To maintain any warranty in the flooring, Yes. It is really going to sound loud, without any cushion.

Rosin Paper is useless . you need a underlayment pad for the imperfections in the floor . Quick Step makes a good one , and their top of the line has a good moisture barrier on it . Tape the seems with a foil tape not Duct tape . QuickÂStep® Unisound Combi Floor

@Tyler G - all cork floating floors have an integrated underlayment. The thickness will vary between price points but they all have them. The issue is the wonky subfloor. That's your biggest issue. To reduce the effects of this problem, you would want to use the 1/4" cork to get rid of *SOME of the issue. You will still have some movement in the floor (a snick of bounce when you walk over a low spot) but not as bad as when laying a floor straight over top. To get the most benefit out of your situation, the cork floating floor + 1/4" underlay will offer the "most for the least". That is to say the most comfort/acoustics/price advantage/longevity for the least amount of work/disturbance to your rented home. You can't do the work on the subfloor that is needed (it really is needed if you want the floor to live 20+ years). So you have to do as much as possible to reduce the effects of the wonky subfloor. And that means investing in a decent, rigid underlayment like cork. Even though the cork sheets are flexible, the cork itself is rather rigid. It doesn't "squish" down very much (it is actually rated for porcelain tile installation). That means it will even out the wonky subfloor - just enough to get you a cork floor that should live 15 years or so. Please remember to use transition strips at all doorways. This is another way to ensure your floor will get you more than a decade worth of life.

Underlayment comes in two categories: rigid (like plywood, OSB or luaun) and soft (like foam, cork or felted material). Which one are you talking about? And how was the old engineered floor installed? Floating, glue, nail, staple, cleats?