Man, you're gonna get lots of opinions on this one. Required? NO
I used Homasote as a base over my entire switching layout, then another level of homasote to raise the track as the actual roadbed. I also used cork on top of the base homasote in some areas just to change track elevations. My homasote roadbed is screwed into the base layer of homasote. I did not screw any of my track down though, I used brads instead. I didn't want any ugly screw heads showing. The brads are practically invisible.
These are cell phone pix but if you look hard enough, you can find the brad heads sunk down in the ties. I am very pleased with the sound level, even after the ballast went down.
