Wall and Ceiling Vapor Barrier

[Mark100]

Hello,

I am researching ceiling options for my garage. It will be a 1000sq.ft. heated detached garage in South East Michigan with good insulation (R-19 walls, R-49 blow-in in ceiling). I am leaning towards either drywall or the metal paneling. It seems like there is information for and against installing a vapor barrier in the ceiling while using drywall or metal panels. I have read that painted drywall will act as a vapor barrier and I can see that metal could also have similar properties. I am still undecided on what would be the best route with regard to the VB.

I don't see as much debate with vapor barrier on walls. I will most likely drywall and paint the walls and I had planned on using faced batts. Wouldn't the same "paint as a vapor barrier" idea hold true with walls? Why would walls require a VB and not the ceiling with this argument? What am I missing?

Thanks,
Mark

 

[Kaizen]

I’m putting up a 6 mil for the heck of it in the ceiling. I don’t want water drips or marks. One thing to consider is in ceiling it will contact substrate immediately but a wall has the chance of running down first due to gravity. I would not call drywall a barrier. Painted or not


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[Jlbc212]

I used 6 mil over the insulation on my walls and ceiling (drywall on the walls and metal ceiling) - no regrets. I agree with Kaizen, I also do not consider drywall, painted or unpainted, as an adequate vapor barrier.

 

[Andamo]

Look on You Tube for a series called R&R Buildings. Kyle builds pole barns mostly in central Illinois and for the ceilings he puts plastic on the rafters and then corrugated metal ceilings. He subcontracts the insulation of the building but it's usually blown in fiberglass above the plastic.

 

[Mark100]

Did you use faced or unfaced insulation in the walls?

I used 6 mil over the insulation on my walls and ceiling (drywall on the walls and metal ceiling) - no regrets. I agree with Kaizen, I also do not consider drywall, painted or unpainted, as an adequate vapor barrier.

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[Paxtonshelby]

Look on You Tube for a series called R&R Buildings. Kyle builds pole barns mostly in central Illinois and for the ceilings he puts plastic on the rafters and then corrugated metal ceilings. He subcontracts the insulation of the building but it's usually blown in fiberglass above the plastic.

Watching Kyle’s vids will answer all your questions and more. I wish he was closer to my area - I’d love to have him build my dream shop in a few years. I actually have one of his videos up on my phone right now.

 

[yeldogt]

The key with any building is ....drying. You have to build in a way that a building will dry -- one must be very careful using plastic VB. It's impervious .... what you are trying to achieve is a vapor retarder.

Craft facing is not a full barrier. That's why building wrap is also vapor permeable.

When you create a barrier there is always the danger of having a condensation issue when outside air is humid and a garage is colder .. this can happen often throughout the year.

It all about drying .... I would use one o the newer VB products available.

Most people have no idea what happening inside the wall ... until the damage from rot shows. When Plastic was first used back in the 70's -- it took 10 -15 years to show up as a big problem.

Initially .... plastic seems great. It's acting not only as a VB ... but also sealing from leaks. As taps and caulk fail .. buildings move and gaps start moisture gets trapped.

The same thing can happen when spray foam is sprayed really thin .. under an inch. Although because it typically never allows leaks .. the air flow moisture problem is less.

 

[Marctrees]

Walls are the same as ceilings re vapor barrier.

Sheet steel is an excellent vapor varrier, as long as its made decently air tight at the wall/ ceiling meeting.

As far as the seams in the field go, IMO it would be overkill to use the butyl tape or anything there but you certainly could.

Read below... Post# 4 The second article goes on forever, but at least understand the first article.

Marc

https://www.garagejournal.com/forum/showthread.php?t=438935

 

[BruceMc]

The key with any building is ....drying. You have to build in a way that a building will dry -- one must be very careful using plastic VB. It's impervious .... what you are trying to achieve is a vapor retarder.

Not in a cold climate you don't. You want a vapor barrier on the warm side so it stays dry in the first place. If warm, moist air gets into a cold wall, you will get condensation where the temperature reaches the dew point, and eventually you can wind up with mold and rot. If it's below freezing outside, the moisture in the wall will freeze at that point in the temperature gradient in the insulationn, and the freezing and dew point will move ever closer to the inside wall.

Anyone that's ever been cold weather camping and tried keeping their face buried in their sleeping bag understands what happens to cold insulation exposed to warm, moist air.

 

[Marctrees]

Yup, BruceMC did pretty good to explain it - if you Goggle "Insulation Condensation Plane" and find the REAL TECH articles and wade through the BS sites, you will learn and understand.

Marc

 

[Marctrees]

Be aware, there are situations where the Kraft paper is slashed w a sharp razor knife like maybe every six inches x full width to NOT create a "Second VB"

Properly installed Kraft face FB is NOT as good a VB as covered w taped Poly...

BUT...

But...

With the newer smarter studied Scentific thinking it is often sufficient.

Again, VERY important - As the recent ?20? yrs years go by and study of Mold, VB permiance and placement is being studied and recommendations morphing.

Current think summarized - In ROUGH terms ... S border of Iowa nd N of there install
FYLL VB inside side of the Insul.

Jumping to Southern Hot/ Humid... VB is installed OUTSIDE the insul.

In Geo areas in between the two extremes...

It is still being debated... but loosly speaking the VB is less mandated than 20 yrs ago in those "Mid" geo areas.

Gotta study to understand.

Do NOT listen to me, READ the "White Paper" stuff.

Marc

 

[Marctrees]

I really feel I have done a good job answering this.

Marc

 

[matt_i]

Imo for a garage you have to ask yourself where all of the moisture is coming from? (washing cars indoors, cooking, showering, running non-vented heaters indoors are some common sources). If you don't do any of those its basically coming from outside-ambient.

Also imo more important than vapor barrier is air sealing, as that's the conveyance for warm moist air to cold surfaces. Reduce that dramatically and the internal moisture collection & concentration can't happen.

It seems to me like vapor barriers in a garage where you aren't actively "generating humidity indoors" are a stop gap solution that's cheaper and faster than detailing actual air sealing.

If you do drywall you also cannot adhere it with adhesive effectively. I would use more screws than typical if you go the plastic route.

 

[Jlbc212]

Did you use faced or unfaced insulation in the walls?

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I used unfaced fiberglass insulation in the walls and the ceiling.

I've opened up walls after twenty years that had fiberglass insulation with a plastic vapor barrier on the interior side of the building and haven't found mold.

I'm not sure how matt_i intends to achieve "air sealing." As soon as you open a door you have broken an air seal. There's is always some amount of moisture in the air in the form of invisible vapor. An extreme cold or desert climate may have a negligible amount of moisture in the air, but you will notice the lack of moisture as you attempt to breathe.

 

[Mark100]

Thanks for all the info. I will talk to my building department to see what they require and then make my decision.

Is there any negatives for using metal rib panels on the ceiling vs drywall? The only ones I can think of are some echoing and fire barrier.

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[yeldogt]

Not in a cold climate you don't. You want a vapor barrier on the warm side so it stays dry in the first place. If warm, moist air gets into a cold wall, you will get condensation where the temperature reaches the dew point, and eventually you can wind up with mold and rot. If it's below freezing outside, the moisture in the wall will freeze at that point in the temperature gradient in the insulationn, and the freezing and dew point will move ever closer to the inside wall.

Anyone that's ever been cold weather camping and tried keeping their face buried in their sleeping bag understands what happens to cold insulation exposed to warm, moist air.

You missed my point .... it's about proper insulation. You can get plenty condensation with plastic VB ... it's what caused all the problems back in the 70's and 80's when it was used. Plastic will not allow a building to dry when the condition occurs. Craft VB and all the new sheet type allow for drying .. slow moisture travel .. drying.

Not having enough insulation -- or leaks that allow moist air to travel through walls is the problem .. all made greater with plastic

 

[yeldogt]

I really feel I have done a good job answering this.

Marc

except if you look at the current thinking and the experience of many years -- plastic is not the way to go. Add in the new taped exterior .... Especially the zip walls -- now you have a sealed cavity .. not good.

 

[yeldogt]

I used unfaced fiberglass insulation in the walls and the ceiling.

I've opened up walls after twenty years that had fiberglass insulation with a plastic vapor barrier on the interior side of the building and haven't found mold.

I'm not sure how matt_i intends to achieve "air sealing." As soon as you open a door you have broken an air seal. There's is always some amount of moisture in the air in the form of invisible vapor. An extreme cold or desert climate may have a negligible amount of moisture in the air, but you will notice the lack of moisture as you attempt to breathe.

Are you talking about the pink with fully covered fiberglass -- That's actually a good product .... but, it has holes in it. That's the only stuff I use -- it's also nice for sound .. the backing is great even agents brick.

Full plastic VB have to be installed in a way that the building will dry to the outside -- if they are in a climate or environment where humidity is present.

A typically 2x4 wall with conventional insulation will get cold in MA -- if it's humid inside ... the wall will condense.

 

[rburke65]

I’m in NE Ohio and installed the plastic VB on the bottom of my trusses, then metal ceiling panels. Also had a contractor blow glass insulation from above

 

[travisn1]

I'm torn on putting plastic against interior metal panels, any moisture that ends up against the metal (bringing in a snow covered car into a heated shop) will work it's way between the seams and just sit against the plastic, eventually rusting out the panel. I guess that's better than mold?

 

[u2slow]

Figure out what works in your climate.

Plastic, interior VB and exterior tar-paper worked fine here (pacific northwest) until the house-wrap stuff came out some 30 years ago. Then moisture/mold problems went rampant - the walls were too tight and didn't breathe.

I'm doing 6mil poly across all studs and ceiling joists before boarding. I used 60min tar-paper under the exterior steel siding.

 

[BruceMc]

You missed my point .... it's about proper insulation. You can get plenty condensation with plastic VB ... it's what caused all the problems back in the 70's and 80's when it was used. Plastic will not allow a building to dry when the condition occurs. Craft VB and all the new sheet type allow for drying .. slow moisture travel .. drying.

Not having enough insulation -- or leaks that allow moist air to travel through walls is the problem .. all made greater with plastic

If you're having moisture problems from the exterior from, say, wind driven rain, that's what you need to fix. Water vapor from the interior doesn't need an air leak to travel into the insulation. Vapor diffusion of water molecules due to differences in vapor pressure alone is enough to soak your insulation over time if you don't have a proper vapor barrier. That's what your exterior wall wrap is trying to acccomplish - allowing water vapor to flow through it while preventing air flow. Think of it as Goretex for buildings.

You can install 10 feet of insulation if you want, and you will still have problems with condensation and possible ice formation in your wall if you don't have a vapor barrier. The thickness of the insulation doesn't have anything to do with it, other than the more insualtion your have, the more water you will wind up with. A skinny sponge versus a thick sponge.

 

[Marctrees]

except if you look at the current thinking and the experience of many years -- plastic is not the way to go. Add in the new taped exterior .... Especially the zip walls -- now you have a sealed cavity .. not good.

Did anyone read this ?

https://www.iccsafe.org/wp-content/uploads/proclamations/TN06-Vapor-Retarders_pdf.pdf

Marc

 

[yeldogt]

If you're having moisture problems from the exterior from, say, wind driven rain, that's what you need to fix. Water vapor from the interior doesn't need an air leak to travel into the insulation. Vapor diffusion of water molecules due to differences in vapor pressure alone is enough to soak your insulation over time if you don't have a proper vapor barrier. That's what your exterior wall wrap is trying to acccomplish - allowing water vapor to flow through it while preventing air flow. Think of it as Goretex for buildings.

You can install 10 feet of insulation if you want, and you will still have problems with condensation and possible ice formation in your wall if you don't have a vapor barrier. The thickness of the insulation doesn't have anything to do with it, other than the more insualtion your have, the more water you will wind up with. A skinny sponge versus a thick sponge.

Then why is blown insulation done w/o VB? ... VB is needed with fiber glass ..the modern stuff not the old glass wool that was also blown into millions of homes w/o VB.

Plastic is a VB .. insulation wants a vapor retarder.

I'm not having any problems ... since I don't use plastic.

But, in a leaking building (all building leak) ... the stack effect can create negative pressure and pull outside air in .... if it's humid -- you will get humid air in your walls. The need for rain screens is a different concern

 

[yeldogt]

Did anyone read this ?

https://www.iccsafe.org/wp-content/uploads/proclamations/TN06-Vapor-Retarders_pdf.pdf

Marc

Yes and see plastic is a class 1 ... and they say only considered in the coldest climates. Because the coldest climates ... coldest ... that's cold. Have very low humidity -- and basically **** the moisture out of structures. You can have low humidity in an ice house.

The key word is retarder ...vapor retarder.

as an extra thought not related tot he OP's thread .... I think the new Zip walls are going to be a problem in the future ... just my guess

 

[Marctrees]

Why does GJ try to re invent the wheel w opinions EVERY time a VB query post come up?

Seems to me the two links I gave answer most questions if studied carefully and not mis understood.

Marc

 

[travisn1]

studied carefully and not mis understood.

This is the difficult part.

 

[Jlbc212]

Are you talking about the pink with fully covered fiberglass -- That's actually a good product .... but, it has holes in it. That's the only stuff I use -- it's also nice for sound .. the backing is great even agents brick.

Full plastic VB have to be installed in a way that the building will dry to the outside -- if they are in a climate or environment where humidity is present.

A typically 2x4 wall with conventional insulation will get cold in MA -- if it's humid inside ... the wall will condense.

I used unfaced fiberglass batts and rolls - some may have been pink or yellow. The fiberglass works by trapping air in the minute spaces between the fiber. Mice will sometimes tunnel through it. In my cold climate it is essential to use a Class I or II vapor barrier, otherwise water vapor will pass into the wall, into the insulation and condense back into liquid when it reaches the space in the wall or insulation where the temperature is at the dew point.

The only time I have seen moisture condense on an inside wall in cold MA is when there is no insulation in the 2x4 wood frame wall, the interior of the wall has a thick coating of several layers of paint and/or vinyl wall paper and something is happening inside the house causing excess amount of moisture - such as steam heat, or lots of cooking with simmering. This does happen in older structures built before energy conservation was a concern. I grew up in such a house. The older buildings without insulation and vapor barriers lasted for years and years without mold/rot because they allowed moisture to flow through the walls and ceilings to the outside without getting trapped in the walls or ceilings.

 

[yeldogt]

I used unfaced fiberglass batts and rolls - some may have been pink or yellow. The fiberglass works by trapping air in the minute spaces between the fiber. Mice will sometimes tunnel through it. In my cold climate it is essential to use a Class I or II vapor barrier, otherwise water vapor will pass into the wall, into the insulation and condense back into liquid when it reaches the space in the wall or insulation where the temperature is at the dew point.

The only time I have seen moisture condense on an inside wall in cold MA is when there is no insulation in the 2x4 wood frame wall, the interior of the wall has a thick coating of several layers of paint and/or vinyl wall paper and something is happening inside the house causing excess amount of moisture - such as steam heat, or lots of cooking with simmering. This does happen in older structures built before energy conservation was a concern. I grew up in such a house. The older buildings without insulation and vapor barriers lasted for years and years without mold/rot because they allowed moisture to flow through the walls and ceilings to the outside without getting trapped in the walls or ceilings.

Class II is fine -- you can get condensation on plastic (class 1) VB w/ 2x4 framing and simple fiberglass. My comment on the wrapped pink ..was to another poster. They fully wrapped pink is for packaging ... it's a class II w/ punched holes on the reverse.

With plastic and humidity -- the water can drips down and wet the sills ..and any horizontal framing. It not going to happen to every structure ... especially one with low humidity. but, there were many many problems years ago when the use was widespread ... TOH used it all the time. Norm made a point many years ago of pointing out the mistake

 

[yeldogt]

Why does GJ try to re invent the wheel w opinions EVERY time a VB query post come up?

Seems to me the two links I gave answer most questions if studied carefully and not mis understood.

Marc

you mentioned polly? taped polly.

If you read your link -- they don't recommend. As i said in the previous post ... coldest. That's zone 8 ... no place in the lower 48 .... even dropping down to 7 there are few spots in the USA.

 

[BruceMc]

With plastic and humidity -- the water can drips down and wet the sills ..and any horizontal framing.

Assuming you have insulation in the wall, it won't happen if the water vapor is stopped on the warm side, before it cools to the dew point and condenses out. You won't get any more condensation on the plastic than you'll get condensation on the furniture.

 

[BruceMc]

Then why is blown insulation done w/o VB?

Because the installer is either a hack or is cheating you? Or maybe you're thinking of spray foam, which doesn't need a VB?

 

[2CRUZ]

I insulated walls and ceiling in my 30x40. I used plastic on the walls and ceiling then covered with sheetrock. Now I walk out there and flip on the old Hot Dog Furnace and it is warm as toast in just a few minutes. I have a little window air conditioner and it keeps it comfortable in there on the hottest days of summer. I'm happy

 

[yeldogt]

Assuming you have insulation in the wall, it won't happen if the water vapor is stopped on the warm side, before it cools to the dew point and condenses out. You won't get any more condensation on the plastic than you'll get condensation on the furniture.

You are from a very cold climate --

I can only assume you have not seen the failures from the use of plastic VB. Dew point changes depending on temps ...

Think about what happens when you start attaching anything to the walls -- drywall .. anything .... you put holes in the plastic. all the penetrations -- switcher outlets .. anything attached to the drywall goes through the plastic.

These all become way points for leaking .....

People can do what they want obviously .. but there is a reason why it's not recommended. I don't care how many people have done it .. and maybe done it without any problems. But, the problem is real if you have the correct conditions.

It's easy to use the correct products and not have any problems

 

[yeldogt]

Because the installer is either a hack or is cheating you? Or maybe you're thinking of spray foam, which doesn't need a VB?

No --- because of moisture travel.

look up dense pack cellulose insulation -- check out the fabric sheet that is used. It's not a class 1 .. plastic is class 1.

Also -- you can't install a plastic VB when it retrofitted into an old house ... and it works great.

Why -- because it does not allow air flow that carries moisture -- and it does not trap moisture.

Fiberglass w/ plastic will -- it can be driven in from outside on a hot humid day -- and condense on the inside the plastic at the drywall when you have the AC on.

Being in a very cold climate you have very low humidity most parts of the year