# Vapor Barriers



## Bubbas Boys (Apr 11, 2013)

Ok so I know there is a lot of confusion about them. We are building our home and are ready for the wall coverings. We are using old barn wood and used corrugated metal. I havr seen sone debate about the usefulness of it and want some opinions. I know the air and vapor can pass through easier with the materials we are using but in my mind it shouldn't get trapped either with the open cracks and holes in our material. Should I put up plastic on walls or not? Thanks.


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## homstdr74 (Jul 4, 2011)

Plastic wrap is used in almost every new construction project done commercially. But there was a thread about that on this HT site not too long ago, and the general consensus about its use was mostly negative. Some had said that it deteriorated rapidly under the siding, others that it did more harm than good. 

Years ago, when it was an inexpensive recyclable product, I sheathed the framework of the home I built with aluminum printer's plates. top, bottom, sides, all of it. Now that's not a "vapor barrier" per se, but we've had good luck with it in this climate. I also used 4x8 sheets of insulation board on top of that, covered by old-fashioned 30# tarpaper, covered with oak siding and heavy metal roofing. 

The comments on that thread about the modern tarpaper were also negative, though. What if you put the insulation board with foil on one side all the way around, and made it tight? I wonder if that wouldn't satisfy the "vapor barrier" principle? Yes, I know that the plastic also has small "weep holes" in it, but we've never had that sort of condensation problem with the system I put up.


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## NorthwoodsMike (Jun 10, 2013)

Bubbas Boys said:


> Ok so I know there is a lot of confusion about them. We are building our home and are ready for the wall coverings. We are using old barn wood and used corrugated metal. I havr seen sone debate about the usefulness of it and want some opinions. I know the air and vapor can pass through easier with the materials we are using but in my mind it shouldn't get trapped either with the open cracks and holes in our material. Should I put up plastic on walls or not? Thanks.


Are you referring to interior walls? If so, what kind of insulation will you be installing? In cold climates, a vapor barrier is pretty important, as humidity from inside the home will cause condensation within your insulation and on the inner side of the exterior sheathing.


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## wharton (Oct 9, 2011)

homstdr74 said:


> Plastic wrap is used in almost every new construction project done commercially. But there was a thread about that on this HT site not too long ago, and the general consensus about its use was mostly negative. Some had said that it deteriorated rapidly under the siding, others that it did more harm than good.
> 
> Years ago, when it was an inexpensive recyclable product, I sheathed the framework of the home I built with aluminum printer's plates. top, bottom, sides, all of it. Now that's not a "vapor barrier" per se, but we've had good luck with it in this climate. I also used 4x8 sheets of insulation board on top of that, covered by old-fashioned 30# tarpaper, covered with oak siding and heavy metal roofing.
> 
> The comments on that thread about the modern tarpaper were also negative, though. What if you put the insulation board with foil on one side all the way around, and made it tight? I wonder if that wouldn't satisfy the "vapor barrier" principle? Yes, I know that the plastic also has small "weep holes" in it, but we've never had that sort of condensation problem with the system I put up.


 You are confusing an interior vapor barrier with an exterior house wrap, and or exterior insulation. Vapor barriers are there to prevent the migration of water vapor into the wall, from the INTERIOR of the structure. They can be plastic sheeting, kraft paper faced insulation, or other materials. It can vary in effectiveness from a total waste of time and material, to a completely air tight surface that absolutely prevents any air or moisture from penetrating the barrier. As for it being the right thing to do? I'll pass on that answer. Lots of very serious proponents and detractors in that debate.


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## lonelytree (Feb 28, 2008)

I won't build anything without a totally sealed vapor barrier. Tape the seams and any holes you poke in it. I liked how Tyvek tape adhered to it. I even taped around outlets etc.


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## homstdr74 (Jul 4, 2011)

wharton said:


> You are confusing an interior vapor barrier with an exterior house wrap, and or exterior insulation. Vapor barriers are there to prevent the migration of water vapor into the wall, from the INTERIOR of the structure. They can be plastic sheeting, kraft paper faced insulation, or other materials. It can vary in effectiveness from a total waste of time and material, to a completely air tight surface that absolutely prevents any air or moisture from penetrating the barrier. As for it being the right thing to do? I'll pass on that answer. Lots of very serious proponents and detractors in that debate.


Regardless, I've never had a problem with the way I've done it. I know that's not the way you're supposed to do it, but I did and I also put some 30# tarpaper on the inside of the framing, then sheathed that with ply/OSB covered by sheetrock. I put up the first part of the structure over 36 years ago, and have had an opportunity to look at the framing since. Still looks as new as the day I drove the first nails into it.


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## lonelytree (Feb 28, 2008)

homstdr74 said:


> Regardless, I've never had a problem with the way I've done it. I know that's not the way you're supposed to do it, but I did and I also put some 30# tarpaper on the inside of the framing, then sheathed that with ply/OSB covered by sheetrock. I put up the first part of the structure over 36 years ago, and have had an opportunity to look at the framing since. Still looks as new as the day I drove the first nails into it.


Why would you add the expense and labor of ply/OSB on an interior wall that is going to be covered with sheetrock?


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## homstdr74 (Jul 4, 2011)

lonelytree said:


> Why would you add the expense and labor of ply/OSB on an interior wall that is going to be covered with sheetrock?


Strength. Those 4x8 sheets of wood have a tremendous shear strength and are impervious to the same damaging blows that would puncture sheetrock.


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## Oldfashiondad (Jan 26, 2014)

The thing about using an actual sheet of plastic for your vapor barrier is that it is not breathable. The Tyvek brand house wrap is a breathable sheeting that not only inhibits moisture from transferring from the exterior of the home to the inside if the wall, it allows any moisture inside the walls to evaporate. Something plastic cannot do. With regular plastic, you may fight condensation on windows and doors because the home cannot "breathe". Creating what is referred to as a "sick home."


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## NorthwoodsMike (Jun 10, 2013)

Oldfashiondad said:


> The thing about using an actual sheet of plastic for your vapor barrier is that it is not breathable. The Tyvek brand house wrap is a breathable sheeting that not only inhibits moisture from transferring from the exterior of the home to the inside if the wall, it allows any moisture inside the walls to evaporate. Something plastic cannot do. With regular plastic, you may fight condensation on windows and doors because the home cannot "breathe". Creating what is referred to as a "sick home."


I agree. I would NEVER use plastic on the outside. Inside of insulation, yes, but never outside.


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## fishhead (Jul 19, 2006)

If I had the focus to read this I think it would answer a lot of questions. 

http://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers


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## fullmetal (Nov 2, 2013)

i very firmly believe in sealing all exterior surfaces (walls, roof, windows, etc) to a hermetic level, and then allowing air exchange only through the designated air exchanger. when i build my dream house i want it to be able to hold a vacuum when the exchanger is blocked off. 

from what i have studied i have come to the conclusion that any air or moister entering or exiting from anywhere besides a open window, door, or air exchanger is just shoddy workmanship fancied up by calling it "breathing"


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## NorthwoodsMike (Jun 10, 2013)

fullmetal said:


> i very firmly believe in sealing all exterior surfaces (walls, roof, windows, etc) to a hermetic level, and then allowing air exchange only through the designated air exchanger. when i build my dream house i want it to be able to hold a vacuum when the exchanger is blocked off.
> 
> from what i have studied i have come to the conclusion that any air or moister entering or exiting from anywhere besides a open window, door, or air exchanger is just shoddy workmanship fancied up by calling it "breathing"



So you plan to exchange the air between the studs? If not, how do you intend to deal with wood off gassing? If they are "hermetically sealed," your walls may rot from the inside out.

I know what you are saying about breathing, but your talking about something different. With an inner wall vapor barrier, you will hold a vacuum like you want. With an outer moisture barrier, the studspace can breathe, which you want. That is a good type of breathing, and reflects good workmanship.


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## Clod Kicker (May 7, 2012)

It is impossible to hermetically seal a wood framed structure.


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## Clod Kicker (May 7, 2012)

It is impossible to hermetically seal a wood framed structure!
Unless one sprays foam in a continous fashion.


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## evan (Dec 24, 2013)

Spray foam insulation makes a great vapor barrier. By the time you add up the cost of vapor barrier and electrical boxes with gaskets tape for the seams fiberglass batting and your time it's totally worth it to have someone come in and spray it


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## NorthwoodsMike (Jun 10, 2013)

evan said:


> Spray foam insulation makes a great vapor barrier. By the time you add up the cost of vapor barrier and electrical boxes with gaskets tape for the seams fiberglass batting and your time it's totally worth it to have someone come in and spray it



Closed cell foam does. Google what happens when open cell comes into contact with water. My fear is moisture in vapor form would do the same, just take longer.

I priced out both types of foam for my build, both cost at least 2x as much, and that was padding the alternatives quite a bit, including labor. I think where one lives affects the cost to the consumer. Where I live, there were very few competitors. It's worth looking at anyway.


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## Clod Kicker (May 7, 2012)

When using closed cell rigid foam or sprayed in, a vapor barrier isn't necessary. The vapor barrier is to prevent the insulation from getting saturated from household activities; like cooking, bathing, and sobbing about the oil bill. :Bawling: Therefore the VB always faces the conditioned space.


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## evan (Dec 24, 2013)

I just spray foamed the farm house we are redoing. Its about 3500 square feet, 3 levels and the ceiling upstairs with 3 inches and it was about 7k just for a reference.


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## NorthwoodsMike (Jun 10, 2013)

evan said:


> I just spray foamed the farm house we are redoing. Its about 3500 square feet, 3 levels and the ceiling upstairs with 3 inches and it was about 7k just for a reference.



I'm jealous. Just under 3000 sqft, 3 levels with half walls in basement and cape cod style walls upstairs was 10k ish for open cell. I think 12k for closed. Fiberglass was $2500 for all material(sale) and 1k for install. It was an easy decision for me.


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## MichaelZ (May 21, 2013)

You never want to put plastic under exterior siding in cold winter locations. The plastic will trap moisture inside your walls leading to rotting and extensive mold. Our neighbors had such a house and they ended up selling for the value of the land only and the buyer demolished the house. In cold winter locations you put the vapor barrier on the heated side of the insulation, right under the interior finishing material or drywall. And we always tape the seams of the barrier to make it air tight. You want virtually none of the interior moisture getting into the insulation where it can condense out. On the outside under the siding a breathable house wrap is used. And I am referring to a fiberglass bat insulation. For sprayed on foam, the foam itself creates the vapor barrier as it seals up everything pretty air tight.


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## fullmetal (Nov 2, 2013)

NorthwoodsMike said:


> So you plan to exchange the air between the studs? If not, how do you intend to deal with wood off gassing? If they are "hermetically sealed," your walls may rot from the inside out.
> 
> I know what you are saying about breathing, but your talking about something different. With an inner wall vapor barrier, you will hold a vacuum like you want. With an outer moisture barrier, the studspace can breathe, which you want. That is a good type of breathing, and reflects good workmanship.


true, thats why i dont like wood stud walls. However fully dried studs (not the half green stuff you see now days) will still be just fine sealed on both the inner and outer walls.
that being said steel or masonry is a better choice if both sides are going to be sealed. finally if you were planing to seal both sides of the wall it would make sense to add some desiccant to the area before sealing to take care of whatever tiny amount of moister you failed to remove. 
more than just moister or air this double sealing creates a better heat barrier which significantly improves your insulation values sometimes as much as 200%

finally as others mentioned closed cell foam is a excellent air and vapor barrier.


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## NorthwoodsMike (Jun 10, 2013)

fullmetal said:


> true, thats why i dont like wood stud walls. However fully dried studs (not the half green stuff you see now days) will still be just fine sealed on both the inner and outer walls.
> that being said steel or masonry is a better choice if both sides are going to be sealed. finally if you were planing to seal both sides of the wall it would make sense to add some desiccant to the area before sealing to take care of whatever tiny amount of moister you failed to remove.
> more than just moister or air this double sealing creates a better heat barrier which significantly improves your insulation values sometimes as much as 200%
> 
> finally as others mentioned closed cell foam is a excellent air and vapor barrier.


How are unexpected things like rodents/insects dealt with? Many times, they bore holes, and water follows. In typical construction, the hole can be sealed, and water can escape through the barrier. I'm curious how it is handled with fully sealed walls, now that moisture is introduced.

I don't dispute it has it's advantages, I'm just skeptical that it is the best solution, and that everything else is poor workmanship-guess that kinda rubbed me the wrong way.


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## fullmetal (Nov 2, 2013)

NorthwoodsMike said:


> How are unexpected things like rodents/insects dealt with? Many times, they bore holes, and water follows. In typical construction, the hole can be sealed, and water can escape through the barrier. I'm curious how it is handled with fully sealed walls, now that moisture is introduced.
> 
> I don't dispute it has it's advantages, I'm just skeptical that it is the best solution, and that everything else is poor workmanship-guess that kinda rubbed me the wrong way.


you make another good point. for this type of building it would be important to make it very rodent/insect resistant/repellent with things like wire lath and such so that they dont damage the walls in the first place. however the very effort to make it air tight often discourages them without any extra planning since not much will chew through a few inches of closed cell foam and its cladding without a really good reason. 

even if they did make a hole sealing it up again when you found it should be enough assuming no massive water flow occurred. if a large amount of moister was introduced to the interior of the wall it could be handled by creating a small hole and adding a fine desiccant and re sealing depending on the damage. but any wall (no mater what the construction style is) could be damaged if enough water finds its way in faster than it can escape which might happen if water was flowing into a mouse hole.

as for the "this is the only way" line i should apologize. sorry about that. i was just really sick of contractors, builders, and random internet people insisting that wind whistling through the electrical outlets and window frames is the house "breathing" and that it _needs_ to be that way 

the whole idea behind this kind of wall is that instead of building it with a way out for water that is likely to get in, put that effort into making sure that water never gets in in the first place.


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## NorthwoodsMike (Jun 10, 2013)

fullmetal said:


> you make another good point. for this type of building it would be important to make it very rodent/insect resistant/repellent with things like wire lath and such so that they dont damage the walls in the first place. however the very effort to make it air tight often discourages them without any extra planning since not much will chew through a few inches of closed cell foam and its cladding without a really good reason.
> 
> even if they did make a hole sealing it up again when you found it should be enough assuming no massive water flow occurred. if a large amount of moister was introduced to the interior of the wall it could be handled by creating a small hole and adding a fine desiccant and re sealing depending on the damage. but any wall (no mater what the construction style is) could be damaged if enough water finds its way in faster than it can escape which might happen if water was flowing into a mouse hole.
> 
> ...


Do you think it's worth it though? That's alot of extra material upfront, alot of extra work later on, and if something isn't done right, it's alot less forgiving. You will have gains in efficiency, but I personally would rather pay a few extra pennies a month and have things more "automated" if something small goes wrong.

I definitely respect that you don't want to cut corners though. Too many people don't have that attitude, and pay for it later.


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## fullmetal (Nov 2, 2013)

for me at least i think yes it is worth it, it is extra work/extra material/less forgiving but the gains (thermal, and life of materials) if done right are enormous. especially if that attitude is applied to the whole house from the start not as a retrofit. 

just as a example there is a family i talked to in north west montana that in the last decade has never heated their house as it was so well built and insulated that the heat gains just from being present in the house keep it warm. but it cost a small fortune so to each his own


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## barnyardgal (Sep 21, 2009)

Is the sprayed on insulation best to use especially in new home construction?? guess the R-factor would be better & make for a better air seal??


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## fullmetal (Nov 2, 2013)

barnyardgal said:


> Is the sprayed on insulation best to use especially in new home construction?? guess the R-factor would be better & make for a better air seal??


i think the closed cell spray foam is good but too expensive to use by itself. for new construction i would go with a very cheap insulation (like cellulose or fiberglass) for the bulk, like 5 or 6 inches then one inch closed cell foam sprayed over it. 

even better would be a "sandwich" with one inch foam, several inches cellulose, then one more inch foam. it would have all the air and vapor tight advantages of foam insulation while saving a lot of money every inch and a half or the sealed cellulose is the same as 1 inch of closed cell foam.

so in a 12 inch thick double wall construction with one inch foam on each side of 10 inches of cellulose comes out to about r-63 plus 2 to 7 for the dry wall and outer wall materials. so r-65 to r-70


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## Cathy Science (Feb 18, 2014)

Dear Bubba Boys and Oldfashiondad, 

You are correct, DuPont&#8482; TyvekÂ® is not a vapor barrier. The material is engineered to keep air and bulk water out while allowing moisture vapor inside walls to escape. Here&#8217;s a link to more information: http://www.dupont.com/products-and-...ls/building-envelope-systems/faqs/wb-faq.html 

(Cathy is a member of DuPont and is posting this just to clarify what the product is used for. She is not advertising. I verified this.)


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## fishhead (Jul 19, 2006)

It looks like someone would come up with a spray on vapor barrier.


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## gjensen (Feb 8, 2014)

There is spray or roll on air/moisture barriers. They are frequently used on commercial buildings. If you do not mind the cost, they are more effective than commonly used barriers.

It certainly advisable to use an exterior vapor/moisture barrier to protect the structure, while exterior finish is maintained responsibly. 

There is a number of assemblies that can be used to satisfy any concern or be based on a number of theories. Then your climate, micro climate can be a consideration. 
An example is I used taped rigid insulation over sheathing and a vapor barrier on my exterior. My theory s that heat is a larger factor here than the cold is. By insulating the structure, I cut down on how much the structure is heated, and how much heat it releases. 

My roof s slatted with 2"x, and the sheathing installed on top. In the attic, I nailed rigid insulation (1/2") to the slats. This cuts down on ho much the attic space is heated. It has made a difference. 

Whether or not the insulation is used with the vapor barrier out or in generally depends on your climate. 

Wood continues to dry when the building space is conditioned. That is what causes much of the drywall nail pops. Some of it structure movement of course. 

Modern building science s based on the building being heat and cooled all of the time. If the humidity in the house is allowed to stay on the higher side for lengths of time, structure ventilation is a consideration. 

Old houses in the south were not insulated, and their framing method let the walls draft. They were indeed less prone to moisture and mold.


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