Two questions-should or should'nt I put an underlayment down. Home Depot said it was'nt necessary when I bought the flooring. But I have read things that say I should for sound etc. The instructions say "you can." It is above ground level on sub floor. Second question is we want to change flooring direction between two rooms in an open floor plan that has no doors. What should we put down where the two meet to allow expansion joint. Would it have to be a raised transition strip there?