Nate R
Member
1 1/2 story 900 SF house in Milwaukee built in the early 20s. No basement.
I have wall cavities that are built w/ studs between 3 7/8" and 4" thick. (The house was built w/ reused wood from another structure.)
The rafters on this house are also 2X4s (Really nearly 2" wide and nearly 4" in depth) and there is a cathedral ceiling in some of the house on the upper floor.
In the stud cavities, I've been planning on using R13 Fiberglass batts. But that leaves me some extra space. I do want to insulate this house pretty well, as we plan on being here for a while, and paying the house off in about 7 more years. Anyway, I bought some 1/2" Polyiso rigid foam board w/ foil facing. But this brings up the vapor barrier issue.
Here's a stackup of the materials from drywall to the outside.
My first thought, w/o any consideration of vapor barriers/retarders, was :
Drywall;
R13 Fiberglass Batt Kraft Faced Insulation;
1/2" Foil Faced Polyisocyanurate Foam Sheet; (R3)
Original 1X6 sheathing boards;
3/8 OSB for racking resistance; (The sheathing boards are perpindicular to the studs, not diagonal, and there's no let-in diagonal 1X4 or anything. And there's been some racking over the years because of it. I don't want it to go any further.)
1/2" or 3/4" foam; (Styrene or Polyiso?)
Tyvek;
Vinyl Siding.
Obivously, the 1/2" polyiso sheet is a problem w/ water vapor, since putting it tightly against the inside of the sheathing, and then having kraft faced batts makes for a double vapor barrier. The foam I use on the outside could become an issue as well depending on what type I use.
So, what are your thoughts on how I SHOULD do the stackup here to be proper? And Why?
I've been reading that Extruded polystyrene is not a vapor barrier, but a retarder, and is OK to use on the outside of the sheathing if the joints are NOT taped.
But I believe foil faced polyiso is a vapor barrier. Should I use unfaced batts, and put the polyiso just behind the drywall instead of against the sheathing?
Or should I find some 1/2" extruded polystyrene and use that inside the sheathing instead?
Or use the polyiso as the current stackup shows, and just leave small gaps around some of the edges between studs and between pieces so moisture can travel in and out? I mean, this works for kraft faced insulation (cutting slits in it) right? So any reason I can't use the iso i already bought as shown above as long as I leave some gaps (1/8" or so) around them"
Thanks for any input! I need to figure it out soon, as my wife wants to reinsulate a wall cavity we have open. Right now, the exterior side isn't as shown above, but will be eventually. We have the batts and the polyiso to do the cavity, but I didn't want to do it until I was confident in the manner in which we do it.
I have wall cavities that are built w/ studs between 3 7/8" and 4" thick. (The house was built w/ reused wood from another structure.)
The rafters on this house are also 2X4s (Really nearly 2" wide and nearly 4" in depth) and there is a cathedral ceiling in some of the house on the upper floor.
In the stud cavities, I've been planning on using R13 Fiberglass batts. But that leaves me some extra space. I do want to insulate this house pretty well, as we plan on being here for a while, and paying the house off in about 7 more years. Anyway, I bought some 1/2" Polyiso rigid foam board w/ foil facing. But this brings up the vapor barrier issue.
Here's a stackup of the materials from drywall to the outside.
My first thought, w/o any consideration of vapor barriers/retarders, was :
Drywall;
R13 Fiberglass Batt Kraft Faced Insulation;
1/2" Foil Faced Polyisocyanurate Foam Sheet; (R3)
Original 1X6 sheathing boards;
3/8 OSB for racking resistance; (The sheathing boards are perpindicular to the studs, not diagonal, and there's no let-in diagonal 1X4 or anything. And there's been some racking over the years because of it. I don't want it to go any further.)
1/2" or 3/4" foam; (Styrene or Polyiso?)
Tyvek;
Vinyl Siding.
Obivously, the 1/2" polyiso sheet is a problem w/ water vapor, since putting it tightly against the inside of the sheathing, and then having kraft faced batts makes for a double vapor barrier. The foam I use on the outside could become an issue as well depending on what type I use.
So, what are your thoughts on how I SHOULD do the stackup here to be proper? And Why?
I've been reading that Extruded polystyrene is not a vapor barrier, but a retarder, and is OK to use on the outside of the sheathing if the joints are NOT taped.
But I believe foil faced polyiso is a vapor barrier. Should I use unfaced batts, and put the polyiso just behind the drywall instead of against the sheathing?
Or should I find some 1/2" extruded polystyrene and use that inside the sheathing instead?
Or use the polyiso as the current stackup shows, and just leave small gaps around some of the edges between studs and between pieces so moisture can travel in and out? I mean, this works for kraft faced insulation (cutting slits in it) right? So any reason I can't use the iso i already bought as shown above as long as I leave some gaps (1/8" or so) around them"
Thanks for any input! I need to figure it out soon, as my wife wants to reinsulate a wall cavity we have open. Right now, the exterior side isn't as shown above, but will be eventually. We have the batts and the polyiso to do the cavity, but I didn't want to do it until I was confident in the manner in which we do it.