The two-alarm fire was reported at 2:40 p.m. along Westwick Road, just north of U.S. 2.
Crews arrived to find a 5,000-square-foot rambler in flames, Snohomish Fire Chief Ron Simmons said.
The house had a long driveway, and firefighters had trouble getting water to the site, he said.
The people who lived there were home when the fire broke out and called 911. They were unhurt.
Several firefighters suffered heat exhaustion on scene but were OK, the chief said.
The cause of the fire remains under investigation but appears to be accidental.
Crews also responded from Lake Stevens, Monroe, Clearview, Everett and Gold Bar. Fire District 1 teams were sent to cover 911 calls in the city of Snohomish, Simmons said.
A sheriff's helicopter team initially was asked to drop water from above, but that was called off due to uncertain conditions.
Firefighters and deputies closed roads in the area. Crews remained on scene into the evening.
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