Use vapor barrier when insulating unheated garage?

[Haliburton]

I'm thinking of insulating my new garage which will only be heated some of the time. I live in a cold climate (Canada). Should I put 6 ml vapor barrier between the studs and the drywall? (drywall is required to meet building code for fire protection).

Will installing a vapor barrier cause a mold problem?

 

[The Cobbler]

there's varying thoughts on vapour barrier in garages in our climate
either way will be fine IMO

 

[Haliburton]

there's varying thoughts on vapour barrier in garages in our climate
either way will be fine IMO

Thanks. I'm leaning towards not using vapor barrier to allow the garage to breathe - but am concerned this will diminish the effectiveness of the insulation. I plan on having a small heat source in there 50% of the time.

 

[pcmeiners]

Does your slab have a vapor barrier? if it does not you will have substantial vapor coming through the concrete...just another consideration.

 

[Haliburton]

Thanks PC. I was not aware of that. Maybe a good reason to have a vapour barrier.

 

[BruceMc]

I'm thinking of insulating my new garage which will only be heated some of the time. I live in a cold climate (Canada). Should I put 6 ml vapor barrier between the studs and the drywall? (drywall is required to meet building code for fire protection).

Will installing a vapor barrier cause a mold problem?

It helps prevent mold problems. The only time you wouldn't want a VB with insulation is if you plan on spray foaming, which serves as it's own VB.

 

[Haliburton]

Thanks Bruce. I've decided to go with VB. What precipitated this was that my contractor went ahead and installed insulation and drywall without putting in the VP claiming I didn't need it if the garage was unheated. I've asked him to remove the drywall now and install 6 ml PVC vapor barrier as was originally quoted and spec'd. An expensive mistake for him!

 

[matt_i]

Wow, so the drywall is "reused" now?

I would not have done that unless you have some kind of water vapor producing "thing". Like a pool, group of people inside, shower, unvented heater, etc. I suppose a propane forklift could also do it if you ran it inside a lot.

 

[Abeo]

Wow, so the drywall is "reused" now?

I would not have done that unless you have some kind of water vapor producing "thing". Like a pool, group of people inside, shower, unvented heater, etc. I suppose a propane forklift could also do it if you ran it inside a lot.

Or a car with snow and ice melting off.

 

[850xpeps]

Or a car with snow and ice melting off.

Wow, so the drywall is "reused" now?

I would not have done that unless you have some kind of water vapor producing "thing". Like a pool, group of people inside, shower, unvented heater, etc. I suppose a propane forklift could also do it if you ran it inside a lot.

Vb the garage and good choice of the op to make the contractor responsible when he quoted it.

Reused drywall? Lol screw it in different spots and patch over what’s the big deal? Much better than mold or frost in the garage when he heats it.

 

[BruceMc]

Or a car with snow and ice melting off.

Exactly.

 

[ItsNemo]

I'm up here in Canada too in the same situation, no vapor barrier here...it's just going to hold the excessive moisture from melting vehicles in even more. Plus, primed/painted drywall can in itself act as a pretty substantial vapor barrier.

 

[850xpeps]

I'm up here in Canada too in the same situation, no vapor barrier here...it's just going to hold the excessive moisture from melting vehicles in even more. Plus, primed/painted drywall can in itself act as a pretty substantial vapor barrier.

Absolutely not lol there is no point in insulating without a vapour barrier. ESP with heat. If you have heat then I suggest you pull some insulation out and look at the frost. I wouldn’t build without it an no one who knows what they are doing should.


There is code on vapour barrier required. I believe it states thickness? Common is 6mil cgsb poly. Exterior foam is aloud I think if it’s thick enough to maintain a temperature on the inside face to not cause condensation.

 

[tigeraid]

I uuuuh... Yeah this conversation is supremely weird, I've never heard of anyone NOT using vapour barrier with insulation and drywall. There's a reason it's Code. I can't imagine the mold potential without it.

If you're using rigid foam (especially with the nice foil backing) directly onto the concrete, it acts as its own barrier, mind you.

 

[ItsNemo]

Absolutely not lol there is no point in insulating without a vapour barrier. ESP with heat. If you have heat then I suggest you pull some insulation out and look at the frost. I wouldn’t build without it an no one who knows what they are doing should.


There is code on vapour barrier required. I believe it states thickness? Common is 6mil cgsb poly. Exterior foam is aloud I think if it’s thick enough to maintain a temperature on the inside face to not cause condensation.

If the garage is insulated but usually unheated, no vapor barrier...if the space is always heated, then yes vapor barrier. That's what the permits for my attached garage required here.

Garage space does not match living space from a code perspective.

 

[tigeraid]

Fair point, I wasn't thinking garage vs living space. But interior heat is definitely the key, regardless of which structure. I would imagine you wouldn't need it living in Arizona or whatever, but we're talking Canada.

 

[850xpeps]

If the garage is insulated but usually unheated, no vapor barrier...if the space is always heated, then yes vapor barrier. That's what the permits for my attached garage required here.

Garage space does not match living space from a code perspective.

He mentions heating it. Done deal. And even in an Unheated garage with insulation, a vehicle creates heat. You will create frost and mold , id lay money on it. I’ve demoed houses included one of my own I remodeled, that had frost is corners that the vapour wasn’t sealed. It was there but not sealed.

The question would be why would someone not spend the $200 to poly a garage. With the possibility of frost and mold...... the corners people cut sometimes baffle me.

If you heat it once you will have frost. So like I said why would you bother to insulate and not poly. I hope you don’t advise anyone else to not use poly.

I will try find it in my code book. But I doubt it says living space. It probably states insulated space. Code covers garages too so I would assume if insulate then vapour barrier is required by code. But I’ll try find it in my book.

 

[kbs2244]

If it is an attached garage and we are talking about the wall between the garage and the living space then no, you do not need a vapor barrier. The house side of the wall will be warmer than the garage and any vapor will stay in the garage. Outside walls will need a barrio because those wall will be cold on the outside.

The vapor will follow any heat as it travels to from warm to cold

One trick that seems wrong but works every time is to leave a door or window open a crack.
You will lose some heat, but you will have a dry garage since the vapor follows the heat.

The same trick will keep you from having frosty car windows the morning after a toasty drive melted all the snow off your show and into the car carpets.
Leave a car window open a crack.
As the wet carpet gets dry the moisture will follow the heat out the window instead on condensing on the glass and freezing.

 

[Greywarrior07]

Here’s a good video, I would rather listen to this guy who builds lots of custom homes and understands building science...

Sent from my iPhone using The Garage Journal mobile app

 

[jmlcolorado]

I saw yes. Never know when you might decide to heat down the road......AND helps a TON with wind infiltration.
I just finished framing and sheathing my pole barn with no finishes inside and I was amazed at how little wind (none noticeable) was inside while we went through a decent wind storm.

 

[madmaxnj]

Is the VB still needed if you are not dry walling? I plan to put up OSB and I don't plan it to be airtight either. Part of the reason to use OSB is so I can pop out a panel if needed to add or modify what is in the wall already. Not that I have any definite plans to change anything, but just in case. So I plan to have small gaps between all panels so I can take them in and out if needed.

Didn't mean to hijack this thread, just seemed like a good place to ask.

 

[theoldwizard1]

In cold climates, top rated builders apply VB toward the inside of the building, between the finished wall and the studs.

Some builder still use an exterior (non VB) house wrap to limit air intrusion, especially "leaky" siding (like metal).

The best method of insulation is 2" of spray foam and then 4" of fiberglass.

 

[BruceMc]

Is the VB still needed if you are not dry walling? I plan to put up OSB and I don't plan it to be airtight either.

It doesn't matter how you plan to sheath the wall, or not sheathing even. The VB is there to keep water vapor from condensing out into the insulation. In the wall of a heated building you have a thermal gradient between the inside and outside. Closed cell foam is, for all practical purposes, impermeable to water vapour and thus doesn't necessarily need a VB, but batts and loose fill insulation does.

When the temperature difference is great enough, at some point within the wall is the dew point, where the water vapour becomes liquid water. It doesn't matter if you have 2" or 20" of insulation - at some point within the wall water will condense out. When that happens, all sorts of bad things start to cascade. Once the insulation gets wet, it loses it insulation value, the dew point then moves ever closer to the inside wall, and even more moisture condenses out. In a ceiling it can load up enough that the weight of the water soaked insulation collapses the sheetrock. Over time you get mold and rot issues.

 

[Jazz1]

Yes use vapour barrier, its Canada

 

[gerryw]

Im in T.O, my 10yr old house (now 30) had the attached garage insulated plus vapour barrier. No issues whatsoever and i later (5yrs later)finished the interior walls an heated the space.

Gerry

 

[tfinniii]

I saw this 20 years ago about the air infiltration problem with moisture,they said better to seal holes and edges of wallboard.

 

[ddawg16]

In Canada, the outside relative humidity is low. Chances are, there will be more humidity in the garage....so I would put the VB on the side between the drywall and insulation.

 

[TractorJeff]

What about the Insulation that has Kraft paper on it? Isn't that considered a Vapor Barrier? If you buy a Garage Kit from a Box Store they don't include Vapor Barrier. Do they assume that the Kraft paper is the Vapor Barrier?

 

[850xpeps]

In Canada, the outside relative humidity is low. Chances are, there will be more humidity in the garage....so I would put the VB on the side between the drywall and insulation.

It isn’t about where you are. The insulation must be min on the warm side of the insulation. No more than 1/3 insulation inside the vapour barrier.

 

[BruceMc]

What about the Insulation that has Kraft paper on it? Isn't that considered a Vapor Barrier? If you buy a Garage Kit from a Box Store they don't include Vapor Barrier. Do they assume that the Kraft paper is the Vapor Barrier?

You'll find it touted as such, and it is better than nothing, but not by very much. Visqueeen is both cheap and far easier to instal properly than Kraft-faced insulation.

 

[850xpeps]

You'll find it touted as such, and it is better than nothing, but not by very much. Visqueeen is both cheap and far easier to instal properly than Kraft-faced insulation.

That kraft faced insulation has no place in walls that actually need insulation. Some people seem to think of something claims it can do something they are ok with that. Even though it does it poorly or not at all. Doing something half way in building is almost always worse than not doing it at all.

 

[BruceMc]

That kraft faced insulation has no place in walls that actually need insulation. Some people seem to think of something claims it can do something they are ok with that. Even though it does it poorly or not at all. Doing something half way in building is almost always worse than not doing it at all.

About the only place it's useful is in overhead installations, where stapling it to the rafters helps keep it from falling out. At least until you can come back and install the visqueen and sheathing.

 

[850xpeps]

About the only place it's useful is in overhead installations, where stapling it to the rafters helps keep it from falling out. At least until you can come back and install the visqueen and sheathing.

I don’t think it does a proper job of filling spaces. Personally I would poly and strap then blow in or poly and sheet and blow in after.

 

[yeldogt]

The use of plastic VB should be avoided in almost every case .... the key to good buildings is to air seal. The movement of air is the main driver of moister into a wall ... with no air path the water movement is so low that anything will dry.

Plastic VB will trap moisture -- very bad. Just because you see something all the time .. does not make it correct. I'm always making comments about not venting .. it's the same thing/idea ... we have been doing things now for a couple generations. But, it's not based on sound science ... it's .. well we always did it that way.

do a google search -- and see those homes with early mold and wall failures ... plastic is the problem. In humid areas -- it's the wall ... in dryer areas it's the backside of the drywall.

Batt type insulations -- even Roxul will allow air movement. If you install plastic -- you run the risk of trapping that moisture. Paper VB retards air movement -- and moisture movement but it does not stop moisture movement .. so the wall can still dry to both the inside and outside.

Plastic .... should be used under a slab .. that's about it.

 

[850xpeps]

The use of plastic VB should be avoided in almost every case .... the key to good buildings is to air seal. The movement of air is the main driver of moister into a wall ... with no air path the water movement is so low that anything will dry.

Plastic VB will trap moisture -- very bad. Just because you see something all the time .. does not make it correct. I'm always making comments about not venting .. it's the same thing/idea ... we have been doing things now for a couple generations. But, it's not based on sound science ... it's .. well we always did it that way.

do a google search -- and see those homes with early mold and wall failures ... plastic is the problem. In humid areas -- it's the wall ... in dryer areas it's the backside of the drywall.

Batt type insulations -- even Roxul will allow air movement. If you install plastic -- you run the risk of trapping that moisture. Paper VB retards air movement -- and moisture movement but it does not stop moisture movement .. so the wall can still dry to both the inside and outside.

Plastic .... should be used under a slab .. that's about it.

Completely wrong. There is a reason it is code. The poly does not trap moisture when there is no vapour barrier on the outside of the wall. Your theory is crazy. Why would Vb produce mold? When you seal a house you also need to install a proper hrv system to replace the inside air with fresh air. A hrv is also code and must be installed on new houses.

Your first sentence baffles me. You say plastic vb should be avoided and then follow it by you must stop air movement....which is what the poly does. I don’t even know why I would reply to your post but it seems like you don’t know how good building practices are. You vent on the outside to keep the air flow and avoid moisture build up and you seal inside to keep the warm air from condensing and causing moisture inside a wall. I hope you are not a builder and are advising people the way you seem to think stuff should be built.


Sent from my iPad using Tapatalk Pro

 

[tng2000]

You absolutely need to use vapour barrier. I'm just in Richmond hill and just finished tearing out all the drywall the previous owner installed. the garage was very damp in the winter from melting snow, and the drywall was sagging from the moisture it absorbed. The garage was fully insulated with fiberglass insulation some of which I had to replace because of black mold, further, the garage roof was leaking in two places which made things even worse !. I'm just in process of putting in vapour barrier now and will start installing new drywall in about a week.

 

[yeldogt]

Completely wrong. There is a reason it is code. The poly does not trap moisture when there is no vapour barrier on the outside of the wall. Your theory is crazy. Why would Vb produce mold? When you seal a house you also need to install a proper hrv system to replace the inside air with fresh air. A hrv is also code and must be installed on new houses.

Your first sentence baffles me. You say plastic vb should be avoided and then follow it by you must stop air movement....which is what the poly does. I don’t even know why I would reply to your post but it seems like you don’t know how good building practices are. You vent on the outside to keep the air flow and avoid moisture build up and you seal inside to keep the warm air from condensing and causing moisture inside a wall. I hope you are not a builder and are advising people the way you seem to think stuff should be built.


Sent from my iPad using Tapatalk Pro

I know what i speak .. do some research before you say someone is wrong.

It's not hard to find the facts. Mold has become a problem because people keep using impermeable barriers.

The whole reason for the development of house wrap was to solve the air intrusion problem and still be able to use inexpensive fiberglass batts.

venting and plastic are bad bad bad ... Have not done either in over 30 years. Foam is the best with proper positive fresh air intake .. but a good building can be done with batts ... not with plastic.

There are many recent studies ... it's not new. When polly first started to be widely used after the energy crunch in the early 70's -- it did not take long before the problems become noticeable. The tighter the building the bigger the problem. saw many in the 80's when I started.


follow the link in an earlier post ... explains part of it and discusses where to get more information

 

[yeldogt]

You absolutely need to use vapour barrier. I'm just in Richmond hill and just finished tearing out all the drywall the previous owner installed. the garage was very damp in the winter from melting snow, and the drywall was sagging from the moisture it absorbed. The garage was fully insulated with fiberglass insulation some of which I had to replace because of black mold, further, the garage roof was leaking in two places which made things even worse !. I'm just in process of putting in vapour barrier now and will start installing new drywall in about a week.

exterior water intrusion will add huge amounts of moisture -- w/o air movement the amount of water that get transferred through drywall in a garage is minimal .. A structure will dry from both sides .. that's why house wrap was developed.

A leaking roof would cause even more issues with plastic VB.

Do a google search on the subject -- there have ben recent studies.

 

[850xpeps]

I know what i speak .. do some research before you say someone is wrong.



It's not hard to find the facts. Mold has become a problem because people keep using impermeable barriers.



The whole reason for the development of house wrap was to sold the air problem and still be able to use inexpensive fiberglass batts.



venting and plastic are bad bad bad ... Have not done either in over 30 years. Foam is the best with proper positive fresh air intake .. but a good building can be done with batts ... not with plastic.

Keep doing what your doing then. I’ll build properly with a vapour barrier on the warm side of insulation, moisture barrier on outside, proper home air system and proper venting. All which are code and imo and understanding of moisture, and condensation and fresh air and proper building envelope, the proper way to build. My way keeps no mold or water issues and a properly insulated and efficient built house.

Spray foam traps moisture.

 

[850xpeps]

exterior water intrusion will add huge amounts of moisture -- w/o air movement the amount of water that get transferred through drywall in a garage is minimal .. A structure will dry from both sides .. that's why house wrap was developed.



A leaking roof would cause even more issues with plastic VB.



Do a google search on the subject -- there have ben recent studies.

No vapour barrier isn’t a good reason because of a leaky roof. Wtf a non leaking roof and proper ventilation and moisture barrier on the exterior let the wall breathe. So what are you talking about? Poly on the warm side does not trap water in a wall? It can escape through the outside with a properly constructed house.