Retrofitting from knob and tube. One location has a rafter directly above where the light should go (and currently is). The ceiling is 3/4 in beadboard. Can I use a 4 inch pan box cut in to the beadboard, and then a junction box above and next to the rafter for the wiring? Should the bottom of the pan box be flush to the bottom of beadboard? 
Electrical – Rafter above location for light, exterior light box choice
electricalretrofitwiring
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Best Answer
I'd use a saddle box instead
Instead of trying to cobble together something out of two different boxes, raising issues of access to the upper box, I would use a saddle box that fits around the rafter instead, as shown below (photo for exposition only). This provides adequate space for splicing while allowing easy access to all the wiring here just by dropping the fixture.