The blaze was reported about 8 p.m. at the home of Tom and Kelly Opatz at 1008 Malaga Ct. in the upper Vintage Heights section of Pleasanton.
Livermore/Pleasanton firefighters at the scene said the fire started in the fireplace and burned through part of the chimney wall's lining, catching the attic and parts of the home's second floor on fire.
At least six fire trucks, three police cars and a paramedic responded to the blaze, which required firefighters to rip out part of the home's rear roof to reach the flames.
The homeowner and a neighbor were out for a walk when the fire occurred.
No estimate of damages was available.