Ottawa Fire Services said a fire at 304 Cumberland Street in the Byward Market area started when someone threw a cigarette butt into a planter pot on a rooftop patio.
The building contained residential and commercial units, some of which sustained some fire and operational damage.
Overall damage is estimated at $150,000.
Firefighters completed extensive salvage operations in the units to minimize damage. Crews also removed certain items as a precaution.
Four people were displaced by the incident. The Salvation Army and Red Cross have been assisting those impacted by the fire.
Fire officials would like to remind residents that smoking materials should always be placed in sturdy noncombustible containers that are wind resistant and never in recycling containers, dumpsters, planter pots or mulch.