Vapor barrier in garage ceiling

Cougar · Apr 2, 2011

Want to finish the attached garage.
When the house was built they rocked the firewall and ceiling in the garage.
But they didn't put a vapor barrier in the ceiling.
Want to insulate everything, what's the best way to install a vapor barrier in the ceiling after it's been rocked.
Thanks

rickairmedic · Apr 2, 2011

Take the sheetrock down put up the vapor barrier then put new sheetrock up . I will ask are you planning to heat the garage if so I wouldnt worry so much about a vapor barrier .

Rick

Berserker · Apr 2, 2011

even if you are heating the garage, is it a big deal not to have one? My house was built in 1973, I don't have a vapor barrier in the house. I bought nsulation with a vapor barrier for the garage though.

I would make sure the garage is vented good, and move on with your life.

Berserker · Apr 2, 2011

I think they may paint that is a vapor barrier.

rickairmedic · Apr 2, 2011

My house was built in 65 they didnt even know what insulation was then much less vapor barrier . I have installed kraft backed batts as I have worked on the house removing and replacing drywall.

Rick

venom50svt · Apr 2, 2011

This thread prompts me to ask.... I you build or reside your garage or house and you use Tyvek on the outside of the structure is that a vapor barrier or is it just for air infiltration......
I know when I put insulation in with kraft paper I staple the flanges to the studs and the room looks like a giant paper bag... If that is a so-called vapor barrier how does that interact with the outside tyvek....

LIVELY · Apr 2, 2011

TYVEK IS BOTH---it does breath if installed properly

kb2tha · Apr 2, 2011

My understanding is that Tyvek is an infiltration barrier but not a vapor barrier. If it was a vapor barrier; putting it on the outside (cold side as designed) would trap moisture in your walls and eventually do serious damage.

As long as you have adequate ventilation above your ceiling you should be good to go. You will likely find a 50/50 mix of opinions on this topic. Walls, yes. Ceilings, no (with proper ventilation).

Just finished the final barrier on my walls in my garage. Used some 6 mil poly left from when the concrete was poured and covered.
Ken

kbs2244 · Apr 2, 2011

Over and over again.

Vapor barrier vs. moisture barrier.

Tyvek is a MOISTURE barrier.
Moisture is LIQUID water.
Tyvek is, by design, vapor permeable.
That means it will let vapor through.
Its purpose is to keep any rain (liquid) that gets through the siding from getting into the wall.
It is also used as a wind barrier.

Vapor is water as a gas.
We call it humidity.
Poly and well sealed Kraft (nobody does it correctly) are vapor barriers.

Water vapor will, by its nature, go to cold.
As far as it can, before condensing.

You want a vapor barrier on the warm side of the wall to keep any humidity generated inside from getting into the wall in the first place.
But if some gets into the wall, you want it to pass through the insulation, AND the moisture barrier, to the outside siding. There it will condense and drain down the inside surface of the siding and out the drain holes that should have been part of the siding job.

Even brick sided wall will have “weep holes” in the bottom row of bricks.

This is why the south side of a wood sided house will have problems with the paint peeling.
The sun will keep the siding warm enough so the vapor will not condense.
But nobody ever vents the top of a siding job. So the vapor cannot escape and goes through the siding, popping the paint off in the process.

A roof, especially a black one, is an extreme case of the south wall problem.
Keep as much vapor out of it as you can.
But allow lots of venting above the insulation, both IN as well as out, for the vapor that does get through.

brownbagg · Apr 2, 2011

you dont want vapor barrier on ceiling, moisture rise and collect on the plastic, rotting out the sheetrock. Just let it pass, not hurting anything

Cougar · Apr 2, 2011

Thanks for the replies.
Yes, no, maybe. That narrows it down.

It will be a bit before I get to it. When I do maybe I'll put on a couple coats of the vapor barrier primer paint and be done with it.
It is vented good with a continuous ridge and soffit vents.
May heat occasionally.

e-tek · Apr 2, 2011

rickairmedic said:
Take the sheetrock down put up the vapor barrier then put new sheetrock up . I will ask are you planning to heat the garage if so I wouldnt worry so much about a vapor barrier .

Rick

Wouldn't it be even MORE important if you where going to heat the garage? That would cause a ton of moisture from the cars steaming/melting/rain water evaporating.... I'd vapour barrier and have an exhaust fan (as I do now).

brownbagg said:
you dont want vapor barrier on ceiling, moisture rise and collect on the plastic, rotting out the sheetrock. Just let it pass, not hurting anything

\

WHAT???? :wtf:

You put VB to stop the moisture from contacting the insulation. Wet insulation = MOLD.

rickairmedic · Apr 2, 2011

E tec how did you get all that stuff on the cars in your garage . I thought yours was like mine storage for the toys and workshop . There shouldnt be any of that stuff on the cars in there

.

Rick

rburke65 · Apr 2, 2011

kbs2244...well, do we put a VB on the ceilings? You sound knowledgeable...

Berserker · Apr 2, 2011

My house has no vapor barrier, and I do heat it.

mrpaco69 · Apr 2, 2011

if there is no living spaces above the garage (bedroom ,living room)remove the drywall,insulate the ceiling,use 6mil poly for vapor barrier,drywall with 5/8 alot of building codes call for 5/8 drywall in a garage on ceilings and wall abutting living spaces.hope it helps.or just call your building dept and ask one of thir inspectors most are helpful then again there is always the one **** head there. lol

Racecarl · Apr 2, 2011

My 24 X 30 has 2 X 6 sidewalls, so I put R-19 unfaced fiberglass in the walls. I then put on 10 mil clear plastic and then 1/2" OSB for interior wall sheathing. For the ceiling I stapled up the 10 mil plastic, and then sheathed the ceiling with OSB. This afternoon we blew in around 16" of cellulose, so now my garage is fully insulated.

While I was installing the sheathing on the walls, it was pretty cold and windy. The plastic vapor barrier made a lot of difference. I have the outside walls covered with houswrap and have just begun installing the siding.

trbomax · Apr 2, 2011

mrpaco69 said:
if there is no living spaces above the garage (bedroom ,living room)remove the drywall,insulate the ceiling,use 6mil poly for vapor barrier,drywall with 5/8 alot of building codes call for 5/8 drywall in a garage on ceilings and wall abutting living spaces.hope it helps.or just call your building dept and ask one of thir inspectors most are helpful then again there is always the one **** head there. lol

I dont think I would do that unless you plan on permitting the job. You may open a can of worms that would be best left closed, not saying you shouldnt permit it,or that you should,just ,well, you can use your imagination.

e-tek · Apr 2, 2011

Berserker said:
My house has no vapor barrier, and I do heat it.

But that doesnt make it right.... Our undertanding of building envelope technology has come a llllooong way in 20 years.>>>>>

While I was installing the sheathing on the walls, it was pretty cold and windy. The plastic vapor barrier made a lot of difference. I have the outside walls covered with houswrap and have just begun installing the siding.

EXACTLY. Another good reason for VB - it's a systems approach.

e-tek · Apr 2, 2011

rickairmedic said:
E tec how did you get all that stuff on the cars in your garage . I thought yours was like mine storage for the toys and workshop . There shouldnt be any of that stuff on the cars in there .

Rick

You mean rust? :headscrat

rickairmedic · Apr 2, 2011

e-tek said:
You mean rust?

LOL no I meant water and stuff .

That would mean something had to go outside in bad weather

.

Rick

kbs2244 · Apr 3, 2011

So, do you put a VB on the ceiling?
I say no if all you have above is an attic.

Just vent above the ceiling well.
Any vapor that goes through will stay vapor until it goes out the vent.
That is how they do it in home construction.

I have seen frost in an attic.
But you always find a bathroom or dryer vent dumping up there.
That over loads the vents.

Vaulted ceilings are a different story.
My next build will be a finished, and insulated, vaulted ceiling shop with a black metal roof.
Vented furnace, but sometime wet work being done.

I am still researching how it should be done.
Right now it looks like 2x6 rafters, with 4 inches of insulation, leaving a 2 inch air gap that gets vented at the eve and ridge.

I don’t know about a ceiling VB.
I am leaning towards one to keep any humidity out of the small air gap and then using a humidistat controlled room vent at the ridge.

dirttracker18 · Apr 3, 2011

brownbagg said:
you dont want vapor barrier on ceiling, moisture rise and collect on the plastic, rotting out the sheetrock. Just let it pass, not hurting anything

Soooo wrong for so many reasons

OP You are in the same climate as I am. If you consult with the insulation companies in your area you will find that you need vapour barrier on the warm side of all walls and ceiling. It will not collect and rot the dry wall.

I am thinking those that are not using it are in the southern US or are just uninformed.

Vapour barrier acts as more than just a barrier to moiture (water in air "vapour" is still moisture).

Batt insulation does not stop the movement of air, only attempts to control the movement of temperature. The vapour barrier becomes the seal to stop air moving from inside to outside when heated or outside heat in the summer to the inside.

If you heat your garage in your climate without a vapour barrier you will lose a lot of warm air out your ceiling. Try holding up a batt and blowing a fan at it, you will feel the air move right through it.

You can have the attic space spray foamed with a closed cell foam instead of taking the drywall down. The closed cell foam will be both your insulator and vapour barrier in one. It is usually about 30% more then batts but figure in the cost to replace you drywall and see what makes sense for you.

Others will debate the vapour barrier issue here but your local insulation companies will confirm what I told you here

All that being said, if you do not intend on heating the shop then this is a moot point. Just leave it as is for now.

dlenkewich · Apr 3, 2011

e-tek said:
But that doesnt make it right.... Our undertanding of building envelope technology has come a llllooong way in 20 years.>>>>>

EXACTLY. Another good reason for VB - it's a systems approach.

E-tek, building codes differ wildy, specially through-out the US. So their system is most likely much different, and likely a lot less stringent then ours. Living in a climate like ours (With hot summers and extremely cold winters), we've got requirements here that are more stringent and complicated then most of Canada. Even hope over to alberta, the materials are the same, but the general process of sealing and caulking is different. (Some say that's why there are so many mold remidiation companies there vs. here.)

And it's easy to forget that the process of insulating (anywhere in north america) was way different pre-1980's/90's versus now. Homes done with lathe and plaster usually did not have an official vapour barrier, but most believed the plaster did make up for it a great deal. Where as now our standard sheet-rock and mud is much less 'hardy' a system then lathe and paster.

Cougar · Apr 3, 2011

Keep em coming.
Now I'm leaning towards taking the drywall down and redo the whole works.

e-tek · Apr 3, 2011

rickairmedic said:
LOL no I meant water and stuff . That would mean something had to go outside in bad weather .

Rick

Sorry Rick, I was talking about my 2-car attached earlier. In that one the daily drivers are brought in and melt/dry off creating a lot of mositure. I put a big box fan in the window and run it 24/7/365 to keep the mositure from building up in there.

My shop is like yours - storage and workshop. I don't even work on the wet/snowing Daiy lDriver's in there!

PCO6 · Apr 3, 2011

I put up a vapour barrier. I have an aluminum ceiling and a well vented attic above. The barrier keeps the heat in and there's no evidence of moisture.

And for Rick above, my house was also built in the mid 60's. Other than in the attic, there are no signs of insulation here either. Heat was cheap back then.

Cougar · Apr 3, 2011

PCO6 said:
I put up a vapour barrier. I have an aluminum ceiling and a well vented attic above. The barrier keeps the heat in and there's no evidence of moisture.

And for Rick above, my house was also built in the mid 60's. Other than in the attic, there are no signs of insulation here either. Heat was cheap back then.

That looks nice, is that aluminum soffit.

e-tek · Apr 3, 2011

dlenkewich said:
E-tek, building codes differ wildy, specially through-out the US. So their system is most likely much different, and likely a lot less stringent then ours. Living in a climate like ours (With hot summers and extremely cold winters), we've got requirements here that are more stringent and complicated then most of Canada. Even hope over to alberta, the materials are the same, but the general process of sealing and caulking is different. (Some say that's why there are so many mold remidiation companies there vs. here.)

I hear ya, but there are still generally accepted building practices to make a building act like a complete system. Whether they are doing it or not is a different story. If the OP (who is in Wisconsin I beleive), wants to do it right, he should have a VB on the warm side, so as to avoid any moisture going though the wall and soaking the insulation, making it ineffective and creating mold. The only places in NA (geographically) you don't use a VB - or move it to the outside of the wall - is in the SOUTHERN-most US sates.

Quote:
The idea behind the vapor barrier is to keep moisture that develops inside the house inside. Without the barrier, here is what happens inside the wall in winter: Warm, moist air moves through the drywall and into the insulated wall cavity; at some point inside the cavity it becomes cold enough for the moisture to condense, soaking the insulation. The vapor barrier prevents this process. In older homes, the siding and sheathing were so loose that air easily migrated out before the moisture condensed, but that is no longer the case so the barrier is essential.

And it's easy to forget that the process of insulating (anywhere in north america) was way different pre-1980's/90's versus now. Homes done with lathe and plaster usually did not have an official vapour barrier, but most believed the plaster did make up for it a great deal. Where as now our standard sheet-rock and mud is much less 'hardy' a system then lathe and paster.

As per above, just the opposite is true. Older homes where built so "loose" that they allowed a ton of airflow through the walls. This allowed any moisture to go through negating the need for a VB - BUT, it also let heat out (winter), or in (summer).

Today, the standard is the following (from inside to out): Paint, Drywall, Vapour barrier (caulked and taped), insulation, OSB, Tyvek, siding. Period. In the Southern-most states it's the same, but they move the VB to the outside wall to stop heat/moisture from coming IN and soaking the insulation (Only in a very small geo. area they may not use any VB).

This gives you a sperate building envelope where you can control the environment independant of what's occuring outside. BUT, you have to CONTROL it - with air makeups, fans, heating systems, AC and dehimidifiers, depending on your location.

Berserker · Apr 3, 2011

Cougar said:
Keep em coming.
Now I'm leaning towards taking the drywall down and redo the whole works.

I am not about to tear all the drywall down in my house. I live in WI, hot summers and cold winters. From UP, lots of houses without vapor barriers.

I am not saying they are not good. I went through and added quite a bit of insulation to my house this winter. Everything looked good. I will check on it in the future to make sure the added insulation didn't cause a problem.

I would look at some kind of paint, before tearing down the drywall.

dlenkewich · Apr 3, 2011

Period? Not likely. Just from being a memeber on here, you knotice how many different ways people approach their insulation system. I was very much suprised to see how many regions still used kraft back, homes around these parts haven't used kraft back in decades, just goes to show the varying methods used.

And those older homes generally have a lot less problems overtime then the new ones do. Despite being less efficient, they've stood the test of time (Usually a bigger issue is the foundation underneath them keeping up). New homes are so sealed up that they have a lot more issues with moisture traps.

There are people who will spend every dime they have on a project like this making sure its done perfect, no one's saying their wrong. But when the project is a garage on a house built 4 decades ago, you're wasting a lot of money considering the rest of the home is still back in 1970.

Given the location, should a vapour barrier be used? Sure. Is the house going to fall apart without it? Nope. To say that it will mold if not done without a vapour barrier is wrong, many houses all over North America don't have a sufficient vapour barrier, and while some may have issues, a lot do not.

e-tek · Apr 3, 2011

dlenkewich said:
Period? Not likely. Just from being a memeber on here, you knotice how many different ways people approach their insulation system. I was very much suprised to see how many regions still used kraft back, homes around these parts haven't used kraft back in decades, just goes to show the varying methods used.

And those older homes generally have a lot less problems overtime then the new ones do. Despite being less efficient, they've stood the test of time (Usually a bigger issue is the foundation underneath them keeping up). New homes are so sealed up that they have a lot more issues with moisture traps.

There are people who will spend every dime they have on a project like this making sure its done perfect, no one's saying their wrong. But when the project is a garage on a house built 4 decades ago, you're wasting a lot of money considering the rest of the home is still back in 1970.

Given the location, should a vapour barrier be used? Sure. Is the house going to fall apart without it? Nope. To say that it will mold if not done without a vapour barrier is wrong, many houses all over North America don't have a sufficient vapour barrier, and while some may have issues, a lot do not.

Point taken. I shouldn't have used the term "PERIOD". Period. :thumbup:

But again, the reason the older homes don't have problems is because of the amount of air movement through the walls, windows, roof, etc. Now-a-day builders are trying to seal the home for energy efficiency, which does make it difficult to deal with properly. e.g. Does an OLD home need a fan in the bathroom? Maybe not. Does a new one? Most likely!

I'm pretty sure (from research and experience) that my garage VB is helping with my heating bill. It limits air and therefore heat escape.

dlenkewich · Apr 3, 2011

e-tek said:
Point taken. I shouldn't have used the term "PERIOD". Period.

But again, the reason the older homes don't have problems is becuase of the amount of air movement through the walls, windows, roof, etc. Now-a-day builders are trying to seal the home for energy efficiency, which does make it difficult to deal with properly. e.g. Does an OLD home need a fan in the bathroom? Maybe not. Does a new one? Most likely!

I'm pretty sure (from research and expereince) that my garage VB is helping with my heating bill. It limits air and therefore heat escape.

Your right on, new homes need so much interms of mechanical to keep the air inside the home balanced, it's crazy. Like I said, old homes aren't efficient, but damn, as far as a good lasting home, they built them well back in those days. Not to mention the craftmanship and character that is in old homes blows new homes away.

Your vapour barrier is definatley helping the energy bills. Insulation itself slows the tranfer of warm and cold air, and your right-on, a vapour barrier, caulked taped and sealed will stop it. From there, on a wall, you loose energy out your windows and doors.

PCO6 · Apr 3, 2011

Cougar said:
That looks nice, is that aluminum soffit.

Yes. I got it at Home Depot. It was very easy to install by myself - light weight, no taping, painting, etc. It's simply screwed to the strapping. I also like it because it reflects the light well.

HemiEd · Feb 25, 2013

New here, and thought it might be best to post my question in an existing thread. I am sure some of you vets get tired of the same old questions, but my situation seems unique to a lot of the search results I am finding.

Hopefully you all don't mind me bothering you with this question, as I am confused.

We just had a 32x36 garage added with a second floor (bedrooms etc.) above it.
The ceiling in the garage, and the walls are not rocked yet, but have the batting in them.

In a couple weeks I was planning on sheetrocking the ceiling and walls.

Eventually, I will heat the garage, but not now. (it is in Southern Missouri on Table Rock lake)

The batting in the (garage ceiling/upstairs floor) has the vapor barrier down towards the garage. Should I flip it around, or add the 4 mil plastic prior to putting the drywall up?

The side walls have tyvek on the outside of course, and I plan on putting the 4 mil plastic up prior to the sheet rock. Is that correct?

thoughts?

Thank you for any help in advance!
Ed

brachus12 · Feb 25, 2013

kbs2244 said:
You want a vapor barrier on the warm side of the wall to keep any humidity generated inside from getting into the wall in the first place.

What about buildings in Southern climates? For most of the year the outside of the building is the warm side of the wall.

kbs2244 · Feb 25, 2013

The basic rule is you want the VB on the warm side to prevent water vapor getting into the wall and then condensing in the wall.

In your case, I doubt the garage ceiling will get that cool.
You will be keeping the bed rooms warmer than the garage.
Your insulation there is more to keep the bedroom floors warm.
A VB is a not needed, but will not hurt.

Depending on how cold it gets in your area, you may or may not, need a VB in the walls.
Do you wash cars in there when it is below freezing outside?

HemiEd · Feb 25, 2013

HemiEd said:
New here, and thought it might be best to post my question in an existing thread. I am sure some of you vets get tired of the same old questions, but my situation seems unique to a lot of the search results I am finding.

Hopefully you all don't mind me bothering you with this question, as I am confused.

We just had a 32x36 garage added with a second floor (bedrooms etc.) above it.
The ceiling in the garage, and the walls are not rocked yet, but have the batting in them.

In a couple weeks I was planning on sheetrocking the ceiling and walls.

Eventually, I will heat the garage, but not now. (it is in Southern Missouri on Table Rock lake)

The batting in the (garage ceiling/upstairs floor) has the vapor barrier down towards the garage. Should I flip it around, or add the 4 mil plastic prior to putting the drywall up?

The side walls have tyvek on the outside of course, and I plan on putting the 4 mil plastic up prior to the sheet rock. Is that correct?

thoughts?

Thank you for any help in advance!
Ed

Well, I did dig out my builder invoice and found out that he used Advantech 3/4 inch t/g sub floor, so that should be sufficient for a vapor barrier.

Now, trying to learn whether I should peel the paper off of the batting that is currently in place, or flip it around prior to installing the sheetrock on the ceiling.

HemiEd · Feb 25, 2013

kbs2244 said:
The basic rule is you want the VB on the warm side to prevent water vapor getting into the wall and then condensing in the wall.

In your case, I doubt the garage ceiling will get that cool.
You will be keeping the bed rooms warmer than the garage.
Your insulation there is more to keep the bedroom floors warm.
A VB is a not needed, but will not hurt.

Depending on how cold it gets in your area, you may or may not, need a VB in the walls.
Do you wash cars in there when it is below freezing outside?

Thanks very much for your response kbs2244.

I don't plan on washing any cars in there, but it is pretty humid around the lake as you might suspect during the summer. I am just trying to due my best due diligence without introducing new problems.

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