The fire at 555 Belfast Road in Camden damaged half the house, making it unlivable without significant renovations, Fire Chief Chris Farley said.
Investigators returned to the scene Sunday but Farley said they are quote "pretty confident" lightning sparked the fire, through they are not sure where it hit the home.
The fire was reported after 6 p.m.
The homeowners were outside when firefighters arrived and said it felt like lightning hit their home.
The damaged area of the home included the bedrooms. Farley says the homeowners have a place to stay.
A Rockport firefighter was injured when debris dropped on his head. He was treated and released at a hospital.