Wrapping walls with plastic before drywall??

[K588]

I have a 40' x28' with 10.5' ceiling height 2 story gambrel style barn I built. It is stick framed with 2x6 walls 16oc. I am in the process of installing R19 kraft faced insulation. the outside of the walls is T111 no tyvek wrap etc.

I live in Maryland where it can be over 100 and humid in the summer and sometimes the single digits in the winter. My question is whether or not I should put plastic up over the insulation before I install the 5/8" drywall. The building will have heat and AC eventually.People I talk to and the things I have read on the net seem to give conflicting info, any help is appreciated.

 

[Junkman]

I did, and I have not had any negative problems, and it is over 30 years ago that I did it. If you are doing the drywall yourself, you can use 3/8" drywall, and then go over it with a second covering of 3/8" and have a very solid wall. I had mine installed, and it is all 5/8" fire code rated. Just remember, that the ceiling goes up first, and the last piece to go on is at the floor, if you lay it sideways. I used plastic on the ceiling also, and strapped the ceiling afterwards with 1" x 2" furring strips before the sheet rock. Everything is screwed, and there are no nails.

 

[galute]

I'm going thru the same thing right now trying to figure out how to finish out the inside of my pole barn. Everything you read or everyone you talk to has a different opinion. Vapor barrier on inside, vapor barrier on outside, no vapor barrier. UUggghhhh!!! It was making me crazy. I finally called the guy who built my shell yesterday and asked him. He asked me if I had ever been in an insulated shop. I said yep, hundreds of them. He then asked how were they built? I said they put wide rolls of insulation with plastic covering to the inside then screwed the tin directly over that. Dooooaaahhhhh!!!! He just laughed and said you're trying to make it too complicated. LOL

 

[Kevin54]

Back years ago, it was always said to NOT put a plastic vapor barrier over the insulation before hanging drywall or whatever material you decide to hang, as it would cause the room or building to act like a greenhouse. The experts slowly started going the other way and said it was perfectly fine to cover everything in plastic. Then in recent years the experts say that to do it correctly, you cover the complete inside walls with plastic AND make sure everything, meaning every seam, is taped to stop any air infiltration completely and using extra care around outlet boxes and switch boxes.

If you watch any of Mike Holmes remodels, he puts plastic on all of his inside walls and uses the red tape (whatever it is) to tape all of his seams.

So I would say today, covering the inside of the outer walls is acceptable if not highly recommended.

 

[dos zetas]

A lot depends on where you live- in a desert with big temperature fluctuations between day or night, or in the midwest where a heated building keeps the temps even all winter.
Mold infestation is a serious thing, you are smart to be doing research on this before you build.
Maybe there is a county ag extension office or a engineering college near you that can give you good info for your climate.

 

[Thumper68]

If you are using kraft faced insulation you don't need a extra vapor barrier, The kraft facing is the vapor barrier. If using un faced witch would be my recommendation then you put the vapor barrier over that and use the tape to seal all seams, around all the boxes etc..

 

[TXDego]

I would highly recomed not using plastic, that is a good way to grow mold. Plastic does not have the ability to breath, it will trap moisture, and promote condensation. This was a very big deal here in Texas, lots of law suits over this.

I would recomend, that if you wanted a vapor barrier, to use 30lb felt. This works great, is fairly inexpensive, and it allows your walls to breath.

Good luck!

 

[Ross/Kzoo]

Maybe there is a county ag extension office or a engineering college near you that can give you good info for your climate.

With so much dependent of local conditions I would do as dos zetas advised.

 

[2CRUZ]

I used both on my 30x40 garage build. I used Tyveck on the out side under the ceder sideng then I used heavy mill plastic on the inside under the sheet rock. It's been two years and no problems at all and it doesn't take 10 minutes for it to warm up in the winter.

 

[CNGsaves]

Welcome to GJ. Sounds like you have nice sized shop. Before this thread gets too far, now would be a good time to Update GJ Profile with your Location.

Let's SEE some pictures as they tell a thousand words.

 

[SARG]

When they mass produce mobile homes they wrap the entire inside with the plastic before any interior surfaces are finished ... so essentially it is like living inside a wrapper for a loaf of bread.

Keeps the heat and moisture on the inside .... and the cold on the outside.
Also why we need to run a dehumidifier every winter.

 

[robr2]

The general rule is to avoid double vapor barriers. The kraft paper acts as one and the plastic acts as the other.

The issue is that any moisture that gets through one may not get through the second and condense between them. Neither one of them is 100% impermeable so I would avoid doing both.

YMMV

 

[willymakeit]

Back years ago, it was always said to NOT put a plastic vapor barrier over the insulation before hanging drywall or whatever material you decide to hang, as it would cause the room or building to act like a greenhouse. The experts slowly started going the other way and said it was perfectly fine to cover everything in plastic. Then in recent years the experts say that to do it correctly, you cover the complete inside walls with plastic AND make sure everything, meaning every seam, is taped to stop any air infiltration completely and using extra care around outlet boxes and switch boxes.

If you watch any of Mike Holmes remodels, he puts plastic on all of his inside walls and uses the red tape (whatever it is) to tape all of his seams.

So I would say today, covering the inside of the outer walls is acceptable if not highly recommended.

The red tape is the same as EFIS system tape. Sticks good.

 

[Angelfire]

Deciding on the required permeability of your wall system is very much dependent on your climate, materials, etc...

What works for one person here may not work for you. Typically, many will recommend just putting visqueen up before the sheetrock. In some cases, this makes sense. But in many others it does not. You want a wall that allows vapor to exit should the cavity get wet....visqueen doesn't do this. Here is some "light" reading on the subject that I found to be very useful when I built an addition on my home:

http://www.buildingscience.com/documents/reports/rr-0412-insulations-sheathings-and-vapor-retarders

I ultimately went with a variable vapor retarder with no complaints other than it's a bit of a pain to ensure it's completely sealed everywhere.

Cheers.

 

[icenfire01]

If you are using kraft faced insulation you don't need a extra vapor barrier, The kraft facing is the vapor barrier. If using un faced witch would be my recommendation then you put the vapor barrier over that and use the tape to seal all seams, around all the boxes etc..

Why not kraft faced, it sounds like it will eliminate the need for plastic thus saving a step. I also like the idea that by stapling it to the studs it insures that the insulation does not settle over time. Ive been in a lot of homes where there is a 3 or 4" air gap at the top of the walls from gravity pulling down on insulation over the last 30-40 years.

 

[GYPSY400]

In cold climate.. the norm is to use standard plain pink batts and vapour barrier the inside wall.. taping the seams and electrical boxes as well as acoustics seal the triple studs etc. to completely seal the inside (zip lock bag effect )..

Think less about vapour and more about barrier.. the vapour will be on the warm side, so you need to barrier it away from the insulation to keep it dry.. wet pink batts don't work.

you want to avoid 2 vapour barriers ( either kraft paper or close cell foam) as this promotes condensation.


I'm currently at this stage in my build.


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[Moss]

How you insulate is very climate dependent and I only know what works in my climate here in Ontario Canada and I don't think it's that much different then Maryland. Our building code requires a "vapor barrier" directly behind the drywall. The logic behind it is the warm air from the heated space moves through the wall. When the warm air reaches the colder air in the wall cavity the moisture in the air forms into droplets creating a very bad situation inside the wall cavity that causes mold and rot issues. The vapor barriers we build here are poly plastic on walls and electrical outlets, acoustic caulking and red "tuck tape" where needed. This ideally forms a complete seal that doesn't allow the air to pass through the wall cavity and works very well when installed properly. It also seals drafts really well.

I agree with robr2 that having double barriers is a bad scene. I am not sure how well the kraft backed insulation would really work for this purpose. It is not sold here anymore to my knowledge but I have seen it when doing renovations on older homes with the paper facing inside the home and usually tar paper on the outside of the walls.

*I think Gypsy400 posted the same basic info above me before I hit send *

 

[GYPSY400]

How you insulate is very climate dependent and I only know what works in my climate here in Ontario Canada and I don't think it's that much different then Maryland. Our building code requires a "vapor barrier" directly behind the drywall.
The vapor barriers we build here are poly plastic on walls and electrical outlets, acoustic caulking and red "tuck tape" where needed. This ideally forms a complete seal that doesn't allow the air to pass through the wall cavity and works very well when installed properly. It also seals drafts really well.

I agree with robr2 that having double barriers is a bad scene. I am not sure how well the kraft backed insulation would really work for this purpose. It is not sold here anymore to my knowledge but I have seen it when doing renovations on older homes with the paper facing inside the home and usually tar paper on the outside of the walls.

*I think Gypsy400 posted the same basic info above me before I hit send *

That's true.. older house's have Kraft paper.. I've never seen it for sale Locally while shopping for supplies recently... And I'm also shopping in Ontario Canada. But like you said, building code depends on region.



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[Krodad]

How far into the process are you with the paper faced batts?

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[PCO6]

I can't remember the last time I saw paper backed insulation. As said, a poly vapour barrier is pretty much the standard here. My garage became "almost" air tight after I taped the vapour barrier seams. I don't see how that is possible with paper backed insulation. I'm sure products are sold based on what the local codes are though which makes sense.

Here's how I did mine - drywall on the walls and a metal ceiling ...
View media item 36427

 

[Moss]

What does the building code say in your area? I found some info that it is the same as here in Ontario but it was county based not state.

I will also add that old structures I have ripped into that use the kraft paper inside/tar paper outside have shown little mold problems in regard to the insulation. Most issues related to rot and mold in the ones I have seen are related to actual water leaks in the structure usually around windows or at the sill plate of garages that didn't get graded properly.

 

[Dale Leeds]

I did, and I have not had any negative problems, and it is over 30 years ago that I did it. If you are doing the drywall yourself, you can use 3/8" drywall, and then go over it with a second covering of 3/8" and have a very solid wall. I had mine installed, and it is all 5/8" fire code rated. Just remember, that the ceiling goes up first, and the last piece to go on is at the floor, if you lay it sideways. I used plastic on the ceiling also, and strapped the ceiling afterwards with 1" x 2" furring strips before the sheet rock. Everything is screwed, and there are no nails.

If you put furring strips on the ceilings, didn't that make the walls less than 8 feet? And if you did that, you'd have to cut an inch or so off of the drywall that is going on the walls. Why didn't you just screw your drywall to the ceiling beams?

 

[yfz 450]

I am a carpenter by trade in southern n.y. All we do when building a house is tyvek paper on the exterior of the sheathing and paper back fiberglass insulation on interior.

 

[Moss]

I am a carpenter by trade in southern n.y. All we do when building a house is tyvek paper on the exterior of the sheathing and paper back fiberglass insulation on interior.

Perfect example of how codes and overall building philosophies can be different even though we are really aren't that far away geographically. I am not one of those "you should build it to code" people in all circumstances but if in doubt I would humbly suggest following code for your area.

 

[MrMark]

This really is a simple matter. The general rule is that plastic visqueen type barriers are to be avoided unless you live in an extremely cold climate like Alaska or Canada or Montana. Warm moist air moves through a wall assemble and will condense on the first cold structure that it finds. The vapor barrier on the inside works in these extemely cold regions because they are heated on the inside predominantly. Mike Holmes is not someone to emulate for most of the US as he is dealing with frigid climate.

If you have AC and you have that vapor barrier on the inside you just created a disaster. The warm moist air from the outside moves right through the tyvek and hits the cold dry inside edge of that plastic barrier on the inside and condenses in the wall.

Unless you live in a frigid climate and have no AC you shouldn't have any vapor barrier at all. Vapor barriers are to be avoided in general and only vapor retarders should be used according to your climactic zone and whether you are going to use AC as well as heat. In Maryland with the plans for AC of the OP he probably should use no more than kraft faced insulation.

Here in SoCal we would use unfaced insulation. The idea is to not trap moisture and if any gets in to allow the wall to breathe to dry out.

 

[Moss]

This really is a simple matter. The general rule is that plastic visqueen type barriers are to be avoided unless you live in an extremely cold climate like Alaska or Canada or Montana. Warm moist air moves through a wall assemble and will condense on the first cold structure that it finds. The vapor barrier on the inside works in these extemely cold regions because they are heated on the inside predominantly. Mike Holmes is not someone to emulate for most of the US as he is dealing with frigid climate.

If you have AC and you have that vapor barrier on the inside you just created a disaster. The warm moist air from the outside moves right through the tyvek and hits the cold dry inside edge of that plastic barrier on the inside and condenses in the wall.

Unless you live in a frigid climate and have no AC you shouldn't have any vapor barrier at all. Vapor barriers are to be avoided in general and only vapor retarders should be used according to your climactic zone and whether you are going to use AC as well as heat. In Maryland with the plans for AC of the OP he probably should use no more than kraft faced insulation.

Here in SoCal we would use unfaced insulation. The idea is to not trap moisture and if any gets in to allow the wall to breathe to dry out.

Not trying to argue Mark but we almost all have AC up here and our average summer average highs are in the 80's and very often it gets into the 90's. We have no issues with our system in the summer months. But our air is not dry it's very humid. I'm not saying what we do up here is "right" it does work in my experience when done properly though.

In my opinion It's actually a fairly complicated matter with different practices in place all over the USA and Canada dependent on what conclusions building officials determined would work best in there region. That's apparent by the different solutions and ideas offered in this thread. Hence I recommended him to follow his local building codes if unsure.

 

[MrMark]

I question how well that Canadian system works then if you have AC running in the summer. The science is not subject to dispute. Warm moist air vapor will travel to try to reach the cold dry air because of the pressure differential. In the summer moisture will condense on the inside of the plastic if AC is running UNLESS you have a double barrier where you also install a vapor barrier (not Tyvek as Tyvek is vapor permeable to breathe) on the outside too. What do you have on the outside? Do you double barrier the walls in Canada?

Building codes are not really helpful on something like this. Look at all the moisture and mold problems in FL and Texas and other places because of lack of understanding of basic science.

To show you how far codes and construction practices lag behind the forefront of thinking on this subject, you cannot even buy unfaced insulation here in SoCal as a stock item. It has to be special ordered even though all Building Science type articles and studies show that we should use unfaced here. Latex paint is enough of a retarder for our area.

 

[MrMark]

I just found this article on the subject.

http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/reviving-old-debate-vapor-barriers

Doesn't Holmes spray foam every house he works on? I stop watching Holmes because I never learned anything from his shows. Besides bagging on contractors, all he talks about is insulation and vapor barriers and it is all irrelevant to someone who doesn't live in a freezing climate. The little ear ring is cute though.

That spray foam is also a vapor barrier isn't it? If so, then you get double barrier walls in Canada. You would really need to have a perfect assembly for this to work because what does get in is not getting out.

 

[PCO6]

I was a land developer for the last 25 years before I retired earlier this year. I wasn't sure about the best way to insulate my garage so I asked a few of our home builders. Each of them said it should be done they same as the houses they built ... basically the way I show in post #20.

A lot of our projects were in the City of Markham which abuts Toronto. The link below is from the Markham Building Department and is in regard to insulation inspections. It includes a builder's checklist to assist in reducing Ontario Building Code (OBC) deficiencies. I pretty much followed the last inspection point.

http://www.markham.ca/NR/rdonlyres/4EB1A0A0-EB4C-4214-B47F-D300CC8F7315/0/Insulation.pdf

 

[bullnerd]

I can see the condensation in the cold from an inside heat source. But can an inside AC source really get the inside surfaces cold enough to produce condensation on the outer surface of the inside plastic during summer?

 

[MrMark]

All I know from reading many articles about this is that a plastic vapor barrier is to be avoided for all but the most frigid climates. If you notice you will see that most of the posters with the visqueen are Canadian. The articles say that the visqueen phenomena is an arctic weather artifact. You have to have so many (read a lot) "heating days" to even be thinking about a vapor barrier.

Even in the arctic zones, the articles are adamant that if you insist on visqueen for your air and vapor barrier then you cannot air condition the building.

Maryland is not Canada and he said he wants to run AC so the OP is getting lots of bad advice in this thread.

 

[bullnerd]

So what did you decide OP ?

After reading the articles MArk posted it looks like you should be fine with just the paper faced batts. Since you are using drywall that will be your air barrier and if you paint with latex that will be your vapor retarder.

I would like to find more info on this subject more related to metal clad buildings, inside and out, as that is where I am currently with my building. I guess I have to look into some of these more modern vapor retarders that are mentioned.

 

[Milton Shaw]

Once you get a vapor/air movement barrier, then you don't get as much air movement to cause vapor to condense on the cold vapor barrier inside. I would think that house wrap outside with vapor barrier/air flow restriction inside that the moisture build up would not happen. Its when you have air flow that you carry moisture in with the air.

 

[PCO6]

Not trying to argue Mark but we almost all have AC up here and our average summer average highs are in the 80's and very often it gets into the 90's. We have no issues with our system in the summer months. But our air is not dry it's very humid. I'm not saying what we do up here is "right" it does work in my experience when done properly though.

Anced - I'm not sure where you are in Canada but that pretty much describes my situation. As for the OP, or anyone, it's usually best to check with the local building department, contractors, suppliers, etc. or go with the codes that apply.

 

[bullnerd]

http://www.youtube.com/watch?feature=player_embedded&v=mlbBctombI0

 

[larry4406]

The OP is in Maryland. I build houses in Maryland and Va for a large production home builder.

From the outside in we have: siding, house wrap (tyvek), 1/2" OSB, 2x6 framed walls, r21 insulation, caulk air seal on all framing, Kraft paper, drywall, and paint.

Our homes are Energy Star and HERS rated homes. I asked our rater about plastic vapor barrier. His response was never in our zone. Kraft paper only for our zone.

 

[tcianci]

After reading all of these posts, it's obvious that most of the people who commented are WAY off in their science. Mr Mark is the flat out winner as far ad bad science is concerned.

No one has even touched on the purpose of a vapor barrier or vapor retarder. Understanding the purpose of the barrier would go a long way in understanding whether or not to use it and what type to use.

A vapor barrier or retarder's sole purpose is to prevent or reduce the transmission of water vapor that originates within a structure into the insulated cavity, where given the right temperature and humidity conditions, the vapor could condense into liquid water and cause a temporary reduction in the rated performance of the insulation product. The reduction is temporary because when the conditions inside the wall become favorable for the evaporation of the liquid water, the insulation re-gains it's performance. Note that the vapor barrier or retarder (which I believe to be a better term) on kraft faced insulation is applied by the insulation manufacturer and it is done specifically to protect the performance of the insulation product, and is not intended for mitigating drafts or more minor air infiltration. That's the reason some builders install unfaced insulation products followed up by a polyethylene sheet before drywall. This type of installation can provide both vapor retardation and draft mitigation, although draft mitigation is best accomplished on the outside of the building, as limiting air flow in the insulated cavity provides better thermal performance, at the expense however, of the service life of the structure

I realize that in an effort to build "perfect" structures, the theology of where and how to insulate gets hotly contested. It is strongly suggested to defer to the manufacturers instructions for the insulation product you're using. In general however, the most common practice is to apply the vapor barrier toward the conditioned space.

It would be helpful for Mr Mark to explain the origin of the "pressure differential" that he claims causes hot moist air in the summer to move into and through a wall structure until it condenses behind the vapor barrier.

After over 40 years of building and remodeling in Massachusetts where we commonly get temperatures in the 80's to 90's with very high humidity, I have never once seen an example of a condensation issue due to air conditioning.

 

[PCO6]

... A vapor barrier or retarder's sole purpose is to prevent or reduce the transmission of water vapor that originates within a structure into the insulated cavity, where given the right temperature and humidity conditions, the vapor could condense into liquid water and cause a temporary reduction in the rated performance of the insulation product...

That's basically it as far as I understand. Keep the warm air in. I pretty much sealed my garage from the inside with 6mm poly and taped the seams. The warm air never meets the insulation. I live in Southern Ontario - YMMV.

 

[bullnerd]

"I have never once seen an example of a condensation issue due to air conditioning."- this is basically what I was asking.

 

[Autorotica]

Forgive my ignorance, but I thought the issue is vapor barrier (not retarder) on both sides of the insulation. That creates a space where IF vapor gets in there it cant get out...

If you have plastic on the inside and a permeable membrane on the outside, the moisture can always move OUT as it has opportunity.

The other point, is there a vacuum sucking the outside air into the building? Fiberglass insulation make a great dirt filter but it doesn't stop air from moving. Where is all this WIND coming from that is placing so much entrained vapor against a surface?

Chris