The St. Joseph Fire Department was called to 1915 Alabama Street around 3:45 p.m. on Sunday.
The homeowner said he was burning leaves in the backyard, and thought he put the fire out before he left.
Firefighters said the fire started in the shed, spread to the garage, then on to the back side of the home.
One person was in the house at the time, but no injuries were reported.
"We still have an investigation to do. The garage, the detached garage, that was fully engulfed, it going to take a while to get all that out because it's on the ground now," said Russell Moore.
The homeowner believes the strong winds may have been the cause of the fire.