Laminate floors are “floating” floors and thus aren’t fastened to the subfloor. That actually makes the condition of the subfloor more critical to the success of your installation.
Left unleveled, a subfloor that isn’t smooth and flat could cause your laminate flooring planks to squeak or separate.
When you check how level your subfloor is, you’re looking for a peak or valley more than 1/8th of an inch within 40 inches of grade. These subtle differences can sometimes be hard to spot just by looking.
How to determine whether the subfloor is level, and what to do if it isn’t
Take any laminate plank and lay it on its end, dragging it across the subfloor. As you find a low spot, mark it with a green marker; find a high spot, mark it with a red marker.
Once you’ve determined the low and the high spots, you’ll want to even out those differences. We recommend using a Portland-based leveler or leveling compound to fill in and grind down the peaks. Allow the leveler to dry overnight before beginning installation. As with any product, always read the complete leveling compound instructions first.
The goal while thinking about leveling the subfloor is to have a clean, smooth and level surface upon which to install laminate flooring. Remember, laminate flooring with attached underlayment padding can accept a deviance of 1/8th of an inch over 40 inches. Any low spots of 3/16th of an inch or greater must be filled in with leveling compound.