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Old 01-06-2011, 07:30 AM   #1
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Vapor Barrier Confusion! ???


Ok the holidays are over and I can FINALLY get started on the new house. I have taken all the sheetrock down, HOPEFULLY this weekend will be replacing all the switches, outlets and boxes. Next weekend I want to start rerocking, am probably going with FG insulation, what is the true deal with a vapor barrier. Should I be using one or No? Living in Philadelphia, EXTREME temp swings with the season. Can be 98+ in the summer with high humidity and 24- in the winter. In this order? wiring/insulation/vapor barrier/sheetrock??? Is there a specific vapor barrier to use? 6mil plastic?

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Old 01-06-2011, 08:19 AM   #2
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Vapor Barrier Confusion! ???


If you use Kraft Faced Fiberglass batts, no need for another Vapor Barrier. Follow the instructions in installing the Fiberglass, and you will have no problems

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Old 01-06-2011, 11:50 AM   #3
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Vapor Barrier Confusion! ???


And remember... vapor barrier toward the conditioned (warm in winter, cooled in summer) side.
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Old 01-06-2011, 12:23 PM   #4
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Vapor Barrier Confusion! ???


I'd suggest checking with your local building dept.6 mil poly might be the required vapour barrier in your area.If so you will want to place poly of some sort behind your new electrical boxes. If faced insulation is allowed and used that is the only vapour barrier required.Do not use plastic in addition.( use one vapour barrier only)
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Old 01-06-2011, 12:55 PM   #5
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Vapor Barrier Confusion! ???


I am assuming that by faced insulation you are talking about the paperbacked as opposed to 100% pink fiberglass?! (Which happens to be what WAS up there) But was OLD dry rotted and crumbled in my hands! haha

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Old 01-06-2011, 01:17 PM   #6
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Vapor Barrier Confusion! ???


It can be Pink, white, yellow, orange. The Kraft facing has tar applied to it to help allow for use as a Vapor Barrier. If you are going to use 6 mil. use unfaced, Roxwool, recycled Bluejeans. Use of a double vapor barrier will do nothing.
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Old 01-06-2011, 01:57 PM   #7
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Quote:
Originally Posted by gregzoll View Post
It can be Pink, white, yellow, orange. The Kraft facing has tar applied to it to help allow for use as a Vapor Barrier. If you are going to use 6 mil. use unfaced, Roxwool, recycled Bluejeans. Use of a double vapor barrier will do nothing.
Greg, thank you for your reply, I am referring to the standard pink fg insulation. (not sure how the backing is applied?) But that is what I am using is the pink fg with brown paper on the back. Just wanted to make sure I didn't need the plastic vapor barrier if that is what I was using.

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Old 01-06-2011, 02:32 PM   #8
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It all depend on the amount of your heating days; “Polyethylene, a plastic sheet material, can be used as a vapor diffusion retarder for above-grade walls and ceilings (only) in very cold climates (in locations with 8,000 Heating Degree Days or higher).” From; http://www.energysavers.gov/your_hom.../mytopic=11810

Your location has only 5000- H.D.D. so a facing retarder would be enough, not the plastic; http://www.climate-zone.com/climate/.../philadelphia/



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

Find your location from the City/State list below the map; http://publicecodes.citation.com/ico...001_par001.htm


Zone 4A wall insulation requirements; R-13 required; http://publicecodes.citation.com/ico..._11_sec002.htm



Fiberglass batts are not created equal, don’t use “the biggest loser”; http://www.diychatroom.com/f98/how-b...ulation-90438/

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Old 01-06-2011, 02:36 PM   #9
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Quote:
Originally Posted by Evil Scotsman View Post
Greg, thank you for your reply, I am referring to the standard pink fg insulation. (not sure how the backing is applied?) But that is what I am using is the pink fg with brown paper on the back. Just wanted to make sure I didn't need the plastic vapor barrier if that is what I was using.

Thanks again
ES, the paper backed insulation does not do a good job as a vapor barrier, regardless of what the manufacturer might claim. Every single join on every stud will allow air to pass through. The idea is to prevent air infiltration in either direction, as this is the major contributor to heat loss.

If you can find it, use Roxul and 6 mil poly for your v/b. The Roxul is 10% higher R-value for the same thickness. I believe the 4" Roxul is R-14 and the 6" is R-22. And it is far easier to use than fiberglass. Once you try it you'll never touch f/g again.

You can get plastic condoms to fit around your electrical boxes, which keeps the v/b intact.
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Old 01-06-2011, 02:39 PM   #10
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Vapor Barrier Confusion! ???


Since you are using insulation with a backing paper do NOT use poly.
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Old 01-06-2011, 02:59 PM   #11
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Quote:
Originally Posted by daveb1 View Post
Since you are using insulation with a backing paper do NOT use poly.
Perhaps you misunderstood me.

I did not suggest he use poly with a paper backed product.

Respectfully, paper backed f/g is a very old technology. It simply is nowhere near as good as a 6 mil poly v/b. It damages too easily and does a lousy job of stopping air movement.

If you can locate a copy, read the January 2011 issue of Fine Homebuilding magazine, which has a series of excellent articles covering many phases of energy saving and insulating.

Many years ago, a gentleman by the name of Edward Mazria wrote the definitive book on the subject. It is an excellent read.

Up here in Canada, where we take these things very seriously, there was a major push by the University of Saskatchewan to design a well insulated house aimed at using drastically less energy. They worked with a select few builders and achieved spectacular results.

Back in the day of UFFI insulation, Simon Fraser University (Vancouver) ran a highly intense 40 hour course on every conceivable aspect of insulating. Even back then, the paper v/b wasn't worth installing.

I hope this may have cleared up any confusion I might have caused, for which I apologize.
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Old 01-06-2011, 07:55 PM   #12
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Vapor Barrier Confusion! ???


Roxul is a good product, but poly vapor battier is not for his location. Department of Energy sites quoted and 2009 IRC are the Codes he needs to follow for his location. His HDD are not enough to warrant poly which will give him trouble in the summer weather.

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Old 01-06-2011, 07:59 PM   #13
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Quote:
Originally Posted by GBR in WA View Post
Roxul is a good product, but poly vapor battier is not for his location. Department of Energy sites quoted and 2009 IRC are the Codes he needs to follow for his location. His HDD are not enough to warrant poly which will give him trouble in the summer weather.

Gary
Could you explain why poly wouldn't be good there Gary?

I have never heard of that before.

Thanks.

Gary: I just realized that you posted all your information while I was typing my much earlier reply. Sorry I didn't read backwards, which I should have done.
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Last edited by cocobolo; 01-06-2011 at 08:37 PM. Reason: Missed an earlier post.
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Old 01-06-2011, 08:32 PM   #14
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Vapor Barrier Confusion! ???


Quote:
Originally Posted by cocobolo View Post
Perhaps you misunderstood me.

I did not suggest he use poly with a paper backed product.

Respectfully, paper backed f/g is a very old technology. It simply is nowhere near as good as a 6 mil poly v/b. It damages too easily and does a lousy job of stopping air movement.

If you can locate a copy, read the January 2011 issue of Fine Homebuilding magazine, which has a series of excellent articles covering many phases of energy saving and insulating.

Many years ago, a gentleman by the name of Edward Mazria wrote the definitive book on the subject. It is an excellent read.

Up here in Canada, where we take these things very seriously, there was a major push by the University of Saskatchewan to design a well insulated house aimed at using drastically less energy. They worked with a select few builders and achieved spectacular results.

Back in the day of UFFI insulation, Simon Fraser University (Vancouver) ran a highly intense 40 hour course on every conceivable aspect of insulating. Even back then, the paper v/b wasn't worth installing.

I hope this may have cleared up any confusion I might have caused, for which I apologize.
I was just trying to reinforce to ES to not use a double vapour barrier.I agree with you that properly applied poly is a far superior method than the paper backing but apparently is not recommended or approved for his climate/area.
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Old 01-06-2011, 08:49 PM   #15
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Vapor Barrier Confusion! ???


Quote:
Originally Posted by daveb1 View Post
I was just trying to reinforce to ES to not use a double vapour barrier.I agree with you that properly applied poly is a far superior method than the paper backing but apparently is not recommended or approved for his climate/area.
Dave, yes, I missed Gary's post completely when I posted earlier. He posted while I was apparently typing. I have just a few minutes ago edited my earlier post to reflect that.

For the life of me I cannot imagine why anyone would not want to use the best vapour barrier available. Some of the codes south of the border really baffle me completely...it makes no sense.

However, I am hoping that Gary - who is a whiz at all this stuff - can enlighten me. I'm always extremely willing to learn.

But...and there's often a but...those old codes may be changing. Please - if you have the opportunity to read the January issue of FHB (above) - by all means do so.

FWIW a large part of the problem has been artificially low energy costs in the US, and there has been little or no need to improve any of the insulation/vb standards.

Don't misunderstand me, I am in no way suggesting that everyone who has quoted the code is wrong. No doubt that is precisely what the code says. Sometimes things need to change and can be done better. I believe this just may be one of those times.

If it was my house, poly it would be. I'm paying the energy bill, not someone who may have written the code 30 years ago.

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