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Kraft paper required on fiberglass batts?

Joe.B

Joe.B

Registered User
Joined
Dec 4, 2020
Messages
942
Location
Myrtletown Ca
Got one that has me stumped. I am relatively new on this side of the counter but sometimes I think that's an advantage because I don't simply believe something because that's "the way it is."

Had a builder yesterday say that he's waiting on his insulation because we are one of the last areas that "require kraft paper on fiberglass insulation batts." He didn't know if that was a "California thing" or a "climate zone thing." (We are climate zone 1) He said that's what the company he uses told him, and there's a shortage right now. So I scoured the code books and I can't find anything close to this. Any ideas on where this is coming from? Is it a manufactures requirement? UL listing requirement? Best practice?

And for discussion sake, what kind of insulation installs do you usually see in your area? Moisture barriers? Vapor barriers? I've seen a major shift away from fiberglass to rockwool and/or spray foam. Do you see requirements for a 3rd party QII inspection? (Quality Insulation Installation)

Thanks.
 
Kraft paper is a class II vapor retarder, and in ICC land is only required in climate zones marine 4, and 5,6,7,8 prescriptively (some instances allow a reduction to a class III but I rarely see that). I am in zone 5. Most production builders here use a third party, above code program and do use a QII inspection, though I think our inspectors still do an insulation inspection. Not in the field much but I would say still quite a bit of fiberglass going in. Customs are more likely to use foam than productions.
 
Sifu said:
Kraft paper is a class II vapor retarder, and in ICC land is only required in climate zones marine 4, and 5,6,7,8 prescriptively (some instances allow a reduction to a class III but I rarely see that). I am in zone 5. Most production builders here use a third party, above code program and do use a QII inspection, though I think our inspectors still do an insulation inspection. Not in the field much but I would say still quite a bit of fiberglass going in. Customs are more likely to use foam than productions.
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I went down the vapor barrier rabbit hole a while back and determined that is wasn't required in our climate zone. I thought it may be where the kraft paper would be beneficial, thanks for bringing that up. It's a good reminder.
 
The kraft paper makes it easier to staple so it stays in place. I prefer cellulose for walls because it restricts air movement better. I'd like to try Johns-Manville Comfort-Therm plastic-wrapped fiberglass for ceiling insulation in my new house, thinking that the plastic wrap might keep attic air out of the insulation and make it more likely to achieve the full R-value.
 
Paul Sweet said:
The kraft paper makes it easier to staple so it stays in place. I prefer cellulose for walls because it restricts air movement better. I'd like to try Johns-Manville Comfort-Therm plastic-wrapped fiberglass for ceiling insulation in my new house, thinking that the plastic wrap might keep attic air out of the insulation and make it more likely to achieve the full R-value.
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I agree that the paper makes the batts easier to install. What I find interesting in many of the houses that I've seen built here the insulation installers (when installing fiberglass batts) will use the batts with paper on the exterior walls and paperless for the interior walls. I've often asked why they don't use the same batts everywhere because they're easier to install. The answer is usually "it's cheaper" and sometimes "it's only for noise reduction." Apparently the paper-less batts are better at reducing noise? That's their belief anyways.
 
I have only seen paper faced batts on old (and I mean old) remodels. Typically see either R22 batt, blown in, or an R20 with outboard foam. Only consideration we have is the vapour permeance of the foam due to vapour barrier being installed on the inside of the building envelope.

Once in a while we see some sprayfoam, but there are issues with sealing between joints in the lumber for the continuity of the plane of air tightness.
 
tmurray said:
Careful now, he's in climatic zone 1. Our good habits for installing a vapour barrier on the inside in heating climates are actually bad habits in the cooling climates. Gotta love physics.
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Interesting that you say that, I had conversations with some builders asking why local insulation installers always staple to the inside of the stud bay instead of overlapped on the narrow edge of the stud. My research determined that the drywallers would complain about the paper binding up the screws they used to install the drywall. Now as I'm researching this I wonder if by overlapping the kraft paper they would be creating a vapor barrier when you really don't want one. Very interesting, thank you.
 
Joe.B said:
Interesting that you say that, I had conversations with some builders asking why local insulation installers always staple to the inside of the stud bay instead of overlapped on the narrow edge of the stud. My research determined that the drywallers would complain about the paper binding up the screws they used to install the drywall. Now as I'm researching this I wonder if by overlapping the kraft paper they would be creating a vapor barrier when you really don't want one. Very interesting, thank you.
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No, for kraft paper to meet the permeability of a required to be considered a vapour barrier, it would need to be so thick that use would become impractical. As Sifu mentioned, it is a vapour retarder, which is more like a vapour throttle than an actual barrier.
 
When you're filling out the energy compliance forms up here in Marine 4, you have two vapor barrier options

Kraft-faced insulation, which must be installed so the paper flaps overlap each other on the 1-1/2" stud face, not to the 5-1/2" face...to form a continuous 'barrier' of kraft paper on the interior surface.

The other option, instead of kraft paper facing is to use a PVA primer or sprayed-on paint vapor barrier. Back in the day...circa mid 90's we always opted for the painted vapor barrier and I still remember doing the rounds with the inspectors during our PVA inspections where they would take this little card out and place it against the freshly painted surface to measure the thickness of the PVA being applied to make sure it met code specs.

Personally I always spec kraft paper as a standard in plans, allowing the contractor to change it to the PVA if they want later.
 
Stapling the Kraft paper to the sides of the stud or rafter will create voids and would allow cold spots. There is a very good video on the net on how to install insulation showing a badly installed batt and a properly installed batt. (I think it was done by Owens-Corning)

I have only heard from my previous drywaller that polyethylene can cause drywall nail pops and that he hated the blown-in cellulose insulation because his installers complained about the material getting in their face. The other complaint was he couldn't use glue with the poly.

The US government took polyethylene out of their requirements for ceilings several years ago, the fella that wrote the regulation said that ceilings would trap moisture and some ceilings had come down, he was promoting cellulose insulation at the time when I attended his seminar at our local electric coop.

We're in Zone 4 and I see Kraft in the outside walls and unfaced batt insulation in the interior walls on occasion for sound. We see blown cellulose in the attics here about 90% of the time.

We do not see poly on an exterior wall unless they are using an unfaced batts, but no poly in the bathroom walls, typically see WR drywall.
 
Joe.B said:
I went down the vapor barrier rabbit hole a while back and determined that is wasn't required in our climate zone. I thought it may be where the kraft paper would be beneficial, thanks for bringing that up. It's a good reminder.
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That is a very deep rabbit hole. Glad you made it back out.

I don't know much about climate zone 1. But here is climate zone 5A we find that Class I and II vapor barriers are great if you are trying to grow mold in your walls (that is sarcasm for those of you who do not recognize sarcasm). Moisture gets into the wall cavity from the outside. Don't ask me why contractors fail to seal the exterior from moisture intrusion. Maybe contractors are doing there best and there is some other moisture contributor. But we have mold in our hospital walls - especially where the walls have vinyl wallcovering. Walls that have no vapor barrier are allowed to breath and dry out. No vapor barrier = no mold. We have found that kraft-faced insulation may be listed as Class III but it performs like a Class II. Therefor we do not allow kraft-faced insulation.
 
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BayPointArchitect said:
That is a very deep rabbit hole. Glad you made it back out.

I don't know much about climate zone 1. But here is climate zone 5A we find that Class I and II vapor barriers are great if you are trying to grow mold in your walls (that is sarcasm for those of you who do not recognize sarcasm). Moisture gets into the wall cavity from the outside. Don't ask me why contractors fail to seal the exterior from moisture intrusion. Maybe contractors are doing there best and there is some other moisture contributor. But we have mold in our hospital walls - especially where the walls have vinyl wallcovering. Walls that have no vapor barrier are allowed to breath and dry out. No vapor barrier = no mold. We have found that kraft-faced insulation may be listed as Class III but it performs like a Class II. Therefor we do not allow kraft-faced insulation.
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If where you live is warm or wet, vapour barriers on the inside of walls is a bad deal. That vinyl wall covering, yup, it's a vapour barrier. If you are using a vapour barrier (not a retarder, but an actual barrier) in those climates, put it on the outside. Let the building envelope dry to the inside.
 
Code says manufactures installation instructions are over the code. Looks like the manufactures installation instructions say to attach it to the studs ether way or use those tension wires.
 
Rick18071 said:
Code says manufactures installation instructions are over the code.
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Provided that said instructions do not violate code, right? To be code compliant products need to be installed per manufacture's directions and not violate any code provisions. That's my understanding anyways. A good example I see is the location of sediment traps for gas lines supplying appliances. California code is very specific about the location of the sediment trap, after the shut-off valve, before the flex connector, and as close to the appliance as possible. Most installation instructions I've seen show the shut-off, then flex connector, sediment trap, appliance. This would be a case where following the manufactures installation instructions would technically violate code. Granted it's not a big deal as long as the shut-off valve is first. I've seen plenty where the sediment trap is before the shut-off valve and that should always be corrected, IMO.
 
Don't know about CA code but this is IMC
304.2 Conflicts. Where conflicts between this code and the
conditions of listing or the manufacturer’s installation
instructions occur, the provisions of this code shall apply.
Exception: Where a code provision is less restrictive than
the conditions of the listing of the equipment or appliance
or the manufacturer’s installation instructions, the conditions
of the listing and the manufacturer’s installation
instructions shall apply.
 
Rick18071 said:
Don't know about CA code but this is IMC
304.2 Conflicts. Where conflicts between this code and the
conditions of listing or the manufacturer’s installation
instructions occur, the provisions of this code shall apply.
Exception: Where a code provision is less restrictive than
the conditions of the listing of the equipment or appliance
or the manufacturer’s installation instructions, the conditions
of the listing and the manufacturer’s installation
instructions shall apply.
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The most restrictive applies, that matches what I was thinking. The CA Plumbing and Mechanical Codes are based off of the Uniform Codes produced by IAPMO and generally are more restrictive than the international codes, except when it comes to pressure testing gas lines, there's it's less restrictive.

2019 CA Plumbing Code 102.1 Conflicts Between Codes. Where the requirements within jurisdiction of this plumbing code conflict with the requirements of the mechanical code, this code shall prevail. In instances where this code, applicable standards, or the manufacture's installation instructions conflict, the more stringent provisions shall prevail. Where there is a conflict between a general requirement and a specific requirement, the specific requirement shall prevail.

Similar enough. On a plumbing note, our code does not allow AAV's (air admittance valves) which IPC allows. Ever run into issues with those? For gas pressure tests our code requires a minimum of 10psi for 15 minutes, I hear the IFGC is far more complicated than that. What's your experience there?
 
JB,
We allow the AAV's and 90% are used due to poor planning or laziness. I write it for being installed incorrectly in most island counters, they typically install it to low below the sink.

Gas pressure test 20psi for 15 minutes
 
I usually suggest using AAV's in on older homes (more than 50 years) that are being renovated where they installed a s trap where their was one before and most of the time they get it right when I tell them not to use the cheep black ones Home Depot sells. It's a lot easier to add an AAV where there was no vent before in an existing house.
All most all gas piping I see is for propane which I see a lot of code violations but is against the law for me to inspect. Usually missing nail plates, supports and bonding.
 
In the past 50 years I have not seen a requirement for kraft paper on insulation in any national consensus code nor is it a good practice in my opinion. If there is a requirement for a vapor retarder on the warm side of the insulation its best to use 4 mil polyethylene but it doesn't appear to be required in zone 1. The supplier appears to be pulling the contractor's leg.
 
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