Foil faced fiberglass insulation…..what to replace it with?
merlvern
| Posted in General Discussion on
I’m renovating my master bath, and for a number of reasons had to remove both the drywall ceiling and the foil faced insulation (to the attic) in the ceiling. I wanted to take this opportunity to better insulate the ceiling but find that Foil faced insulation doesn’t seem to be used for this anymore. My understanding was that it was not only a vapor retarder, but a “thermal” reflector. What should i replace it with? Kraft faced? Vapor barrier with unfaced?
I should mention……i have to do this from underneath, so blown in is not an option…..i was going to “push the batts” up between the joists/rafters and staple to ceiling side of structure
Sorry if this seems like a silly question…..any help would be appreciated.
Replies
Nothing silly about it. Experts debate this all the time. For smaller projects, mineral wool is my go-to. I'm actually the guy in the lead photo in this article: https://www.finehomebuilding.com/project-guides/insulation/mineral-wool-makes-a-comeback
Mineral wool is stiffer than FG, and easier to cut precisely to fit around obstacles. Buy an insulation knife. A steak knife or bread knife also works well, but only if you're a bachelor or wish to be one.
Sure is an honor to hear from someone I’ve read for years!
Thanks for the input.....I gather 2 things from what you’re saying...
Foil isn’t necessary, and you’d default to something that gives a tight air barrier
Appreciate the help
Thanks for the good words! Funny thing about all the FHB staff and contributors - We're all just regular people who lucked into glossy print. Almost none of us live in finished houses...
The mineral wool doesn't give you the air barrier. That's going to be your drywall in this case. If you want to really do it right, run a bead of acoustical sealant (Not sure where you are, but Kamco sells it in New England. Any good drywall supply house should have it.) between the bottom plate and the drywall. You can also gasket the electrical boxes. A couple of coats of paint is all the vapor retarder needed until you get into Zone 4.
One thing to consider is laying an additional layer of unfaced insulation at right angles to the joists, as far as you can reach while you have it open, then placing another layer between the joists.
You can use unfaced for both, and then end with a vapor barrier. This will work better than any faced insulation product, since it will only have edges to deal with at the perimeter of the part you are replacing. Reflective layers work best with an air gap, so i would not worry about looking for a reflective solution for this application.
Uncle, I like that idea about crisscrossing the joists
I wonder about the vapor barrier....much of what I read in zone 4 tells me I should worry more about air transfer and that something like 4mil plastic can be more problematic than helpful. Do you have any other thoughts on that?
Really appreciate it
Yes. I should have put a heating zone caveat on the vapor barrier idea.
https://insulationinstitute.org/im-a-building-or-facility-professional/commercial/installation-guidance/managing-moisture-in-commercial-construction/vapor-retarders/