South Whidbey Fire/EMS personnel spent almost 10 hours on scene at a residential fire Tuesday night on Shore Avenue in Freeland. The sprawling, 7,000-foot home was unoccupied and no one was injured, according to Deputy Chief Mike Cotton.

Just before 9 p.m. Tuesday, a man on Sound View Drive, in the Useless Bay Colony area, saw what appeared to be flames across Deer Lagoon.

“It was very fortunate that the gentleman who was able to see it from a distance saw what he saw,” Cotton said.

The residence’s location is mostly composed of vacation homes, and no one nearby saw the flames, he said. The large home was almost fully engulfed in flames by the time firefighters arrived. More than 20 personnel from South Whidbey Fire responded, and because of its size, the department requested support from Central Whidbey Island Fire and Rescue and Naval Air Station Whidbey Island.

The Navy fire department has a ladder truck, Cotton said, which was used to safely reach the flames on the roof. The “extensive” wood trim also made the fire difficult to extinguish, he said.

“It had a lot of beautiful woodwork in the house,” he said.

Officials determined the cause was unintentional, but it’s still under investigation. Flames seemed to originate from an attached apartment space, Cotton said. Earlier in the day, firefighters responded to the residence because a fire alarm there went off. The alarm had been reset by the time personnel arrived, and no smoke or flames were visible inside, Cotton said.

When the fire did start, the alarm didn’t sound, according to Cotton.

About 60 percent of the home was damaged and officials are assessing the estimated cost. No other structures were impacted.