1/8" over 6' flatness check

I always try to follow instructions (right mom?), but I ask in return an explanation of why it is as it is. This is one such example: the flatness check manufacturers ask us to do before installing their products. I know we put down a 6' straightedge and check for anything above 1/8" and fill it in or shave it down, but why 1/8" over 6'?

Does this mean that the board will "bend/give" up to 1/8" so that it will lay flat on the subfloor? This guess might be enough for you to tell that I need some help with this!

 

Everything in the world has tolerances that are acceptable, lets just assume that the manufactures have done their due diligence and found what that tolerance is so that when complete we are satisfied.

 

While this is posted in the flooring forum, you have not told us what you plan on installing. Most flooring installs recommend a 1/4" in 10' which would be similar to your calculations in 6'. Give us some more detail so we can advise.

 

Sorry! I was asking in general as that particular tolerance seems to be pretty standard across many manufacturers and others. I will be putting down a 5 1/8" x 3/4" engineered oak floor that has a 4 mm wear layer. This is over a 5/8" plywood subfloor. The core is a filleted quarter-sawn softwood, not ply. The manufacturer recommends the above tolerance in their instructions.

I'll follow that but I just wanted to know why. One answer seems to suggest that the manufacturers know why but I want to know as well. Is it because the boards will nail down easily and flush if there is a 1/8" or less gap compared to a larger gap? Or is it something else?

czizzi, can you pass along a link to where in the flooring forum the info is listed? I searched the forum but came up empty.

 

Regardless of the spec you should fill in low areas to eliminate the gap.

1/8 gap can be resolved with several layers of roofing felt, goal should be flat!

 

Low spots cause undo strain on the flooring. Sounds like you are nailing down and not floating so you are in better shape. Your boards are wide so keep that in mind. Also, sounds like you are not installing "true" engineered flooring as it has a soft core.

Does the manufacturer recommend nailing form the groove side as opposed to the tongue side? Those that recommend that are not as high a quality as traditional full "plywood" style engneered flooring which is substantially more stable and stronger overall.

 

It is nail down floor and yes, through the tongue side. This is a new product from Preverco (Canadian manufacturer) called Max19. Your comment re "true" engineered might need to be amended to "old" engineered. It has a quarter sawn filleted core instead of the plywood and time will tell whether this is the future or just a fad in engineered flooring. I have my warranty card filled out just in case!!