PITTSBURG -- A recently-sold home that was almost ready to be rented out was seriously damaged after a possible natural gas leak started a two-alarm fire Tuesday afternoon, authorities said.

No one was injured.

A 911 caller reported a loud bang and smoke coming out of the single-family house on the 100 block of School Street about 12:43 p.m., according to Contra Costa Consolidated Fire spokesman Lewis Broschard. Crews arriving on the scene reported a fire in the basement that may have spread to the main home.

The home, built in the 1920s or 1930s, uses a technique called "balloon construction," Broschard said, which does not place fire breaks in the walls. Without the breaks, fire can spread quickly up the walls -- which is what happened Tuesday, he added.

The fire spread up through the first and second floors, and into the attic. The home also had a tin roof, making it more difficult to ventilate the fire, leaving flames burning in the attic for an extended period of time, Broschard said.

Investigators believe a gas leak may have been the source of the fire, although they were still trying to determine if a nearby water heater or furnace had ignited the gas. Damage was estimated to be more than $50,000.

Contact Daniel M. Jimenez at djimenez@bayareanewsgroup.com. Follow him at Twitter.com/DMJreports.