The administrative offices of the Institute of Living at 400 Washington St. in Hartford were evacuated on Tuesday when a two-alarm fire broke out.
The fire at the offices for the mental health center was reported at 11:15 a.m.
It was under control as of 11:55 a.m. but firefighters remained at the scene to check for hotspots.
Security personnel evacuated the offices and no one will be allowed back in the building on Tuesday.
The cause is not known, but officials said workers were welding in the attic.
No injuries were reported.