Fire investigators determined the cause of the fire on Ridgeway Road in Bracebridge Heath on Wednesday.
Nine crews attended the property on the road which backs on to Redhall Farm as a fire spread through the roof.
No one was injured in the fire.
On Friday, August 17, Lincolnshire Fire and Rescue said the fire started in hearth of the house next door.
It then spread through a void in the chimney breast, igniting the dormer window and rafters, which then spread to the roof.