Kingston fire crews were called to a small apartment building on Sydenham Street on Friday evening.
Upon arriving at the scene, officials say they could see flames on the third-storey deck.
Authorities said the fire originated in a planter on the porch and then caused some of the deck to catch fire.
Officials say the unit where the fire started was vacant and that no one was hurt in the incident.
The total cost of damages is still undetermined.