The blaze on Bratton Valley Road in the Jamul area erupted shortly before 3 p.m., according to Cal Fire.
Though the flames ravaged much of the two-story house, crews apparently were able to save enough of it to keep it from being a total loss, said Kendal Bortisser, a fire captain with the state agency. They were still dousing hot spots 2 1/2 hours after the start of the blaze, which also charred a small patch of nearby brush.
The cause of the fire was under investigation. No residents were home when it began spreading, Bortisser said.
No injuries were reported.