Upgrading crawl space insulation

[Olsteeen]

My 17-year-old crawl space is getting new insulation, 9" unfaced fiberglass batting and 2" foil-faced polyiso foam board facing the sealed dirt floor. Should the batting be faced toward the kitchen for thermal control or would that create an issue with double barriers?

 

[Maguire]

I'd stick with unfaced batting if you've got foil-faced foam below...double vapor barriers can trap moisture and facing it toward the kitchen could cause more issues than help with thermal control

 

[Olsteeen]

Yeah I'll keep the unfaced batting as is and avoid facing it toward the kitchen to prevent moisture issues. Thanks for your advice

 

[CircuitGeek]

My 17-year-old crawl space is getting new insulation, 9" unfaced fiberglass batting and 2" foil-faced polyiso foam board facing the sealed dirt floor. Should the batting be faced toward the kitchen for thermal control or would that create an issue with double barriers?

The golden rule for insulation is to put the vapor barrier on the 'warm side.' In a crawl space, that's the side facing your living area (the kitchen).
So, your unfaced batting should go up against the floor joists with no barrier. The polyiso foam board is your vapor barrier here, and it's on the 'cold side' (the ground). You're not creating a double barrier, so you're good to go

 

[Hermann Zapf]

The golden rule for insulation is to put the vapor barrier on the 'warm side.' In a crawl space, that's the side facing your living area (the kitchen).
So, your unfaced batting should go up against the floor joists with no barrier. The polyiso foam board is your vapor barrier here, and it's on the 'cold side' (the ground). You're not creating a double barrier, so you're good to go

Helping out my brother here. So just to be sure, if we're using unfaced batting and polyiso foam, we don't need any extra plastic sheeting, right? Also, does the foam board need to be sealed at the edges to work properly as a vapor barrier? Thanks1

 

[mamamew]

The foil on the polyiso acts as a vapor barrier and doubling up can sometimes lead to condensation issues, especially in older crawl spaces. Best bet is to keep the fiberglass unfaced as planned and let the polyiso do the heavy lifting on vapor control.

 

[Port Molyneux]

The foil on the polyiso acts as a vapor barrier and doubling up can sometimes lead to condensation issues, especially in older crawl spaces. Best bet is to keep the fiberglass unfaced as planned and let the polyiso do the heavy lifting on vapor control.

Thanks for the tip. I'm helping my cousin insulate his 1960s crawl space and we were debating whether to use faced batts or not. If the polyiso is doing the vapor control, do we still need a separate vapor barrier on the ground, or does that depend on the soil and moisture levels?