MERCER ISLAND, Wash. -- A smoke alarm is being credited with alerting a Mercer Island family that its waterfront mansion was on fire.

The Mercer Island Fire Department responded to the fire shortly before 10 a.m. in the 3000 block of East Mercer Way Friday.

Kurt Dammeier said he had just left his home and his wife and son were still asleep. Then the house smoke detector went off.

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Dammeier said it was his wife who first realized something was wrong in the waterfront home they built 18 years ago.

“She heard he fire alarm, went upstairs, saw smoke and went and got, woke up our 14-year-old who was sleeping in. He hadn't woken up by the fire alarm,” said Dammeier.

Dammeier said they ran outside and saw smoke and within about 20 minutes the whole house was engulfed.

Chopper 7 was over the scene and showed heavy flames and smoke coming from the roof of the nearly 7,000 square foot house.

Several units were at the scene trying to get control of the flames and put the fire out for nearly two and a half hours.

Firefighters said it appears the fire started in the attic and that it was especially hot because the concrete roof tiles created an oven like effect.

Police and fire crews blocked off part of East Mercer Way for several hours to access the fire hydrants.

Dammeier owns Beecher's Cheese and Pasta & Company restaurants.

Firefighters said they may know by Monday how the fire started.