EDMONTON -- A massive fire that caused the collapse of a 31-suite apartment building in northwest Edmonton caused $6 million in damages, investigators say.

The damages stemming from the April 8 blaze consist of $4.3 million in damage to the structure and $1.7 million in damage to the contents inside of it.

The update came Monday at the end of an investigation into the cause of the fire, which was found to be improperly discarded smoking materials.

"This was a devastating fire and one that was 100 per cent preventable," Edmonton Fire Rescue Services said in a statement.

"Fires in multi-family buildings often originate on balconies due to the improper disposal of smoking materials. These fires are able to spread quickly and undetected between units due to wind, lack of sprinkler system and lack of fire alarm systems on balconies."

It took crews six hours to get the fire under control, and eight hours in total to fully put it out.

About 50 people were displaced. There were no injuries, thanks in part to neighbouring residents who helped evacuate the complex.