Place Montreal Trust opened on Saturday following a high rise fire behind it a day before.
The 5-alarm blaze erupted on the roof of the 30-storey building on the corner of McGill College and Ste. Catherine downtown.
Two roofers who were working on the building were taken to hospital, four more were treated at the scene.
Firefighters say they don't believe it was criminal, but an exact cause has yet to be determined.
There was thick black smoke was billowing late in the afternoon from the roof of the BellMedia building at 1800 McGill College Ave.