in court.
