Interior remodel - vapor barrier question!

[inane2]

Hey guys!

Slowly working on remodeling a 36'x48' shop that was on my property when I moved here. A little about the building up front :

- 5.5" concrete slab
- Trusses on 6' centers
- 2x6 girts (flat) on 30" centers
- White ribbed metal panels on the ceiling, 10' tall
- No soffit on either end on the building, trusses were cut flush with the posts
- Heated by a barrell wood stove

I went back in and replaced metal on two sides of the building due to damage and very badly faded, chalky paint. Once the new metal was up, we went in and toe-nailed in 2x6 bookshelf girts on top of the flat girts (still retaining 30" centers).

I've bought R-19 batts, 15" wide and 6.5" deep, kraft faced. These will fit perfectly between the new girts. Once installed, going to cover the walls with 7/16" OSB. The corner where the barrell stove resides will get white metal instead of OSB.

I went ahead and bought new metal for the roof. It will be spring before it's installed unless we get a nice weekend sometime soon. Before laying the new metal roof down, I'm going to install "Low-E" radiant barrier. 1/4" thick, basically double bubble with aluminum foil on both sides. This will be installed over the purlins, beneath the new metal. Also, there is currently insulation batts between the trusses, on top of the metal ceiling. This stuff is in rough shape, so I'm going to remove it and use blow in insulation.

Two questions:

1. Should I install a plastic vapor barrier over top the batts in the wall before I install the OSB (or metal in the stove corner)? Any recommended thickness?

2. Should I install tyvek or house wrap against the inside of the metal before I install the batts in the wall cavities? Looking back, I had a perfect chance to do this when the metal was off. I've read different opinions on having bare fiberglass against metal panels.

To help you visualize, here is a pic before I installed new metal and bookshelf girts:

View media item 23543

Thanks guys!!!

 

[kbs2244]

Poly on the warm side.
It is a vapor (gas) barrier.

Tyvek on the cold, or outside.
It is a moisture (liquid) barrier.
(If you notice, it says it is "vapor permeable." That means vapor will go through it.)

 

[inane2]

Thanks for the reply!

 

[Kevin C]

Tyvek allows moisture across it, but assuming your metal wont let it past the tyvek, so I cant see it doing a lot for moisture control. It could help with air infiltration.

That said, a barrier on the inside of the walls ( like poly) will prevent the wall from drying to the inside. That could be an issue since it would seem like they wont dry to the outside either ( metal shell).

If you had a 1" air gap between the metal shell and the building wrap / insulation you would have a way to let trapped water evaporate. In that case tyvek on the outside or poly on the inside would make sense. That would be the ideal system.

In Oregon the new code for occupied structures requires a 1" drain plane on the outer wall.

Since you have a shop moisture buildup from cooking and showering is not a big issue, but trapped moisture in the wall could be.

Where I live it rains a lot and gets pretty damp. Depending on your climate this may not be as big an issue.

Just putting poly on the inside may be a good enough.

Some info: http://www.greenbuildingtalk.com/Forums/tabid/53/aff/14/aft/79388/afv/topic/Default.aspx

That's my take... fire away.

 

[inane2]

Nice read, thanks Kevin.

Insulation always seems to be a "hot" topic, especially in our pole buildings. Thanks for your advice!

 

[inane2]

New pics .....

View media item 26290

View media item 26291

 

[clarkebd]

So, dumb question as I'm dumb to this.

What is the point of a plastic barrier before putting drywall up on a GARAGE wall?

I get that you need it for an interior living space to keep moisture out, but on a garage wall to the outside, and if the area isn't heated.

So, example my garage. Existing Outside garage wall. OSB and tar paper with siding over it. If I insulate that wall and want to put up drywall then, why do I need the barrier? Is it to keep the drywall from molding?

 

[kbs2244]

You want tp keep the vapor from getting into the insulation and the condensing into moisture.
That leads to loss of insulating ability, mold, and other bad stuff.