I’m trying to install SPC LVP with 7.5 mm thicknesses after removing pre-existed laminate and carpet. I just noticed that there are metal joints on the subfloor which are about 3 feet long and 2 inches wide... any thought on what these are for? (One in a room and two in the hallway on second floor) Is it okay to remove it? Or is there any underlayment or any other item to avoid LVP on top of it not bending or making squeking sound?
Thanks!
That is a strap tie and is meant to distribute a load over a distance (usually across boards, joists, studs, etc.) I see it a lot in attics in Florida (ie hurricane straps) but not on floors. Placing one on a seam, such as the long strap, really doesn't distribute a load but it could be one of those "contractor" quick fixes (ie, I only have 2 straps when I need 4 and I'll just put it down quick and nobody will ever be the wiser ... until I'm long gone). The shorter strap actually looks like it may have been cut back as if someone noticed a bulge or tripped on it and decided to "remove it" without realizing it was a strap tie between two sheets of flooring.
Another thing I noticed is that the flooring appears to be OSB. Although OSB and even particle board get used on flooring, I personally don't like the results when either of these get wet. If it's not in a wet area (it appears to be an exterior entrance such as a mud room) and you don't live in a humid area of the country then you'll probably be fine BUT if you spill a lot of liquid on it or it gets damp over time and bulges and buckles then you'll know why (and have to replace that entire section of your floor). I've seen some people seal OSB and particle board flooring and that might be an option too as well as using marine plywood for wet areas.
As to the fix, I'd leave the straps in place and depending on the flooring you're going to use there are a variety of possible solutions. Carpeting, a nice thick padding should work okay. Laminate or hard wood flooring, notch out an area in the padding or wood itself just as deep as the strap is thick. Vinyl flooring, self leveling compound with a lauan plywood (1/8" thick plywood) to provide a clean smooth surface to attach vinyl or laminate). Tile, if it's level enough then your mortar/thin set will cover it as long as you're already level.
Here's where I found the straps in your picture (www.dhcsupplies.com/store/p/3804-ST9-Strap-Tie-1-1/4-X-9.html):
Those are typically used for seismic straps. I'm not too sure what purpose they would have being nailed down to the subfloor. Common application for them is to go diagonally across several studs on the outside of the sheathing, stiffening the framing, and preventing the house from over racking.
If it were me, I would pull a couple nails and see if it's nailed into anything solid. It looks like to me they run perpendicular to the joists instead of on top of them. You'll know by the amount of effort it takes to pull each nail. If the nails are sunk into the joists, then leave the straps. I still can't think of a reason for them there, but they're there for a reason. If the aren't sunk into the joists, or just a few are, then it's not doing any good regardless and yank 'em all out.
If you leave them, what you can try is pouring some self leveler about 12" wide (6" either side of the straps). That will allow you to put a vinyl flooring over the straps without them leaving an impression through the vinyl. The trick is making sure it's completely smooth, and you'll probably notice a raised spot each time you walk over there unless you can float it out further than 6" either side. Make sure you leave a minimum of an 1/8" skim coat over the nail heads, or all your work is for not.
Good luck!
