I keep coming across recessed square ceiling fixtures in houses built in the 1950’s.  These are well built fixtures roughly 12″x 12″ x 7″ with an attached junction box on the outside.  Their door has a single thumb screw and glass lenses which closes tightly.

Does any one know of a retrofit to upgrade this type of fixture so it can be covered with insulation? 

I have replaced many on these units completely in the past.  They are often embedded in plaster or lath and plaster which makes removal difficult followed by plaster repair afterwards.

How about using sheet metal nibbler and mounting a new fixture inside the metal box after the guts have been removed? 

It’s easy enough to make an enclosure in the attic to box in the fixture and keep an air space around the old units, but I’m looking to added protection of high temp breaker and IC rating like the newer fixtures.

Any thoughts?