What egress windows in Louisville involve
Cutting the block or poured wall, setting a header, installing the unit, then excavating outside for a well. Cutting a foundation wall is structural, so it gets done with the load supported and it goes through Louisville Metro Construction Review. Anyone offering to skip the permit is offering you a problem at resale.
Net clear opening is the number that catches people. It means the hole a person can actually climb through with the sash fully open, which is always smaller than the window you bought. A casement gives you nearly the whole frame; a single-hung gives you half.