Always follow the flooring manufacturer’s instructions for preparing and leveling the sub-floor. Make sure the sub-floor is structurally sound, level and clean. Check for protruding nails and/or defects in the sub-floor. If installing underlay over concrete, the concrete must be dry with moisture emission rates that do not exceed 3 lbs, per 1000 square feet, per 24 hours, as measured by the Anhydrous Calcium Chloride Test.
Install one roll of the 3-in-1, or 2-in-1, flooring underlayment parallel to the wall in the opposite direction as you plan to install the flooring planks. Cut the foam underlayment with a utility knife leaving at least 2″ going up the wall. Install the planks making sure that you are still able to see the edges of the underlay so that you can properly align the next roll.
Install the next roll of underlayment, butting the foam seams together. Make sure not to overlap the foam, and join seams with seaming tape. (If applicable, remove the adhesive liner and adhere to the overlap film)
Continue to install the planks and your preferred grade of Silent Surface foam underlayment, as in step 3. The final 2″ of the foam will be covered by finish molding, or trim if no molding will be installed.