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Paper Side Insulation Direction

Posted by yoyoma (My Page) on
Tue, Oct 28, 08 at 13:29

Is it that big a deal whether the paper side of insulation faces inside or outside? My contractor needed to take the siding and felt paper off part of an exterior wall, and I told him since it's off, you might as well put in a higher R value insultaion. He said ok, but when I checked the next day, the worker put the insulation with paper side facing on the outside.

Should I have him redo it so the paper side faces inside, or can I just let it be? Thanks.


Follow-Up Postings:

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RE: Paper Side Insulation Direction

Depends on where you're located.

I'm in CT, a heating climate, so here vapor barriers go on the interior side of the wall.

If yours should be towards the interior, then have them correct it.

Mongo


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RE: Paper Side Insulation Direction

Spoke to the contractor, it should be on the inside, but since it's so small, and he said it doesn't really matter for such a small section, I decided to leave it as is. I am making him hang the felt paper over the new windows that were installed, because they put the felt paper before finishing flashing the flanges. Thanks.


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RE: Paper Side Insulation Direction

The paper side is the vapor barrier and it always goes towards the warmer side.

In cooling climates that it outwards, in heating climates it is inwards.

For most of the country with mixed heating and cooling it actually does not matter that much.

It will be wrong for half the year no matter what side it is on.


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RE: Paper Side Insulation Direction

"For most of the country with mixed heating and cooling it actually does not matter that much."

Does that hold true for floors and ceilings? Thanks.


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RE: Paper Side Insulation Direction

I realize this is getting academic, but I would think that there's a right answer to this question even in mixed heating and cooling climates. For example, in Ohio we might use AC to bring the house's temperature down by 15 degrees or so from a common summer high, but we use the heat to raise the indoor temperature by perhaps 50 degrees over a common winter low temperature. It seems that the danger of condensation would be greatest when the indoor/outdoor temperature differential is greatest.


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RE: Paper Side Insulation Direction

No matter which side faces in or out the paper side usually is actually a very poor vapor barrier anyway. Air/moisture will get around it pretty easy. If you really want a good vapor barrier cover the wall with heavy plastic and tape the seams.
While heat differential plays a large part, you also have to consider relative humidity, the side that is higher is where the moisture will be coming from trying to get to the dryer side.


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RE: Paper Side Insulation Direction

"While heat differential plays a large part, you also have to consider relative humidity, the side that is higher is where the moisture will be coming from trying to get to the dryer side."

Bingo!

If you have the Wood handbook form the Forest Products Lab it has (or at least my old copy does) a map showing the trade off location throughout the US.
Most of the country in the middle is in the middle were a vapor barrier is not really needed.
Try and get it past an AHJ though.


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