The workers died on the spot after a portion of a roof came crashing down on them when they were welding it at a petrol pump in Gabtoli in Niamatpur Upazila, said Police Inspector Md Rafiqul Islam.
Police identified the dead as 40-year-old Anisur Rahman and 25-year-old Sujan Hossain.
The injured, Sanaul Hoque, Mainul Islam, Mithun Hossain and Mainul Hossain, were rescued by locals and taken to Rajshahi Medical College Hospital.