ATHOL — A pair of fires just six hours apart have rendered a single-family home at 21 Park St. uninhabitable.

None of the five residents were injured, according to Fire Chief Joseph Guarnera, but all were displaced by the fire. He noted that the Red Cross and Salvation Army are offering help to the family.

“The roof had caved in and there was heavy structural damage,” Guarnera said.

It’s unknown at this time if the two fires are related, and the causes are under investigation by Massachusetts Fire District 8, an organization of fire departments in northern Worcester County.

A chimney fire at the home was reported at around 8 p.m. on Tuesday. Guarnera said the fire was limited to the chimney and wood stove that it was connected to, and was quickly contained.

At 1:58 a.m. the following morning, a structure fire at the same address was reported, and the chief said that upon arrival, crews found heavy smoke and fire coming from the roof. This led to a third alarm being rung, and mutual aid was dispatched from Petersham, Phillipston, New Salem, Orange, Gardner, Erving, Barre, Oakham, Winchendon and Westminster.

The Hubbardston and Fitchburg fire departments provided station coverage. According to Guarnera, close to 40 firefighters responded.

“It was a great job by all companies,” the chief said. “The mutual aid is an invaluable tool.”

Guarnera said the fire was brought under control by 3:30 a.m., but one aspect made this a challenge. The building has two sets of shingles — slate shingles behind wooden shingles. The slate shingles trapped the heat within the void space — an empty area between two sets of shingles — which Guarnera said kept the fire going.

“At 3:30 (a.m.) were still chasing fire in the eaves,” said the chief.

Max Bowen can be reached at 413-930-4074 or at mbowen@atholdailynews.com.