Faced or unfaced?

msaeger

I am going to use fiberglass bats to insulate the upper level of our 1 1/2 story.

When should I use faced vs unfaced bats? Do I just need paper faced in areas like the ceiling where I need something to hold it in?

Gary in WA

The faced batts are when you need/require a vapor retarder as per Code.



Find your Zone on or below the map: http://publicecodes.citation.com/ico...001_par001.htm



Find the insulation requirement by the Zone: http://publicecodes.citation.com/ico..._11_sec002.htm



Find the degree of vapor retarder/barrier required: http://publicecodes.citation.com/ico...001_par003.htm

Click on “next section“ below that (twice) to find different types and application of substitutes with different exterior siding/sheathing compositions.


Or just tell us where you live and I could give you the bottom line, but no one else would learn how to find it themselves…….

Gary

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msaeger

Thanks for the info I am in Minnesota zone 6A.

I already knew I needed a vapor barrier and this confirms it. The part I am having confusion about is weather or not the kraft facing counts as the vapor barrier.

So according to the site I can use class 1 or 2 which would says the kraft facing is good enough alone right? I would much rather use the kraft faced insulation over plastic, getting the plastic up is a pain.

The reason I am finding this confusing is because last time I did any insulating the inspector told me the paper facing was not enough because it didn't cover the faces of the studs. Sounds like a load to me but you have to do whatever they say if you want to pass. The insulation makers all say the purpose of the paper is the vapor barrier too so I think the inspector I got was just wrong.

I just bought some R21 with no facing but if I can avoid putting the plastic up I will return it and get some faced stuff.

msaeger

If I can just use kraft faced bats is an advantage to using unfaced and plastic?

Gary in WA

Studies have shown the plastic is over-kill for most of the U.S. This from Building Science Consortium; http://www.buildingscience.com/docum...nd-wall-design

The insulation manufacturer claims it is area weighed--- look for “Should the joints be taped?”, almost ½ way down the page; http://www.insulating-products.com/p...lation_FAQ.pdf

Notice the mention about face stapling? Can’t believe everything from them….Does make a difference; http://www.insulating-products.com/p...lation_FAQ.pdf

Pages 43-48 here; http://www.buildingscienceconsulting...Measure_Up.pdf



Show this to your inspector; http://www.buildingscience.com/docum...vapor-barriers

Use the ADA with drywall: http://www.buildingscience.com/docum...wall-approach/


Be sure to caulk the studs at the sheathing and the bottom plate to the sub-floor against air leakage= the biggest problem with fiberglass batts. Other than the convective loops in the low density junk and if it ever gets wet, or a hole in your inside air barrier. I put this together a while ago; The "biggest loser" in fiberglass insulation....


Gary

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msaeger

Wow thanks for the links!

I am now planning on just using kraft faced. That will be way easier to install I will just bring the stuff back I got and find someplace that has faced R21. The Menards close to here only has faced R19.

I noticed that the R19 was thicker than 6 inches and they tell you it's for a 6 inch wall so I thought that was weird but didn't think about the fact that compressing it would lower the R value. I just got R21 because I figured it wasn't too much more and it would insulate a little better.

msaeger

I think it's gonna be hard to find kraft faced R21 I think I will have to order it. I don't see any at Lowes or Home Depot online, I called Menards and they said they had to order it. I was going to just buy a couple bundles at a time until I got it all done but I guess I will just have to figure out how much I need and order it.

This stuff comes in R23 for a 5.5 inch bat. I don't think they make it faced though. http://www.roxul.com/residential/pro...tbatt%E2%84%A2

Windows on Wash

Great advice all around on this post.

Sealing up the air barrier is critical.

I have customers ask me why their upstairs is hot when they have 7" of blown in filterglass...go figure.

Gary in WA

Thank you for that, WW, and welcome to the forum! Page 21 of this good-all-around guide shows the caulking I mentioned some of while the cavities are open; http://www.engr.psu.edu/phrc/trainin...ngbarriers.pdf


Gary

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msaeger

Since I have the ears of some knowledgeable people here I have some more questions.

The knee wall is 2x4 framing but I was planning on putting thicker insulation in there and having it stick out the back past the studs into the empty area behind the knee wall. Is there any reason I shouldn't do this?

Windows on Wash

No harm in that. Just make sure you don't interfere with venting if that assembly is vented.

You will not be addressing the thermal bridging of the studs in this case and you would be better suited to stuff rigid foam between the rafters and attach it to the back side before you put more fiberglass up there but that will be a bit more costly and difficult.

msaeger

Putting rigid behind the knee wall sounds like a good idea but I don't think I want to do that. I just want to use the fiberglass bats if I can't

On the two end walls they are 2x6's so I am going to use R21. But for the rest I haven't decided yet. The knee walls are 2x4 the sloped part is 2x8 and the collar ties are 2x6.

I figure on the sloped part of the wall I will have to use R21 so I will have enough space for the baffles but for the knee wall and ceiling I could have the insulation stick out so I would like to use something else just because R21 is way more expensive than anything else.

I figure I could use R19 in the ceiling then put some un-faced stuff on top perpendicular to the rafters. Not sure what to get for the knee walls.

Windows on Wash

Staple up some radiant barrier on the other side of the kneewall framing and seal it to the backside of the stud.

Keeping the air from moving around in the fiberglass (even the HD stuff) will just help the R-Value and the radiant barrier will help take the sting out of the summer heating issues and keep that fiberglass working a bit easier than if it were exposed to the outside.

msaeger

Like this stuff? http://reflectixinc.cskern.com/image...all%200910.pdf

Is it worth doing extra stuff like this to the knee wall and not the rest of the areas? I suppose every little bit helps?

This stuff looks like they want you to use it for the vapor barrier on the hot side of the insulation except for the knee wall they have it on the cold side. So could I use unfaced fiberglass and staple reflectix in the stud cavities for the vapor barrier? Except on the knee wall they say to put it in the back so I don't know how that would work out.

heybales

No, you still need the vapor barrier on the warm side. The radiant barrier will just help keep some heat out of the resolution, and since you plan on having these exposed edges of insulation above the studs, will keep the air flow from making it less effective.

You should really just put in thick enough to reach the edge of the studs, and put some rigid foam up across the the whole length. Adds something to the studs, which don't have much R-value really.

In theory with your plan, during the evening summer hours where it's slightly cooler and more humid, if the upstairs room is nice and cool, the edges of those studs could get water condensation. Even if it's not dripping to some surface below, constant moisture is how you get mold growth.