I am putting in a metal ceiling, where/how does the vapor barrier go?

gsganzer · Dec 30, 2016

I did something similar in my in-law apartment which is all pipe construction. I welded 2" purlins spanning between the underside of the trusses (for a flat ceiling). I then attached weathered currugated to the underside of the purlins as the ceiling to the apartment. My ceiling insulation is 6" vinyl backed roll insulation (6' wide) with the vinyl down (towards the climate controlled space).

johneic · Dec 30, 2016

I guess I did not make myself clear, I am sorry, I understand the plastic will go between the metal and the insulation, my question is:

"Does the plastic go above or below the lower 2by of the truss"

TnAndy · Dec 30, 2016

As I previously stated, staple it to the bottom of the lower truss cord 2x.....so when you look up, you see plastic first, then the truss above it. Then put your metal on right over the plastic.

If you put it above that lower 2x, and blow insulation in...and it seems like that would be a real pain in the backside to do..... you'll end up with voids places next to the 2x because the plastic would hold the insulation up at that point, and it would stretch and sag in the middle down to the backside of the metal ceiling.

If you looked at the insulation from above, it would either look like rolling hills, the 'hill' being the top side of truss bottom cord, or if you spray enough in to level it out, the center points will be REAL thick insulation, and not so much as it goes back up to the truss cord....so you might have 7-9" (or more) in the center, and maybe 2" on top the truss cord.

teejk01 · Dec 30, 2016

johneic said:
I guess I did not make myself clear, I am sorry, I understand the plastic will go between the metal and the insulation, my question is:

"Does the plastic go above or below the lower 2by of the truss"

Mine is on the bottom of the chord. I think you'd defeat the whole purpose the other way. The poly comes in pretty wide rolls and 2 people can get it done in no time at all...3 people would be better yet.

RNeumann · Dec 30, 2016

I looked at your profile and see you are in KY. I haven't built or designed in that state but I don't think the vapor barrier is common to your area. The metal will do the job (as someone above stated) and if you insist you could add some type of sealant (roll caulking or a polyurethane caulk) to the metal seams. Don't waste the time with the plastic- it's sort of old school thinking.
You Don't Need a Vapor Barrier (Probably)

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Something from these folks or similar can also guide you if you are so inclined-

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Don't forget to add soffit venting and protect that prior to insulation. Ridge or gabble vents will also be required but I assume you have that.

Any metal that gets near the cold zone or is in the cold zone will condensate- it will be interesting to see how this application works out as it could be tough to without a good plan ahead of time....