If you build a house on post & pier foundation {say 30" off the ground},what do you put between the ground and the house and how would you insulate te pipes?
I would throw R30 under the floor if you have enough space. Then I would attach 2 inch rigid foam insulating beneath that to serve as extra moisture protection and add about an r factor of 8 or so.
Of course as Steve said it depends on where you are. Here in Vermont its impossible to insulate too much.
I seem to recall that the vapor barrier should be facing the living space. Otherwise you trap moisture in the insulation and floor joists. On new construction this is pretty easy to do by putting the kraft faced insulation between the joists (paper side up) before you lay down the floor sheathing.
Otherwise, I believe they say to use the unfaced insulation when insulating existing floors. To make your life easier, I've seen encapsulated fiberglass insulation. It has a perforated wrap that makes it easier to handle and retain between the joists.
On floor joist insulation I think the "kraft" face is down. Moist air is lighter than dry air and rises. A vapor barrier on the ground and good crawl space vents are a must also.
I was taught that the moisture barrier should face the heated surface, so in a basement or crawl space that would leave the fiberglas exposed. I think its usually done the other way because its easier and looks a little nicer.
Andy, I think the " <font color="blue">should face the heated surface </font color> applies to interior walls and ceilings. For unheated crawl spaces no vapor barrier should be used on the insulation. A vapor barrier should be used over the ground. If you do use insulation with a kraft face in this application it should be down. That said, go here for the straight skinney on your application Owen Corning
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