I did a 48 hr moisture test and the concrete is dry (40 years old, but partly below ground level.) I have 5.5 mm engineered vinyl planks. I also have some leftover 3 mm and 4 mm felt underlayment with a vapor barrier attached. I read I should use a vapor barrier over concrete, but the underlayment's attached vapor barrier is on the TOP side of the felt underlayment. So do I first lay down a plastic vapor barrier of 6 mil, then the felt underlayment with the vapor barrier on TOP and then the planks? Or can I turn the underlayment upside down and have the attached plastic vapor barrier on the bottom, with the felt on top, with the planks on top of that?
