Fire investigators confirmed the cause through witness statements and lightning strike data from the National Weather Service.
A brick mason remodeling the home said he saw the lightning hit the home while he was on a lunch break. Nearby homeowners said they heard a big "boom" and saw a flash before the home began to shake. They saw a flash run down the chimney, and then flames coming from the basement.
Chapel Hill Fire Marshal Matt Lawrence said firefighters worked Friday afternoon to put out remaining hot spots in the ruins of the home overlooking the Chapel Hill Country Club.
The home sustained an estimated $1 million in damage.
A firefighter taken to the hospital during the fire was evaluated and released. He made a full recovery and was to return to work Saturday.
This was the second house fire caused by lightning in Chapel Hill this year. On June 30, a lightning strike to a tree ignited a fire in a nearby house at 4000 Sweeten Creek Road.