Vapor barrier needed in Michigan?

[Ross/Kzoo]

I just built a detached garage 28 x 32 with 2 x 6 10' sidewalls. It has OSB and cement board lap siding. I plan on 1 x 3 horizontal strapping and vertical white metal walls. It will only be heated when I'm in the workshop area. My question is if a vapor barrier is needed or will I be trapping moisture between the steel walls and the insulation?

 

[BlackTalon]

The vapor retarder goes on the warm side (i.e., interior) side of the insulation. The purpose is to prevent moisture from the warmer garage interior from entering the insulation where it will then condense on the cold metal siding.

 

[kbs2244]

Yes, you will need a VB.
And BlackTalon is correct that it goes on the warm side.

If you are using metal siding as the interior wall surface the VB will go between the siding and the insulation.
Then the siding will be on the warm side.

Depending on how much vapor you create, and how well you seal the siding panels, the siding may actually act as a VB before the vapor gets behind it.
That would make the poly redundant.
But for the price of the poly, I don’t think the gamble is worth the chance.

 

[BlackTalon]

Thanks for the correction! The metal siding is on the interior not exterior. The condensation would form on the sheathing.

 

[kbs2244]

This is the kind of building the codes do not cover.

If you install the inside steel siding in large sheets (4x8 or 4x10) and caulk at the edges for sealing, then I can see the lack of a need for a poly VB.

But; just keep the overall concept in mind.

You do not want water vapor to get into the insulation area of the wall.
That is where it will change from vapor to moisture and cause the problem.

Keep in mind any top and bottom sealing needs.
Water vapor will follow any heat leak to it’s end to be equal.
So having weather tight walls, may not be what you after cooking for.

 

[plott hound]

The vapor retarder goes on the warm side (i.e., interior) side of the insulation. The purpose is to prevent moisture from the warmer garage interior from entering the insulation where it will then condense on the cold metal siding.

yupper^^^^^

 

[JCByrd24]

The metal siding is on the inside guys! Also, OSB on the outside is fairly resistant to vapor as well, thus the OPs concern of trapping moisture is legit if he puts up a poly vapor barrier. The problem will not be in the winter in a garage that is rarely heated and there is likely very little moisture to speak of except for occasional snow melt etc. It will be in the summer on a hot humid day after rain when the fiber cement and OSB is wet and being pounded by the sun driving vapor inwards. Poly would trap this and the wall would be wet all summer and then will likely not dry in the winter either. The OP wants a vapor retarder at most, and honestly I'm not sure what to recommend here, as implementation will be tricky (drywall with paint is the norm and is pretty easy). The type of insulation would make a big difference. If foam or dense pack cellulose I'd do nothing. If batts you need to air seal the bays to maintain the effectiveness of the insulation. In that case Tyvek would work well with the details done right (the same details that poly would need to do right).

Vapor barrier on the warm side is no longer the rule; vapor retarder (drywall with paint) is sufficient most of the time and not nearly as risky.

 

[BlackTalon]

What is 'rarely heated'? OP says "it will only be heated when I'm in the workshop area", but is that daily? weekly? (the metal siding on the inside ws already clarified above)

How hot and humid is it up there in the summer? My sister is in the UP, and they definitely do not have a long period of hot weather.

So lots of variables here, and arguements each way. I think more info on how often it will be heated would be worthwhile. Also it's a 'vapor retarder' and not a 'vapor barrier', as there is capacity for the VR to breathe.

OP, try this. Go to henry.com and find contact info for the tech department. Call them and describe your construction, etc. and get some basic recommendations from them. They have a good mix of air barriers and vapor retarders, and are well-versed in the wall cross-section dynamics. And they originated up in Canada, so they definitely have knowledge about the conditions up north.

 

[mygarageone]

For one thing , he needs a VB no matter what . Second thing is there 's not enough additional expense to even talk about. 3rd thing , occasionally can change to a lot more .

Why take the chance ? Geez what does plastic wrap cost. $40.00 & some time.

Just do it and know your covered .

Every time he heats that garage , there will be moisture build up in side that wall !

 

[kelpaso1]

For one thing , he needs a VB no matter what . Second thing is there 's not enough additional expense to even talk about. 3rd thing , occasionally can change to a lot more .

Why take the chance ? Geez what does plastic wrap cost. $40.00 & some time.

Just do it and know your covered .

Every time he heats that garage , there will be moisture build up in side that wall !

I agree.

 

[JCByrd24]

The problem is you guys are wrong and plastic wrap can cause problems. Just google it, there is almost no instance where building scientists recommend vapor barriers (plastic wrap) on the interior now. The ones that do are usually cold climates with very high interior humidity like indoor swimming pools.

He needs a vapor retarder and well seals air barrier but a vapor barrier will actually cause problems with OSB as the sheathing because neither breathe that well. If he had board or fiberboard sheathing it wouldn't be as risky.

Also, unless he is heating with an unvented propane heater, where do you think the moisture is coming from when he heats is garage. The relative humidity in a garage will be very low in the cold season in MI.

Also, it doesn't matter how short the summer season is, if moisture is driven into a cavity that can't dry for a couple months it will remain wet.

Here is a good link to read, with another one linked inside:
http://www.energyvanguard.com/blog-...54110/You-Don-t-Need-a-Vapor-Barrier-Probably

 

[BlackTalon]

The problem is the term 'vapor barrier' is being used by some instead of 'vapor retarder'. Also, be careful of getting reliable info by Googling, as you get a lot of stuff written by people who have no idea what they are talking about.

 

[d3ad1ysp0rk]

I'm in Maine, similar climate and usage patterns, just with drywall instead of a metal interior. I found no one can agree when it comes to this situation. I'm going without.

 

[CNGsaves]

OP . . . . did you put housewrap or tar paper on the OSB exterior before you put on the cement-board exterior siding??

 

[p1capt]

Not a scientist or engineer but I have been around the building trades for 30 years. Vapor barriers are tried and true and have worked for longer than I've been around. I would go with tried and true. Just my opinion.

 

[Rockcam]

I agree with JC here - a poly vapor barrier on the inside and painted cement board exterior may result in a "diaper" as the energy nerds call it, potentially trapping moisture where the insulation lives.

This is newer thinking from people doing long term research, like green building advisor and building science corporation.

You might want to read up on their white papers before you go down the wrong road.

 

[Ross/Kzoo]

OP . . . . did you put housewrap or tar paper on the OSB exterior before you put on the cement-board exterior siding??

Yes, there is house wrap.

Thanks for the link JC. I'm leaning this way to seal the joints since there will be no other intrusion of air and I will have steel interior walls. If I seal the joints and have the house wrap on the outside any other moisture should be inconsequential.

 

[CNGsaves]

With housewrap on outside, there should not be any moisture getting to the insulation, as that's whole purpose of housewrap (let insulation breathe out, but not allow water in).

OP is in Michigan which definitely is cold zone. I'd follow local practice and use vapor barrier on warm side. Thus, insulate your walls then cover with VB and air seal outlets or other potential air leaks into building. Since OP is not putting up sheetrock with taped joints (instead steel interior covering), he won't have "envelope" to keep warm air inside the garage, thus making good air/vapor barrier all that more important.

 

[rancherbill]

I just built a detached garage 28 x 32 with 2 x 6 10' sidewalls. It has OSB and cement board lap siding. I plan on 1 x 3 horizontal strapping and vertical white metal walls. It will only be heated when I'm in the workshop area. My question is if a vapor barrier is needed or will I be trapping moisture between the steel walls and the insulation?

The 'vapor barrier' is really two things. It is a vapor barrier and an air barrier. It is necessary. On the outside you need something like Tyvek. It is a moisture barrier that restricts moisture going into the wall and permits moisture in the walls to escape.

 

[JCByrd24]

You need and air barrier absolutely, not arguing that, this is an area all the building scientists have figured out. Air sealing is much more important than blocking vapor. This is the hard part about what the OP is trying to do. Vapor diffusion through a solid sheet of painted sheet rock is very very little. So much so that you don't need a separate vapor barrier most of the time. However vapor will quickly travel and condense through air leaks.

Blacktalon, these boys are talking about plastic/poly, that is a class 1 vapor retarder, AKA a vapor barrier.

Also, Typar/Tyvek will not prevent moisture from entering the wall cavity from the outside. Both are vapor permeable and also most wall assemblies are not perfectly built and therefore moisture will get behind them, especially in the humid summer.

No offense Capt, but as a builder for 30 years you don't have many credentials. You are basically just saying I've just been doing whatever I was taught 30 years ago. I'm a licensed engineer with a pretty intense interest in building science because I plan to build a new super efficient house within the next couple of years. I'm not talking about googling and reading on forums. I'm talking about googling and reading papers by PhDs and Engineers who've been studying this sort of thing in response to building failures and the in pursuit of great, reliable buildings. The organizations Rockcam mentioned have published great information based on actual testing and science, I suggest you go read some instead of just preaching outdated practices.

 

[BlackTalon]

Blacktalon, these boys are talking about plastic/poly, that is a class 1 vapor retarder, AKA a vapor barrier.

Class I just means 0.1 perm or less. The term 'vapor barrier' has gone the way of the Dodo. It has been recognized that none of the materials/ systems were actually 'barriers'. Also, WRT the polyethylene, once all the fastener holes for the metal wall cladding go through it, it is a little less 'barrier' then then intended.

I'm a licensed engineer with a pretty intense interest in building science..

Hey, me too! And thankfully I get paid for it.

 

[p1capt]

No offense Capt, but as a builder for 30 years you don't have many credentials. You are basically just saying I've just been doing whatever I was taught 30 years ago. I'm a licensed engineer with a pretty intense interest in building science because I plan to build a new super efficient house within the next couple of years. I'm not talking about googling and reading on forums. I'm talking about googling and reading papers by PhDs and Engineers who've been studying this sort of thing in response to building failures and the in pursuit of great, reliable buildings. The organizations Rockcam mentioned have published great information based on actual testing and science, I suggest you go read some instead of just preaching outdated practices.[/QUOTE]

No offense taken JC, I stated I stated I didn't have any credentials except 30 years of building, just stating my opinion of what I know has worked for many years vs theory. I know it takes engineers to create progress but when there seems to be no clear cut answer as this thread is indicating I'll take tried and true. As I stated just an opinion. Take it or leave it. No offense intended.

 

[Rosco]

I live in a different climate, but have read everything I could find until my head hurts while building my garage. I also have the same exterior siding as you, and I finally decided on no interior vapor barrier, except in the bathroom ( upstairs apartment ) due to moisture from the shower.

We have severe humidity down here in the summer so my concern was moisture coming in from outside. I used a high quality caulk on every lap seam on the siding, windows etc., and I also sealed every stud cavity in the corners (where the stud meets the outside OSB) with a bead of foam insulation (like a bead of caulk) to keep any airflow from the outside coming in. Then I either used unfaced insulation, cellulose (in the apartment), or faced bat insulation with slits cut into the face to release moisture.

After all of my research I concluded that there must be a way for moisture to escape, either interior or exterior, or top plate. I have not seen a fool proof way to seal a wall cavity and keep moisture out when there are competing temperatures on either side.

 

[BlackTalon]

There has been a lot of uncertainty since energy prices shot up and insulaiton levels were increased in the Codes. the 2012 IRC finally laid down some pretty specific requirements.

Down in South Georgia I suspect you should have a VR on the exterior side of the insulation and probably noting on the interior side (sorry,too lazy to go dig through IRC to confirm).

 

[Rosco]

Down in South Georgia I suspect you should have a VR on the exterior side of the insulation and probably noting on the interior side (sorry,too lazy to go dig through IRC to confirm).

Yes, typical house wrap over the OSB

 

[familytruckster]

My inspector told me not to put a vapor barrier in the house I rebuilt. He said it turns the walls into a mold factory.

 

[JCByrd24]

In the typical house wrap/OSB exterior it is the OSB that is the vapor retarder not the house wrap. Most wraps are vapor permeable while OSB is a tight class 2 retarder. This works well in the south with no extra step needed. OSB taking over the very permeable board sheathing is the primary reason this whole discussion is happening. Even in cold climates by default we are putting a significant vapor retarder on the outside of house, to put one on the inside then can lead to trouble.

Blacktalon I was not intending to argue with you as I agree, but the title of the thread refers to vapor barrier as well numerous responders using that term as well. The penetrations in the poly certainly may lead to it's ineffectiveness as an air barrier but the reading I've done suggests that doesn't help it's drying potential much. In addition, most of those fasteners will be going into studs, not be out in the field.

I will also mention that dense pack cellulose contractors in this area have almost completely stopped using the reinforced poly products to hold in the cellulose in favor of a Insulweb or other more permeable products.

 

[kgbagent]

I have not seen a fool proof way to seal a wall cavity and keep moisture out when there are competing temperatures on either side.

This is the key. An impenetrable barrier that neither water nor air cannot pass through in a wall or ceiling assembly does not guarantee zero moisture.

Think about a glass of ice water sitting outside on a hot summer day. Condensation occurs on the warm side. Now think about that same ice water in a Styrofoam cup. It does not sweat like the glass. This is because the Styrofoam cup is better insulated.

If the quality and performance of insulation is sufficient such that hot and cold do not meet (dewpoint) you will not have a moisture problem. The old vapor barrier thinking ("warm side in winter") was introduced because old insulation sucked, a dewpoint was created in the wall...and this caused stains on interior drywall.

 

[BlackTalon]

'Warm side in winter' is for areas where there are more heating days than cooling days. For southern areas where cooling dominates, the VR should go on the outside (i.e., warm side in summer).

JCByrd24, I did not take it as arguing. In general the term vapor barrier is used a lot on this BBS, when that term is no longer valid and often leads to misunderstandings. VR science/ understanding has advanced a lot over the last couple/ few years, and people doing research via teh Googlz may find themselves getting confused when they go to search on VB products for purchase and can only find VRs.

 

[JCByrd24]

Blacktalon, Absolutely and I appreciate your effort to bring accuracy to the conversation.

KGB you statements are pretty accurate but could be misleading. A fibrous permeable insulation like fiberglass or cellulose installed in a typical manor absolutely relies on the VR and the air barrier. By typical I mean a regular 2x6 without exterior foam. In a cold climate for example the sheathing will be cold, the lack of an air barrier will greatly reduces the insulation a effectiveness by allowing convection currents and air leaks, the latter of which combined with the lack of VR will result in frost on the back of the sheathing. If you google minimum amount of exterior foam you will find guidance on the r-value of foam needed to prevent this given the climate and interior bay r-value. A warning though that code has been slow to adopt and these numbers can be found in the code, but there is also a section that encourages too little exterior foam to prevent condensation.

http://www.greenbuildingadvisor.com/blogs/dept/musings/2012-code-encourages-risky-wall-strategies

 

[benjamintmiller]

Here is an excellent PDF by the Building Science Corporation that has flowcharts for when a vapor retarder is required and what type: Vapor Barriers and Wall Design

Richland, MI is in IECC zone 5.
Certainteed's fiber cement siding has a perm rating of 2.6, and OSB has a perm rating of 1, so assuming your fiber cement is similar, your exterior wall assembly has a perm rating around 0.7: 1/(1/2.6+1/1)

You plan on leaving the building unheated at times, so that means the cavity side of the sheathing will get below 37 degrees, so the flowchart suggests you should use a class II vapor retarder. Fiberglass insulation with kraft facing will work, or a "smart vapor retarder" will work.

Polyethlyne sheeting is never required in IECC zones 5, 6, or 7, and I believe it is harmful most of the time. If you do not seal the vapor barrier perfectly everywhere, moisture-laden air will eventually condense in your wall and either rot the sheathing or cause mold to grow.