Attaching Advantech subflooring to the underside of an exposed floor assembly – GreenBuildingAdvisor

My question is what fasteners should I use when attaching subflooring on the bottom side of a raised floor? Specs below.

I know that Huber recommends #8 or #9 screws, but given that the sheets will be inverted and not really bearing on anything underneath I am concerned about the possibilities of eventual tear-out of sheets through the screw heads.

So, what about using 4″ Simpson SDWS screws? They have a nice, wide low-profile head that I can probably Liquid Flash over. I know they’re not Huber-approved, but neither is an inverted panel.

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I’m in zone 6 and the floor assembly is on piers, 6″ off grade. Underneath is 12 mil poly and 4″ of trap rock.

From the bottom up:

Advantech X-Factor subflooring (inverted and attached to the rims and joists through the rigid panels with something?)

1 1/2″ rigid (EPS or XPS?)

 – Liquid Nails Projects & Foamboard High Strength Paste Adhesive to glue the XPS to the joists and rims on the top side, and to the faces of the Advantech on the bottom side

13 3/4″ Unfaced batts (compressed to 11 1/4″ for R-42)

Advantech X-Factor subflooring

 -Tytan Subfloor Pro High Yield Adhesive to glue the subfloor to the joists and rims, and .131 nails

Some kind of wood flooring