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Old 06-17-2011, 07:56 AM   #1
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Which way to face the vapor barrier?


I know it's usually "towards the warm side" but hear me out for a second.

I have a 1930 cape cod with an addition off the back. The house has a full basement, the addition has a crawlspace.

The "floor" of the crawlspace is dirt and is covered by a giant plastic sheet (I call it a sheet because as much as I want to call it a vapor barrier - who knows what it is.

The concrete walls are not insulated (Just like the "regular" basement)

In between the floor joists is tucked fiberglass insulation with the vapor barrier facing down.

I can't figure this one out.... I mean technically I could make an argument for both sides being "warm". The basement has 1 vent down there and year round it never gets cold. The room on top of the crawlspace has several vents and obviously never gets cold either (although it's always colder than the rest of the house).

First of all I can't figure out why the insulation is there - and second of all I can't figure out why the vapor barrier is facing down. If one side really has to be "warm" - wouldn't it be the side upstairs that is heated w/ several vents?

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Old 06-17-2011, 09:07 AM   #2
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Which way to face the vapor barrier?


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Originally Posted by CoconutPete View Post
I know it's usually "towards the warm side" but hear me out for a second.

I have a 1930 cape cod with an addition off the back. The house has a full basement, the addition has a crawlspace.

The "floor" of the crawlspace is dirt and is covered by a giant plastic sheet (I call it a sheet because as much as I want to call it a vapor barrier - who knows what it is.

The concrete walls are not insulated (Just like the "regular" basement)

In between the floor joists is tucked fiberglass insulation with the vapor barrier facing down.

I can't figure this one out.... I mean technically I could make an argument for both sides being "warm". The basement has 1 vent down there and year round it never gets cold. The room on top of the crawlspace has several vents and obviously never gets cold either (although it's always colder than the rest of the house).

First of all I can't figure out why the insulation is there - and second of all I can't figure out why the vapor barrier is facing down. If one side really has to be "warm" - wouldn't it be the side upstairs that is heated w/ several vents?
In the basement the paper side down so as to staple to the studs to keep it in their. Now in the attic the paper side down the same to staple it to the studs. Dry wall goes over the studs.

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Old 06-17-2011, 10:03 AM   #3
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Which way to face the vapor barrier?


Insulation vapor barrier always goes toward the heated side, which means that it goes up toward the floor in crawlspaces and unheated basements. It is held up in place by stiff wires (called "tiger claws") that stretch between the floor joists, if properly installed, which yours isn't.
It is stapled to wall studs and ceiling joists in heated spaces.
An attic vapor barrier goes down toward the ceiling underneath insulation batts, but it doesn't matter which way it faces if it is stapled to the roof joists in an unheated attic. It really serves no purpose in that instance.
Good Luck!
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Old 06-17-2011, 10:28 AM   #4
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Which way to face the vapor barrier?


CocountPete,

Sometimes we give the people who built and insulated our homes a little too much credit.

You figured out the right way to insulate your floor right away. They didn't know what they were doing.

P.S. love the screen name
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Old 06-17-2011, 11:22 AM   #5
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Which way to face the vapor barrier?


OK, so I'm not going crazy or missing anything - thank you!

The next problem is that approximately 20% of the insulation batts are starting to fall down due to:
A: Not being attached properly
B: It's been there for 50 years
C: A combination of A and B

Should I just yank it out? I've only been in the crawlspace once, but does the dirt floor make it a lot colder than my regular concrete basement?

As long as the vapor barrier doesn't do anything negative then I guess I could just tuck it back up there and use the claws to hold it in place.

This won't really be an issue until the winter, but I don't want to be stuck with the problem in November.

Thanks - If you ever have 2 hours to kill - Club Dread is one of my favorite movies (That's where CoconutPete is from).

Last edited by CoconutPete; 06-17-2011 at 11:24 AM.
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Old 06-19-2011, 09:38 PM   #6
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Which way to face the vapor barrier?


In a heating climate, the crawl space insulation vapor retarder goes up. In a cooling climate, it goes down. Same with the walls-inside w.heating, outside w. cooling.

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Old 06-20-2011, 01:40 PM   #7
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Which way to face the vapor barrier?


Where is the house? Are we all meant to assume the location is in a ''heating zone"?

There are plenty of areas where it is neither heating nor cooling, so since we don't know where the house is located, we are giving generalisations...

In other words, it was a matter of opinion when that insulation was put in.
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Old 06-22-2011, 02:30 PM   #8
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Which way to face the vapor barrier?


It all depends on where you are?
If you live where its cold most of the time, the vapor barrier goes on the inside, if you live where its hot, it goes on the outside.

Vapor barriers (a plastic sheet) very often cause more troubles than they solve.

In the north, its always warmer indoors, this means high water vapor/humidity levels indoors and cold dry outside, the idea of a vapor barrier is to stop the water vapor migrating into the walls, ceilings and floors.......But, they are very often poorly installed! (they need to be airtight at least, and water vapor proof (very difficult to do) as the water vapor molecules can get through the tiniest hole) they are much smaller than air molecules.

Then water vapor gets inside the walls etc, condenses onto the cold wood, makes it wet, if it cannot dry to the outside then mold and wood rot can start.
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Old 06-27-2011, 08:59 AM   #9
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Which way to face the vapor barrier?


If people say the vapor retarder goes toward the warm side, then why in the south do people always put the kraft faced paper down in the attic? I'm trying to insulate a master bath and by the approach of putting the kraft paper toward the outside (hot) then i should also put the kraft paper facing up in the attic above. But it seems i've always seen the kraft paper facing down in the attics.

Does anyone have familiarity with Johns Manville comfort therm without a vapor retarder? http://www.jmhomeowner.com/products/...t=ComfortTherm Wondering if this would be good to use (or better than faced or unfaced batts) in exterior wall applications with tar paper used on the outside of the sheathing.
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Old 06-27-2011, 02:25 PM   #10
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Which way to face the vapor barrier?


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If people say the vapor retarder goes toward the warm side, then why in the south do people always put the kraft faced paper down in the attic? I'm trying to insulate a master bath and by the approach of putting the kraft paper toward the outside (hot) then i should also put the kraft paper facing up in the attic above. But it seems i've always seen the kraft paper facing down in the attics.

Does anyone have familiarity with Johns Manville comfort therm without a vapor retarder? http://www.jmhomeowner.com/products/...t=ComfortTherm Wondering if this would be good to use (or better than faced or unfaced batts) in exterior wall applications with tar paper used on the outside of the sheathing.
==================================
The logic of this is that you put the vapor barrier on the side of the wall where the vapor is!
In areas that are cold in winter, the vapor created by people is on the inside of the house and the space outside the home is usually colder and drier (but not always)
In places where it is hot and humid outside and cold and dry indoors the barrier is placed on the outside of the wall.
Having written all that.....please be aware that a vapor barrier by itself is not a good idea!
Water vapor has very tiny molecules, very, very much smaller than air molecules it is almost impossible to stop it moving through or round most barriers.
To make it work...it needs to be backed up with at least three inch thick polystyrene.
Three inch polystyrene is thick enough to avoid creating a dew point on one side of the barrier....dew points= the temperature where water vapor turns into water.
You do not want water inside your wall.
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Old 06-27-2011, 02:49 PM   #11
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Which way to face the vapor barrier?


Thanks Perry, but that's my question. If you are supposed to put the paper on the outside of the wall in hot humid climates, why do I always see the paper facing down in attics?
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Old 06-27-2011, 02:53 PM   #12
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Which way to face the vapor barrier?


Because some people think those are stapling flanges.
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Old 06-27-2011, 07:43 PM   #13
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Which way to face the vapor barrier?


That smilie always makes me laugh. I'm not sure I follow. It's not stapled anywhere, the paper is laying on the floor in the attic with the insulation being what you see. But if the paper is supposed to be facing toward the hotter side (attic apposed to room below) the insulation should be facing down with the paper on the top.
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Old 06-28-2011, 07:41 AM   #14
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Which way to face the vapor barrier?


It is sad to say that not very many people seem to understand how humidity/water vapor/condensation works.

When you do understand, you know that fiberglass and cellulose are rubbish insulation and that they cannot work.

Water vapor is produced in the home by cooking, washing, breathing, sweating, by house plants, fish tanks, flowers, animals all these put water vapor in the air. Our breath is 100% saturated.

As long as the air remains warm, it can hold anything between one and five teaspoons of water per cubic metre of air.

When air drops below 40F it is almost dry.

When you turn the heating off or down the air gets cold and the water vapor looks for somewhere to condense, usually on a cold window, or a glass of cold beer.

Failing those it is inside your walls or roof.

The way to stop it entering the walls and ceiling/passing through to the cold outside, is to use a vapor barrier.

But, the vapor barrier has to be water vapor proof, that means better than airtight, and batts are anything but water vapor proof. It needs to cover the walls and ceiling turning the room into a water vapor proof box, almost impossible to do and, when you do manage, then because it can be room temperature on one side and humid, and cold on the other, the water vapor in the room will condense on the room side and turn in to water, running down behind your drywall. Unless you back it up with three inch thick polystyrene.

Water vapor passes through and round batts as if they are not there, so it doesn't matter which way they are fitted, because they are a waste of space.

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