[John Rogers]

A couple things to consider, I haven't seen anyone mention the city/county rules for window replacement. If your area is like mine they even have rules on how to scratch your ass so I would check. In our case the city of Chula Vista says as long as the building's window opening is not changed then you do not need any permits. That is why we used custom made windows that slid over the 1/2 inch protruding aluminum old window frames. We lost a tad amount of opening size but not enough to notice. Plus we gained windows we can pull out and clean both sides of the glass.

Secondly, if you do this, a sealer made for installing windows and the stuff we used was not in a Home Depot or Lowes and has a 30 year life span so I guess the high cost of it is well spent. Use a LOT and remove excess later, way better than trying to add more.