dads current house is a 1-1/2 story house in MN. 2nd floor has knee wall front/rear. common design feature. found out rafters are 2x4. he put on dormer and wanted to raise rear roof and inspector told him no. so he had to tear off rear roof and build up with larger lumber. front of house is untouched. house was built around 1950. does that sound standard or common for that era in MN?