# Taping seams on kraft faced insulation



## AlphaPilot

Have you before? I'm thinking I will put in the extra effort. Seems to differ from each manufacturer. I won't have a poly film so I am relying on the kraft/paper face to be my vapor barrier on my R-38 12" insulation - zone 5. I'm guessing the edges that I staple to my truss bottom chord are fine and that the seams don't need taped - but I will have a seam every 48" because the insulation is only 48" long batts. That's a lot of points vapor could move, right? :vs_worry:


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## Windows on Wash

Are you putting up sheet rock?


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## AlphaPilot

Windows on Wash said:


> Are you putting up sheet rock?


Yes! I know you don't see it taped...normally, if ever. But you also normally see attic insulation rolled up in longer lengths than 48" - this results in 6 to 7 seams per truss cavity. Multiplied by 30 to 40 truss cavities results in a lot of seams. If a vapor retarder is needed on the ceiling (pretty sure it's advised) then I wonder how much of it would be compromised by that many seams. If it were unfaced insulation and I installed a vapor retarder poly, I imagine those seams would need taped. :vs_worry:


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## Windows on Wash

If the sheet rock is taped and gets a couple of coats of paint, the taping of the seam on the kraft paper is more meaningless at that point. 

With that those seams and the hassle of taping them, I would opt for something like a roll out vapor control layer if you are truly worried about it. Google Mem-Brain. 

For the record, I don't think you need to worry about it.


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## Bud9051

I agree with Windows. Unless local code is requiring a vapor barrier, for which the Kraft usually doesn't qualify, your painted drywall and good attic ventilation should be sufficient. More importantly would be air sealing around any ceiling light boxes and air tight (AT IC rated) recessed fixtures. Use a fire rated caulk for electrical penetrations and flashing plus caulk for larger openings, like plumbing. Air leaks into the attic move much more moisture than diffusion through the drywall.

Bud


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## Windows on Wash

Good points Bud. 

The caulking and sealing is critical before sheetrock goes up.


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## AlphaPilot

Valid points indeed. I have 10 recessed LED Trim lights that are IC rated, not sure about AC ? When you mention the flashing and fire rated caulk for larger openings, what is the flashing? I so far have only used a couple cans of 'fireblock great stuff' it's pink in color and has ASSTM ratings but I am not sure other than that. I haven't seen fire rated caulk but am sure I just never was looking for it. What do you suggest needs sealed prior to sheetrock on the ceiling? I imagine most sealing is down during and after the sheetrock is put up, such as running beads of caulk along the plates before sheetrock is installed to seal the gap. Also running caulking along the perimeter of fixtures where drywall butts up against them.


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## Bud9051

Metal flashing like roof flashing.
That would be AT not AC and it stands for Air Tight.

@ Alpha "I imagine most sealing is down during and after the sheetrock is put up, such as running beads of caulk along the plates before sheetrock is installed to seal the gap."
We wish, but drywall is usually attached directly to studs. The only thing in between would be the Kraft edges or plastic vapor barrier if either were used. A few of the newer homes may have sealed the drywall. But, in addition to drywall at the top plate are all of the electrical and plumbing penetrations. Some major air bypasses occur under tubs, sinks, over kitchen cabinets, around heat ducts, beside chimneys, and of course recessed lights and electrical boxes. Once air leaks into any wall cavity it can follow a meandering path to the attic or outside. 

I'll attach a link from Efficiency Vermont that does a good job of identifying many leakage issues.
http://www.efficiencyvermont.com/stella/filelib/TBC_Guide_062507.pdf

Just Google the fire rated caulk, several to choose from.

Bud


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## Gary in WA

The joints in paper face need not be sealed in your VAPOR barrier as it is area weighed unlike an AIR barrier- where any hole is detrimental- big difference; Download and *page 5*; http://buildingscience.com/document...retarders/view?topic=/doctypes/researchreport

Code only requires a vapor barrier when attic space above is unvented; http://publicecodes.cyberregs.com/icod/irc/2006f2/icod_irc_2006f2_3_par171.htm

With your faced insulation, code allows; As an alternative, the net free cross-ventilation area may be reduced to 1/300 when a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling." From; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_8_sec006.htm 

Asphalt paper-facedis avapor retarder- with no classes; *"*
*VAPOR RETARDER.* A vapor resistant material, membrane or covering such as foil, plastic sheeting, or insulation facing having a permeance rating of 1 perm (5.7 × 10-11 kg/Pa × s × m2) or less, when tested in accordance with the dessicant method using Procedure A of ASTM E 96. Vapor retarders limit the amount of moisture vapor that passes through a material or wall assembly."A Class 2, as the 'Download" said. Since you are concerned about quality; add some housewrap (or 3" cellulose) over the top of your low-density 1/2# per cubic ft. fiberglass http://www.diychatroom.com/f98/biggest-loser-fiberglass-insulation-90438/
whichcould have heat-robbingconvective loops if temp differences are 50*f or more in attic from room below. R-30 FG gives R-18 at 20*F... due to convective losses.


ADA the drywall ceiling/walls; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/


Gary


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## AlphaPilot

Bud9051 - I am installing the drywall, so I plan on taking the effort to use caulking on the top and bottom plates and against each partition wall before installing drywall. Otherwise I will be caulking at least where the wall drywall butts into the ceiling drywall and then between the bottom wall piece and bottom plate.

Gary - Thank you. I unfortunately do not know the density. more than likely it's nothing fancy or high density. Perhaps in the future I could blow in cellulose. House wrap would be a nightmare to install in my roof system. Plus it would need to be 24" pieces running along each truss cavity. I do have foam baffles in every truss. I also have a raised heel roof to get more insulation at the kneewalls.


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## Gary in WA

From "biggest loser link; 
"My local box store carries; 
*R-13 HD* at *1.0*# density 
R-19 at 0.55# density 
*R-21 HD* at *0.90*# density 
R-30 at 0.57# density 
R-38 at 0.53# density"

Your R-38 is a low density- with inherent convective loops if a vented attic- baffles or not; robbing you of heat 24/7.

Gary


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## AlphaPilot

Gary in WA said:


> From "biggest loser link;
> "My local box store carries;
> *R-13 HD* at *1.0*# density
> R-19 at 0.55# density
> *R-21 HD* at *0.90*# density
> R-30 at 0.57# density
> R-38 at 0.53# density"
> 
> Your R-38 is a low density- with inherent convective loops if a vented attic- baffles or not; robbing you of heat 24/7.
> 
> Gary


How would house wrap be applied effectively (besides very...very...time consuming)? Or shall I just assume blow in is the best idea..?


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## Windows on Wash

If you are talking about a large attic space, just blow it with loose fill.


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## Bud9051

A common practice up here is to blow in a couple of inches of cellulose as a cap to add insulation and reduce air infiltration.

As for fiberglass in an attic being vulnerable to air infiltration, I have always assumed that was one of the reasons why ceiling the r-value requirements are much greater than walls.

Bud


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