Need some vapor barrier and insulation advice

[Woody65]

I made the outside lights out of black pipe. Couldn’t find anything I liked that was at a reasonable price. Needed 10 lights for the outside. Decent ones were $200 a piece. Made ones for $50 a piece. Don’t have a good pic of them up close.

 

[Rockbadchild]

So, I built a 32x40x12 pole barn 6 yrs ago with no intention of heating it. I did not put any house wrap under the board and batten siding. I am preparing to stud the walls and use either rock wool or fiberglass insulation in the walls and blow in insulation in the ceiling. The interior walls will be made of galvanized corrugated metal for the bottom 4’ and ship lap wood for the top 8’. My question is should I put vapor barrier on the inside of the studs underneath the wall covering? My instinct tells me not to. It seems the warm air on the heated interior will meet the cold air in the wall and condensate. I could be wrong.

the vapour barrier need to be on the heated side of the building … and it is use to keep the insulation free of condensation since some insulation like fibreglass loose R value when wet.

 

[Woody65]

Rock wool advantage is sound control. A rock wool room is shockingly quieter (of outside noise) than a fiberglass insulated room. In a garage environment, sound control may be of no advantage to you - and purchase should be based on other factors - price, availability, ease of installation. The following from a study done on the Permeance of Steel Roof Decks and Effect on Hygrothermal Performance of Roofing Systems Joseph P. Piñon, PE Raymond W. LaTona, PhD, both members of ASHRAEA. "Although the field of the steel deck is impermeable, the side and end laps contain gaps that permit water vapor and air to pass through the deck."
What that means to you Woody, is you should absolutely NOT put a vapor barrier behind the metal sheathing. However, you should seal each piece of metal you install, so no air gets around the openings. The insulation purchased at HD will either be unfaced (no vapor barrier), or will have either a asphalt impregnated paper face (vapor barrier), or an aluminum face (good vapor barrier). You want the first one for insulation behind the metal.

You write " My instinct tells me not to. It seems the warm air on the heated interior will meet the cold air in the wall and condensate. I could be wrong."
Your statement related to condensation is correct, but that would mean you SHOULD vapor barrier - not go with your instinct 'not to". Maybe your fingers got confused.
You need to vapor barrier behind the ship lap, and keep any air from getting past the ship lap and down behind the corrugated metal at the bottom.

I like xrjohndeere's suggestion. But that won't be cheap. It's not typically a DIY job.

Good luck with it.
Eric

Hey Eric. I was planning on using 1/2” osb behind the galvanized steel. Does this make a difference on how I would need to insulate.

I got all that you said above and it makes sense to insulate differently behind the metal and ship lap.

Thanks

 

[PILOON]

Normally the vapor barrier on insulation goes toward the inside of the building. I would go with a vapor barrier if you plan to insulate and heat.

Sealed with tape!
Metal will always sweat and the insulation will soon absorb the moisture and rust the metal.
I once on a project observed as to how bad that moisture could do a number on metal roofing since the guy had placed the tin directly on plywood.

In fact I have a small shed that you'd swear ,come spring and snow on the roof, that it is raining inside, it can be that bad.

 

[ROUSTABOUT]

Vapor barrier goes toward treated air. No vapor barriers touching each other. If using two layers of insulation the vapor barriers go to inside.

 

[Have tractor did travel]

Hey Eric. I was planning on using 1/2” osb behind the galvanized steel. Does this make a difference on how I would need to insulate.

I got all that you said above and it makes sense to insulate differently behind the metal and ship lap.

Thanks

Woody, OSB is available foil backed and NON foil backed. You want NON foil backed.
Roustabout is correct about insulation, in northern latitudes (Georgia and north) when faced, the facing should face the treated air. HOWEVER, if using 2 layers of insulation, the layer closest to the outside should be unfaced. The layer closer to the treated area, should be faced. (This is not you Woody - your metal is the vapor barrier). The objective is to have only one vapor barrier. If there are multiple vapor barriers, then moisture may get caught between the vapor barriers and cannot get out - encouraging mold, etc.
In your case Woody, my concern was with outside metal, and inside metal - would there be an envelope in which moisture laden air could not get out ? I felt that if you did a good job sealing the inside metal, that any air that got past, any moisture in that air could escape through spaces in the outside wall, since it wouldn't be sealed as I encouraged you to do to the inside wall.

 

[CADplans]

Woody, when you think about it,, the insulation has a large temp differential (hopefully!!)

The interior wall, whatever it is, and the vapor barrier will have almost zero temp delta from inside to the insulation.

If the interior wall, and the vapor barrier had a large delta temp, you would not need insulation.
So, the sweating on the cold side of the vapor barrier will not occur.

My cousin had a rental house in Pittsburgh PA,,
The exterior was wood, with paint.
Right where the bathroom was, the outside paint would bubble up, and come off.
The moisture from the bath/shower went right through the outside wall.

He had to add a vapor barrier to stop the paint from peeling on the outside of the home.
IIRC, he only fixed the bathroom, not the whole house.

That home was probably built in the VERY early 1900's, probably before 1910.
I doubt they even thought about a vapor barrier,,

 

[Woody65]

Woody, OSB is available foil backed and NON foil backed. You want NON foil backed.
Roustabout is correct about insulation, in northern latitudes (Georgia and north) when faced, the facing should face the treated air. HOWEVER, if using 2 layers of insulation, the layer closest to the outside should be unfaced. The layer closer to the treated area, should be faced. (This is not you Woody - your metal is the vapor barrier). The objective is to have only one vapor barrier. If there are multiple vapor barriers, then moisture may get caught between the vapor barriers and cannot get out - encouraging mold, etc.
In your case Woody, my concern was with outside metal, and inside metal - would there be an envelope in which moisture laden air could not get out ? I felt that if you did a good job sealing the inside metal, that any air that got past, any moisture in that air could escape through spaces in the outside wall, since it wouldn't be sealed as I encouraged you to do to the inside wall.

Eric, I don’t have metal on the outside, it’s wooden board and batten siding. Don’t know if this makes a difference.

 

[Woody65]

Vapor barrier goes toward treated air. No vapor barriers touching each other. If using two layers of insulation the vapor barriers go to inside.

Roustabout,
I have heard of people, to save money, have 1” of closed cell foam sprayed on and then use either fiberglass or rockwool on top towards the inside wall to get more R value. Does this constitute 2 vapor barriers?

 

[ROUSTABOUT]

Roustabout,
I have heard of people, to save money, have 1” of closed cell foam sprayed on and then use either fiberglass or rockwool on top towards the inside wall to get more R value. Does this constitute 2 vapor barriers?

Yes but it's fine as long as two vapor barriers are not touching each other. Putting the batts over the foam is fine as long as the insulation paper is toward living space. Foam is toward outside wall. I have done exactly that a few times.