The fire was reported around 11:00 a.m. on Washington Court in East Windsor.
Firefighters arrived to see flames coming from the roof.
The entire second floor of the home was soon fully engulfed and sustained heavy damage.
Police say one resident was home at the time. That person escaped unharmed.
A firefighter from East Windsor Volunteer Fire Company #2 was taken the University Medical Center of Princeton at Plainsboro to be treated for smoke inhalation.
Investigators are working to determine what sparked the blaze.