Arvada Fire Protection District Public Information Officer Deanna Harrington said the building was empty when they arrived and no one was injured.
Firefighters were first notified about the fire around 2:15 a.m.
Firefighters said it took about 45 minutes to get the fire under control and another 45 minutes before the fire was declared out.
Both directions of 52nd Avenue between Wadsworth Boulevard and Vance Street were closed for about three hours due to the fire. All lanes were reopened just after 5 a.m.
Thefire was extensive, Harrinton said, and damage is significant. She said it appears the most extensive damage was done to the north side of the building.
Firefighters will be on scene throughout the morning investigating the cause of the fire.