I'm having contractor install Hickory engineered hardwood floors over plywood underlayment he said it can be glued or nailed. The sales person says it should be nailed. I'm also hearing it should be glued. As you guessed confusion has set in. Not sure of the level of the floor. I'm completely in the dark on this one and need some help from someone who has experience in installation. I live in N. CA. Thanks in advance for your help.

Depending on width 5" and wider should have a bead of glue. Personally I'd never full spread a floor over a wood sub-floor or wood underlayment, repairs are hard to do.

Thanks for the information I've since decided to go with the nail installation. The cost of glueing is not cost effective.