The fire at 202 Gallinas Ave. in San Rafael was reported just before noon, according to San Rafael Fire Chief Chris Gray.
Fire crews arriving on the scene found heavy smoke and fire coming from the detached garage of the one-story home, and the homeowner outside attempting to put out the fire with a garden hose, Gray said.
The garage was filled with a large number of items, which fueled the spread of the fire into the attic. The garage roof collapsed in the fire, as firefighters worked to prevent its spread to the main house.
The fire caused smoke damage to an adjacent two-story home, and also damaged an outbuilding next door. The garage and its contents were destroyed.
The homeowner suffered minor burns in the fire but refused treatment or transportation to a hospital. No other injuries were reported.
Damage was estimated at around $225,000. The fire's cause remains under investigation.
The American Red Cross has been notified to help the displaced residents.