Subfloor beef up and 1/4” polystyrene siding underlayment

[JLDrumStudio]

8F0C9626-1A6D-4F9D-BC41-88D9DAD5A2E3.jpeg

I have a unique situation as I begin my subfloor beef up. I have open web joist, so I only have 1 1/2 to fit my two 5/8 drywall with green glue and backer rod. Yes I know it’s not the best way but I have to bend my staples over and cut/bend a few nails. Like I said I only have an 1 1/2 to work with here because of the open web joist. My question is I want to use this 1/4” polystyrene siding underlayment to smooth out the subfloor and also make it easier for my cleats since that and two layers of drywall equal my 1 1/2 I’m working with. The 1/4” polystyrene has needle holes about every inch or so moister can escape when used for siding. Are these tiny needle holes going to effect me in any way. 3rd leaf? I just don’t want to bury this stuff and find out later it bites me in the ass lol Thanks.

[JLDrumStudio]

That’s a generic pic of the open web joist. I wish mine was that clean and smooth.

[Gregwor]

I have to bend my staples over and cut/bend a few nails.

Why don't you cut off the end of the stapes and grind off the ends of the nails?

Like I said I only have an 1 1/2 to work with here because of the open web joist.

This is no different than I-joist's a lot of us have to work with. The solution is to make L shaped cleats.

I want to use this 1/4” polystyrene siding underlayment to smooth out the subfloor and also make it easier for my cleats since that and two layers of drywall equal my 1 1/2 I’m working with.

Don't. I'm afraid it will make a third leaf situation. Plus, if you deal with the staples and nails as I've suggested, the green glue will be more than good enough with any discrepancies on the bottom side of your subfloor.

Greg

[JLDrumStudio]

Thanks Greg for the info. I will cut the staples as well. Are you suggesting I use green glue on my first layer of 5/8 drywall to the subfloor and then again in between the two layers of drywall sheets?

[Gregwor]

Are you suggesting I use green glue on my first layer of 5/8 drywall to the subfloor and then again in between the two layers of drywall sheets?

If you can afford it and want the little extra the second layer offers, sure. But I think GG has documented that extra layers don't add crazy benefits acoustically. If I were you, I would just apply their recommended amount to the first layer and then not put it on the second layer. The stuff is expensive.

Greg