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Author Topic: Question about insulating and vapor barrier  (Read 2266 times)
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DaveA (In Wisconsin)
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« on: February 24, 2007, 07:12:53 AM »

I hate insulating with a passion.  My question however relates to applying vapor barrier over insulation.............

A couple of the locals (myself included.....or should I say "Locos"?  Grin )
were debating insulating and where to apply vapor barrier.

I recall reading somewhere that vapor barrier should be placed over the WALL insulation and NOT in the ceiling.  The reason being that you want moisture to evaporate out through the o'head and NOT through the walls.

What is the opinion of those more experienced than I???

 
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Pat Copper
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« Reply #1 on: February 24, 2007, 07:31:28 AM »

vapor barrier. Paper side to heated area. As far as adding something else, such as poly, tis a BAD thing to do, at least in this climate. Tyvek on the outside of a new house, yes, poly on the inside tis a HUGE no-no at least in the mid-atlantic states and further south. and I wouldn't add poly if I lived on the north pole. A house HAS to "breath". stick ones head inside a plastic bag, and check out the breathing situation. Tis a rather suffocating experience. God that was bad.
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Gene Gauss
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« Reply #2 on: February 24, 2007, 07:53:31 AM »

In the northern climates, poly on the inside of the insulation is required.   Without the poly, "breathing" in the winter allows moisture to get into the insulation and freeze near the outside.  During a long cold winter, a lot of moisture can accumulate and when it thaws in the spring can lead to having a soggy mess.  It also doesn't insulate well when there's a layer of ice between the inner and outer sheathing.  I think Pat is correct in hot humid climates where the moisture would permeate from the outside and condense in the insulation if the inside is air-conditioned.  In that case, I'd probably consider using poly on the outside and let it breathe inward, but I've never lived in that kind of climate.  Gene Gauss
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Mike in Michigan
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« Reply #3 on: February 24, 2007, 08:33:43 AM »

When I  had my addition insulated with the semi-wet-blow-in-the-cavity insulation, the insulation contractor told me not to use visqueen on the walls. The ceiling is another story-he told me to install visqueen on the ceiling to keep out drafts from the ridge vent. The reason given, was since I was using knotty pine T&G on both the ceiling and walls, air could pass through the ridge vent on the roof and sneak past the T&G joints. The side walls did not require visqueen, since the exterior walls were sealed with Tyvek.
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Stu in Edmonton
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« Reply #4 on: February 24, 2007, 10:26:31 AM »

Simple explanation is poly or paper vapour barrier on the warm or heated side of the insulation on the walls and ceiling as well. I use 6 mil poly.
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Stu in Edmonton
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« Reply #5 on: February 24, 2007, 10:38:46 AM »

When I  had my addition insulated with the semi-wet-blow-in-the-cavity insulation, the insulation contractor told me not to use visqueen on the walls. The ceiling is another story-he told me to install visqueen on the ceiling to keep out drafts from the ridge vent. The reason given, was since I was using knotty pine T&G on both the ceiling and walls, air could pass through the ridge vent on the roof and sneak past the T&G joints. The side walls did not require visqueen, since the exterior walls were sealed with Tyvek.

Mike what is semi wet blow in? Is visqueen Poly?

If Visqueen is poly I would suggest that the ceiling application is necessary to stop vapour from migrating from the warm moist air of the house up into the cold attic space where it will freeze in the winter in Michigan. [When it thaws in the spring you got a mess.]  It will also stop drafts that find a crack thru the insulation. Of course the insulation in the ceiling will keep the area under it warm but it will also stop most drafts from roof vents if it is installed properly. That's why blown in is best for attic spaces. It falls into all the nooks and crannies.
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Bing in MN
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« Reply #6 on: February 24, 2007, 12:29:55 PM »

Yeah, I'm with Gene and Stu in Minnesota and Wisconsin climates you have got to have a vapor barrier (either the kraft paper or poly) to the warm side of all exterior walls and ceilings.  In addition to sealing up any protrusions like outlets.   New houses don't breath anymore but are tight and that's why a lot of new homes now have air exchangers.   You need to prevent the moisture from a warm area condensing on a cool surface and causing rot, mold, and soggy insulation.   Just take a look at the insulation on an outside wall without a vapor barrier sometime and there will be frost on it.  That's what you are trying to prevent.  Southern climates are different but in the north that guy is full of hooey.
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Mike in Michigan
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« Reply #7 on: February 24, 2007, 03:21:42 PM »

Stu, the semi-wet-blow-in is ground up cellulose mixed with just enough water to make the loose material stay in the cavity. They blow the insulation into the wall cavities, then they use a power tool that looks like the old fashioned reel type lawn mower to flush the insulation with the face of the stud. It is called NuWool in this neck of the woods.  When this stuff dries, the insulation is packed into the wall cavity, and there are no gaps.

And what I call visqueen, is actually 6ml poly.

The insulation in the ceiling of the room is dry, loose blown in cellulose.


« Last Edit: February 24, 2007, 03:27:41 PM by Mike in Michigan » Logged

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Jerry Purviance
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« Reply #8 on: February 25, 2007, 08:14:56 AM »

plastic ,visqeen . on the outside walls over the batt insulation .I don't put it on the ceiling. I do believe the moisture thing as well. I.e. no mold problem in any of my houses. Thats the way I've been doing it and will continue too.
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