Replace the floorboards and then spray more insulation on top of it.
How to insulate 2x6 roof rafters.
If you have a solid floor covering the roof rafters use the claw end of a hammer to pull the floor up in several locations and blow the insulation under the boards.
How to insulate 2x4 rafters.
There are some unfinished crawl space areas in the corners on the upper floor.
R 19 is made for 6 inch framing and if you installed the vent trays properly there should have been enough air movement in the cavities to prevent condensation on the back of your roof sheathing without nailing extensions to the rafters.
I have a 1925 bungalow in michigan climate zone 5.
For example if the space beneath the rafters is going to be used for a living area then you will need to insulate the roof rafters.
For rolled insulation place it between roof rafters.
If your attic rafters are 2 by 6 inch framing members i assume you used an r 19 batt insulation.
Although there are many different circumstances that may call for insulating roof rafters the means to determine the necessity for insulating rafters remains the same.
Look for water stains on the roof sheathing or damp or moldy spots on attic joists and existing insulation as a clue to where leaks might be.
It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow.
Box out light fixtures.
If you choose to use the 2x6 roof joists you ll only be able to fill the joist space up about 4 5.
They are directly below the roof sheathing and are were insulated with fiberglass batts stapled between the 2x4 rafters.