Fire investigators say the blaze which destroyed the Aardman Animations warehouse on 10 October was caused by an electrical fault.
The warehouse contained Aardman Animations' archive
They believe a faulty CCTV system or water heater was to blame for the fire which destroyed the entire collection of Wallace and Gromit props and models.
Firefighters spent several days damping down the remains of the building.
The warehouse contained a collection built up over 30 years and included props, models, scenery and awards.
The two-month investigation found the fire had started accidentally in a ground-floor office in the Grade-II listed building.
An Avon Fire and Rescue spokesman said: "Despite the devastation we saw that day, the investigation has been able to pinpoint the fire to an office on the ground floor of the building.
"The cause of the fire was an electrical fault with an appliance. Arson has been ruled out."