Hello all,

I am remodeling a 1950’s home that is built on a pier and beam system with 4×6 girders spaced 48″ oc and 2×8 t&g subfloor.  The 2×8’s are old, cracked, and shrunken so I’m putting down 3/4″ t&g ply on top of it as a new subfloor, which is also my subfloor in the addition, which is built on 2×6 joists.  The finish floor will be 3/4″ oak.

I’m going for an energy efficient home and will be sealing my attic space, using a membrane WRB on the walls, and exterior insulation.  I’ll be making it as airtight as I can and will be using an ERV.  I would have sealed my crawlspace as well but my wife isn’t as excited about this sort of thing as I am…  So here are my questions:

1. What should I do about air sealing my floor?  Tape the plywood seams?  Caulk the seams?
2. Do I need a vapor barrier?
3. Would it make sense to lay down a membrane of some sort on top of the plywood to handle air and vapor?

I also need to add minimum R-19 insulation in my ventilated crawl space between these girders.  Any recommendations?

I’m thinking about installing 2’x4′ or 4’x8′ sheets of mineral wool or rigid foam between the girders and screwing them into the 2x subfloor.  And this insulation should probably be decided along with the air and/or vapor barrier.

Thank you for any input you may have!
-Aaron