[h4pjc]

I am in climate zone 3. North of the warm-humid line. I am insulating an attic. Should I use faced or unfaced insulation? Unfaced is less than faced, so I'd like to go that way, if possible.

 

[Bud9051]

Unfaced should be fine and is preferred.

Bud

 

[carpdad]

Thinking about it over the years, if I had to do thing over, I would use faced. Face down touching the drywall below then 2nd layer facing up. Face paper is supposed to be a vapor barrier but with proper air seal and acrylic paint used now, how much moisture from below? With proper air management above, how much moisture from above and outside? My reasoning is that fiberglass insulation will be more efficient with less air moving through it with kraftpaper left on. At most, few cuts would let the moisture out?

 

[Bud9051]

Here;s some reading :

https://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers

Bud

 

[carpdad]

My problem with articles like it is that it talks a lot about the walls which is a different install from attic insulation installs. It's all about how vapor may travel but attic is different from air sealing the walls. I know that if I left the face paper on top it can trap the moisture in the air and condense into water, but air flowing over the insulation seems to be a problem too. It's like we're giving up on attic air problem because drying out is more important?

I still have to add some insulation in my attic. How about if I added unfaced insulation and loosely cover the insulation with something like tyvek? Would tyvek allow drying out? I'm not looking for the absolutes, btw.:smile: I also plan to run the attic vent fan which increases the air movement.

 

[h4pjc]

Thanks for the reply. If I go unfaced, and I want to install it before the sheetrock, what is the easiest want to keep it suspended?

 

[Bud9051]

The easiest way to install unfaced insulation is from the attic after the drywall is up.
I didn't catch that this is new construction where the facing does provide the edges to make for a neat installation.
@carpdad, attics are different from walls and the attic numbers have already taken advantage of that extra space above. If you meet or exceed the minimum code levels where you are any reduction from air infiltration has already been considered. As for adding a condensation layer on top, be it the facing or house wrap I see more risk than reward, but I would have to do a lot of searching to find the science papers to support that. As with most guidance the advice suggests the best practices without saying all others are bad. But when bad happens it can be ugly. More reading.
https://www.buildingscience.com/documents/insights/bsi-073-macbeth-does-vapor-barriers

Bud

 

[Nealtw]

My problem with articles like it is that it talks a lot about the walls which is a different install from attic insulation installs. It's all about how vapor may travel but attic is different from air sealing the walls. I know that if I left the face paper on top it can trap the moisture in the air and condense into water, but air flowing over the insulation seems to be a problem too. It's like we're giving up on attic air problem because drying out is more important?

I still have to add some insulation in my attic. How about if I added unfaced insulation and loosely cover the insulation with something like tyvek? Would tyvek allow drying out? I'm not looking for the absolutes, btw.:smile: I also plan to run the attic vent fan which increases the air movement.

If you have sealed the ceiling from the attic and have enough insulation up there You can consider it unconditioned space and storing some tyvac up there should not hurt anything but i doubt there is a problem that tyvac will fix.

 

[carpdad]

"reduced value calculated in", paraphrased, is a new info. That was easy enough.:smile: Again, thanks.