New floor and the Toilet

- The greatest concern would be humidity. Engineered flooring will still shrink and expand somewhat and it's very important to maintain humidity within a certain range. Manufacturers state that it should be kept within 30-50%. Due to the wide humidity level extremes RVs experience from summer to winter, that's not possible (in a house that's easy once it's built and occupied and heating and/or A/C is running). If you travel around the country, you could experience low humidity in one region and high in another. It's also very important to maintain the same humidity level on both sides of the engineered flooring and that's not possible either. The top finish layer can shrink and expand at a different rate than the substrate and some wood species could exacerbate damage from moisture changes. Failure to control the humidity level can result in serious and permanent damage.

You were doing pretty good until you got to the above paragraph. I've installed a lot of square feet of different engineered plank systems. I've installed in basements, in Hawaii (open patio door 1 mile from the beach), and in dozens of other homes where humidity is not controlled like you state. I have never seen a failure due to excessive humidity. As for controlling humidity underneath, that is part of the purpose of an underlayment or a plank that has an attached back. It is usually a caveat for basement installation.

If these engineered planks are installed in a high humidity area, the expanse of the floating floor will expand rather than the plank swelling and losing the veneer layer (in the case of wood veneer plank). The expansion is minute in each plank but many minutes can make up to a 1/4". My own experience is that, if the installation area is a typical residence on above grade level, the laminated planks will not expand even in the gap allowed for such. I have Pergo in part of my house that has not moved 1/32" in 20 years.