I'm considering making a well insulated interior door and need to understand the door thickness implications for the getting a door knob. The door could be upto 3" thick - less if getting a door knob becomes a problem. I'd like to use a cheap off the shelf knob - possibly adding extensions.
A standard lockset could be inset into the face of the door, so that 95% has full insulation. You will also need to consider hinge screw locations in the edge of the door.