Firefighters say the blaze began in the 107-year-old mansion's attic just after noon and video from Air4 showed large flames erupting from the roof.
"While we were fighting the fire, one firefighter did have ceiling material drop on him and was minorly injured," said Kyle Moore with Seattle Fire. "He was taken to Harborivew Medical Center to be checked out."
Six people inside the home when the fire began made it out safely and no one else was hurt.
Hugo Caplow was two blocks away when he saw the smoke and heard the alarms. He rushed toward the burning home.
"The flames were around 10 feet high and smoke was billowing throughout the whole roof," he said. "It was chaos... I thought the whole building was going to burn down at one point."
Bianca Raffety was among those inside the home when the fire started.
"Somebody inside smelled wood smoke and then our fire alarm went off," she said. "We came out and found the south roof on fire."
Fire investigators say workers using a grinder was what sparked the blaze. Raffety said there were people doing repair work on the gutters earlier in the morning.
The home is said to be 7,650 square feet with 13 bedrooms with an assessed value at $2.8 million. According to King County records, the home is owned by the Evergreen Land Trust and is used as a communal house.
"The purposes of Prag House are to encourage communal living as a viable alternative and to advance the growth of cooperating communities and non-polluting technologies," according to the Evergreen Land Trust website.
It's what drew Raffety to the home, a place she's lived for the past 13 years with her son.
"I really liked the idea of low impact living and having a community of people to connect with around meaningful purpose in terms of conservation," she said.
She said the fire has her feeling pretty wrecked.
"I gave birth to my son in this house, so it's really important to me," she said.
The Red Cross is helping the 13 people and dog displaced by the fire. Damage is estimated at $1 million to structure and $250,000 to contents.