The DSA report also confirms there is no effective seismic bracing for the auditorium roof, connections between the stage house roof and walls could fail in an earthquake and the proscenium arch wall is a structural weakness in an earthquake.
Sean Murray, executive director of H3, says the report reinforces the prudent decision to close the theatre.
"When we began investigations into refurbishing the theatre, the seismic strength of the building became a concern for us," Mr Murray said.
"Dunning Thornton confirmed our earlier advice the theatre needed a major seismic strengthening upgrade, and they have validated the work and cost we would need to do if Council opts to refurbish the theatre - estimated to be $20 million."
Council has undertaken a regional consultation on the future of the theatre, presenting three options for comment - to refurbish the existing Founders Theatre, to construct a new theatre, or to demolish the existing facility. More than 2000 submissions on the future of the theatre were received.
Hamilton City Council will hear from more than 50 submitters today and tomorrow who had registered to speak to the Council as part of the hearings.