Vapor barrier question

[cabin fever]

Hi all

I live in Iowa and built a 1000 sq ft Shop. With 10ft walls.

Outside is osb covered with tyvek, and vinyl siding.

Im getting to the inside now and wonder if i need insulation with a vapor barrier. 2x4 walls 16oc. Im going to sheet the inside with osb and it will have 2-3 coats of white paint. Ceiling will also be insulated and done in metal. Metal roof if that matters at all

It will have heat/ac

Do i need kraft faced insulation on the inside?

 

[jabin]

In building science web site it has the vapor barrier on the inside or heated side of the building. I would use a vapor barrier but just one, meaning make sure your insulation doesn't have it if you adding it seperate.

 

[Bigshow0003]

If unfaced insulation, then yes, a minimum of 4 mil vapor barrier between the inside OSB and your insulation.

If faced insulation, then no vapor barrier needed.

 

[Jakemedic]

Hi all

I live in Iowa and built a 1000 sq ft Shop. With 10ft walls.

Outside is osb covered with tyvek, and vinyl siding.

Im getting to the inside now and wonder if i need insulation with a vapor barrier. 2x4 walls 16oc. Im going to sheet the inside with osb and it will have 2-3 coats of white paint. Ceiling will also be insulated and done in metal. Metal roof if that matters at all

It will have heat/ac

Do i need kraft faced insulation on the inside?

Hello from a fellow Iowan! Kraft face seen to work well. I have used it in prior projects. The new shop is a post frame. Thinking I may use un faced and vapor barrier. My outside is metal with housewrap.

 

[rburke65]

From what I know, yes....a vapor barrier on the inside. And don’t forget the ceiling....behind your metal.

 

[cabin fever]

Thanks all. Vapor barrier it is. I wasnt sure since i Used tyvek on the exterior.

 

[u2slow]

An inner and outer VB of plastic or tyvek is a sure way to encapsulate moisture in the wall and have rot/mold issues. You VB the warm side as the other guy posted.

But since you tyvek'd the outside, you need to use something that breathes better on the inside.

 

[tfinniii]

Face insulation needs to be sealed to stop vapor, You will be fine with those paint coats. Just be sure to seal any gaps as that will stop the water vapor, because you stop air infiltration from inside.

 

[kbs2244]

Tyvek "breathes"
It will pass water vapor.
It is a liquid water barrior

The OP needs a VB on the warm side of his walls

 

[nadogail]

May you enjoy your shop for many years, all of them in good health.

 

[cabin fever]

Thanks all. I bought the kraft faced insulation (paper faced). Tyvek is on the outside between the siding and sheeting. I think im good?

 

[850xpeps]

Kraft paper isn’t the way to go imo. And 6mil is the mine for vapour barrier. There’s certified poly for that. How do you seal all the joints in the kraft paper? You can’t. Poly over the Kraft paper If you want to keep it. That’s my advice. The tyvek on the outside is a moisture barrier and that’s how you build properly. Moisture barrier on exterior wall keeps water that gets behind siding out and let’s wall breathe.

 

[Leaflessshadetree]

Kraft paper isn’t the way to go imo. And 6mil is the mine for vapour barrier. There’s certified poly for that. How do you seal all the joints in the kraft paper? You can’t. Poly over the Kraft paper If you want to keep it. That’s my advice. The tyvek on the outside is a moisture barrier and that’s how you build properly. Moisture barrier on exterior wall keeps water that gets behind siding out and let’s wall breathe.

I seal the joints of paper backed insulation with tape. The same way I seal the joints with poly.

 

[Innovate1]

From what I know, yes....a vapor barrier on the inside. And don’t forget the ceiling....behind your metal.

One contractor I got a quote from noted on the quote that poly is not needed with the metal ceiling. Not sure that is right but that's what it said. I have seen poly vapor barrier mentioned other places behind metal ceiling so don't know which is right. If the metal is fairly tight you basically have two vapor barriers.

I am trying to get some other quotes.

 

[jabin]

Tyvek "breathes"
It will pass water vapor.
It is a liquid water barrior

The OP needs a VB on the warm side of his walls

tyvek is vapor permeability you're good there but, you must seal the kraft faced insulation to make it a sealed impermeable to water vapor.

 

[850xpeps]

I seal the joints of paper backed insulation with tape. The same way I seal the joints with poly.

That’s a lot of work. Sealing at every stud space. I don’t see the benefit. Also I don’t see how it can seal or insulate anywhere as near as good as the alternative.

One contractor I got a quote from noted on the quote that poly is not needed with the metal ceiling. Not sure that is right but that's what it said. I have seen poly vapor barrier mentioned other places behind metal ceiling so don't know which is right. If the metal is fairly tight you basically have two vapor barriers.



I am trying to get some other quotes.

We poly behind tin. As tin is not a vapour barrier by code, that I’m aware of.

 

[johnnyradiant]

Tyvek or 'tar paper' on the outside is not in place of vapour barrier it's as well as. I'd have to relook at the code but here we were 6 mil for vapour barrier. Maybe it has changed to a 4 mil.?

 

[Innovate1]

I talked to an insulation contractor today about vapor barrier, particularly in a metal ceiling. They said for my area no vapor barrier has been recommended since about 2008 for walls and ceiling. Part of the year the optimal place would be the inside of the wall and the other half it would be the outside. So either way you get condensation where you don't want it part of the year. They said for the metal ceiling no barrier is needed for fiberglass. For treated paper they recommend tyvek or similar building wrap to get the chemically treated paper off the metal because direct contact can cause corrosion but doesn't trap moisture. Seemed to know what they were talking about but really only applies to our climate. They said something about being in zone 4...