Investigators with the Boulder Fire Department have determined that the fire at the Oak at Fourteenth restaurant last week started under the grease hood in the restaurant’s kitchen. At the time, cooks were preparing the wood-burning grill and also using the deep-fryer.

The cause of the fire has been determined as accidental.

The fire started on the first floor and traveled up through the grease ducts to the area above the second floor, under the roof. Fire investigators believe the ducts became so hot that they ignited wooden beams and the underside of the roof. Because of the ductwork in this “void” space, access was difficult for firefighters.

The fire sprinkler system in the building is credited with helping to contain the fire. Damage is estimated at more than $1 million.