The roof of the Coast Fraser Tower was engulfed in flames during the May 25 fire. (Sue Glowach/CBC)

The Northwest Territories' fire marshal is set to reveal how a fire started at a downtown Yellowknife highrise building last week.

The fire marshal's office has scheduled a news conference for Wednesday morning to discuss its investigation of the May 25 fire, which damaged the roof of the Coast Fraser Tower on 52nd Street.

The 14-storey hotel and apartment building was evacuated, and guests and tenants have been in temporary accommodations since then. It is not clear when they will be able to return to the building.

Officials with Coast Hotels and Resorts, which owns the building, have said the 14th floor has extensive damage. The 12th and 13th floors have smoke and water damage, while the next few floors below have water damage only.

Sprinklers could've helped: deputy chief

CBC News has since learned that the tower had no sprinkler system at the time of the blaze.

Fire officials said the ladders that firefighters use do not reach beyond six storeys, so a helicopter from Great Slave Helicopters was used to dump water onto the fire.

Gerda Groothuizen, Yellowknife's deputy fire chief, said a sprinkler system could have prevented some of the damage on the 14th floor.

"If there had been sprinklers there, it could have held the fire so that firefighters could have gotten control over it and then the roof wouldn't have burned through," she told CBC News on Tuesday.

"However, on the outside of the building, sprinklers wouldn't have touched it on the outside, so it would have eventually burned through to that point."

Groothuizen said the building was constructed before sprinklers were required. The building did have an alarm system, which went off during last week's fire, so occupants were alerted, she added.

The rest of Yellowknife's highrise buildings have sprinkler systems, Groothuizen said.