The fire at 25646 Sublett Drive near Cody Road was reported just past 9:30 a.m., when neighbors spotted heavy smoke and fire coming from the single-family home, according to Hayward fire spokesman Thor Paulsen.
Firefighters found heavy smoke and fire coming from the rear of the home. Poulsen said there was a garage conversion on the home that was only accessible from the rear, making it difficult for firefighters to reach the flames.
The fire had been put out at the ground floor but had moved into the attic as of shortly after 10 a.m.
There are no injuries reported, but Poulsen said that firefighters have been unable to make a thorough search of the house and don't know yet whether anyone was inside.