said by averagedude:
I went to Home Depot and had them cut down a 3/4"x4'x8' sheet of ply wood in to 24"x24" pieces. The 24"x24 boards match my rafter spacing. I nailed the boards down so they didn't move. It was not pretty, but it was safer.
No can do.
I have about 15" of insulation, the joists are only 2x4 (or 2x6, i forget).