Vapor barrier - house wrap 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:

Thanks guys!!!

 

[tthopskin@yahoo.ca]

nice shop tyvex . it helps with holding the isolation in place and the heat and plastic inside ya . and for your heat just put a pic of steal tin 1/2 from the wall and strap it 1/2 off the floor the cool air will run behind it and you will never melt the plastic ..it will never get hot behind the steel ..even if it is on the ceiling keep a space between the steel and let the air through it it will make its own draft and keep cool behind it i hope this will help

 

[Qapla]

On the building/houses they build here they put the OSB/sheathing on the outside of the wall, then the Tyvek - and completely wrap the building/house.

 

[SSdoxie]

I like to use 6mil poly for vapor barrier on large walls like this. 4 mil does the job but the 6 mil is easier to stretch tight & staple without tearing holes in it. Don't put a vapor barrier on both sides of the insulation but Tyvek would work, it is a wind barrier but does "breath". The Kraft faced is a vapor barrier it self so if stapled in smooth with no rips, poly is not supposed to be required, but we always used it anyway in the houses we used to build. You could also cut slits in the kraft face to let is breath, install the paper side towards the outer wall against the outer steel then poly on the inside.

 

[inane2]

Thanks for the responses guys.

The 6 mil makes sense on handling it vs the 4 mil. I have quite a bit of 6 left over from another concrete pour. This would be a good place to use it.

 

[BeezFun]

Since you live in Kentucky, your vapor barrier should go on the outside of the insulation, not the inside, since your predominant climate is humid and hot. Now if you live in the mountains and the weather is more mild and you have some cold weather in the winter, might want to put the barrier toward the living space. Kraft facing is considered class II vapor retardant, which is more than the IRC requires or recommends for your area, so you should put that against the exterior wall. If you haven't bought the insulation yet, I'd get it unfaced. The insulation manufacturer's guidance is to avoid any class I retardant (like poly) in warm climates because of condensation complications.

 

[inane2]

Thanks BeezFun. Great info. I live in central KY, gets cold in the winter, but our summers are very hot and very humid.

I did already buy the insulation. It's Owens Corning EcoTouch R-19 kraft faced batts. 15" wide by 6.5" deep. If I skip the poly and housewrap both, do you recommend putting the Kraft facing against the metal and the fiberglass against the OSB?

 

[BeezFun]

Thanks BeezFun. Great info. I live in central KY, gets cold in the winter, but our summers are very hot and very humid.

I did already buy the insulation. It's Owens Corning EcoTouch R-19 kraft faced batts. 15" wide by 6.5" deep. If I skip the poly and housewrap both, do you recommend putting the Kraft facing against the metal and the fiberglass against the OSB?

I'd study this page. I would have said use housewrap, but since your siding is on it's hard to do that now. Steel siding really likes to condense moisture, so it's not ideal to have insulation right against it, but you can minimize that problem by making a really good air barrier out of the OSB. I'd caulk the OSB joints and foam any larger openings along floor or top sill, that will make the OSB your air barrier. Since you plan to heat the structure in winter, and I assume will not air condition it in summer, I think I'd put the kraft facing against the living space, especially since you have cold winters. You'll never have any hot exterior summer air hitting a cold living space, so there shouldn't be any condensation in the summer.

If there's any chance you could exchange that fiberglass for foam board insulation, I'd do that. Moisture is not a problem with the foam board and it also stops air migration if it's installed well. It's much more forgiving when you use it with steel.

 

[TCJatko]

I always thought house wrap let inside moisture out but didn't let outside moisture in. The outside sheathing is metal and theoretically impervious. If you put tyvek or some such up against it won't that tend to concentrate moisture inside the sheet metal? Usually outside walls are T-111 or siding or clapboards or brick or some other semi-permeable material.

 

[farmall40]

I always thought house wrap let inside moisture out but didn't let outside moisture in. The outside sheathing is metal and theoretically impervious. If you put tyvek or some such up against it won't that tend to concentrate moisture inside the sheet metal? Usually outside walls are T-111 or siding or clapboards or brick or some other semi-permeable material.

100% agree.