An early-morning fire that started in a vacant three-decker house at 52 Woolson St. in Mattapan turned into a three-alarm incident impacting three buildings on Monday. The fire burned through the rear porches and the roof before spreading to the 56 Woolson St., where it displaced 13 people.

According to a Boston Fire account, “An aggressive interior and exterior attack helped to stop the fire from spreading to third building, but the extreme heat melted the siding at 20 Sutton [St. in] Mattapan.”

The building where the fire started was under construction, according to BFD, which is investigating the cause. One firefighter was transported to a Boston hospital with “minor injuries,” according to the department.