I have a 38 x 52 stick frame bulding that is just geting finished. 2x6 wall construction with pro-rib metal on the outside walls and roof, soffit vent with a ridge vent. It has radiant floor heat & 2" closed cell spray foam on the walls. Interior of bulding is also going to be lined with metal including the ceiling. I want to blow in R-40 loose fiberglass on top of the ceiling tin. Do I want to install a vapor barrier above the ceiling tin in this appication? I do have a wash bay in there also if that maters.
Vapor barrier for ceiling necessary?
- Thread starter dschmit
- Start date
rburke65
Well-known member
I believe that yes, you would want a vapor barrier on the ceiling before installing the metal liner.
wildstyle
Well-known member
Yes, vapor barrier is needed.
volleyball
Well-known member
Spray 2" of hi density foam and you'll have a vapor barrier
wildstyle
Well-known member
Poly is cheap. Just vapor barrier and insulate as you were going to.
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What if you used cellulose?
I will be blowing R60 cellulose in my pole barn shop ceiling and wasnt planning on using any other vapor barrier. The walls will be sprayed with closed cell foam like the OPs.
http://http://www.regalind.com/pdf/vaporbarrier.pdf
I will be blowing R60 cellulose in my pole barn shop ceiling and wasnt planning on using any other vapor barrier. The walls will be sprayed with closed cell foam like the OPs.
http://http://www.regalind.com/pdf/vaporbarrier.pdf
sands35
Well-known member
The cellulose gets blow in after the ceiling is up. Still need a vapor barrier though. Stapled up sheet plastic works great.
Highbeam
Well-known member
Why so much desire to skip the ceiling poly? It is cheap and easy. Dont just do it for moisture migration, do it for air sealing to keep all the heated air from flowing out through the roof. Don't you guys close your windows when it is cold out? Thats not for moisture control, it's so you dont let all the heat out.
GYPSY400
Well-known member
X2! Anything other than spray foam requires vapour barrier.. Be sure to tape all seams and acoustic seal all wood joints.. The building will need to be sealed like a ziplock bag to be effective.
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OK, I need an education. I always thought a vapor barrier was to prevent migration on interior moisture into the insulation. Some paints also function as a vapor barrier, to be used in retrofitting insulation in older contruction.
That said, since a metal ceiling is impervious to moisture migration, why is an additional barrier recommended? And what is the source of the recommendation?
Seems to me this is a situation where any moisture that may make it past the metal seams would wind up condensing between the metal and plastic.
Not arguing, just asking???
That said, since a metal ceiling is impervious to moisture migration, why is an additional barrier recommended? And what is the source of the recommendation?
Seems to me this is a situation where any moisture that may make it past the metal seams would wind up condensing between the metal and plastic.
Not arguing, just asking???
OccupantRJ
Well-known member
I am thinking like you are on this. I have no windows in my shop, and will be installing a metal ribbed ceiling with blown fiberglass insulation. I am trying to decide on whether to install a vapor barrier above the ceiling.
Rookie2
Well-known member
This will freak you out ! I built a Morton bldg. metal walls inside & 4'x4' x1" fiberglass drop ceiling with 6" fiberglass on top. METAL ROOFS cause RAIN inside ! I've closed down the sofit vents ,i've opened 2'x2' vents on end walls plus 60' ridge vent. METAL ROOFS **** !
rburke65
Well-known member
I'm still believing that you first staple the plastic sheeting to the bottoms of the trusses or ceiling joists, install the metal liner, blow in or place your insulation.
Highbeam
Well-known member
A continuous sheet of metal is a vapor barrier. Dont be silly, your metal ceiling will NOT be continuous or air tight.
wildstyle
Well-known member
Exactly..it is an air and vapour barrier.
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dirttracker18
Well-known member
As already stated, the vapor barrier is not just to stop the migration of moisture, which your metal will NOT do. It stops the migration of air that is carrying your conditioned air away. All insulations, except closed cell foam, will allow air to travel through them. Hold up a batt of insulation between you and a blowing fan! Insulation attempts to stop the transfer of heat or cold, not air movement. The stopping of air movement is the just of the vapor barrier.
danski0224
Well-known member
Use of a vapor barrier, placement of vapor barrier and the type of vapor barrier is dictated by climate zone.
You should really do your own research.
Walls: http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design
Ceilings: http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation
dirttracker18
Well-known member
It would have been cheaper and better to use real 6 mil poly for a vapor barrier. Tarps will disintegrate over time.
6 mil poly is very cheap and the correct material to use
The first one I did with a tarp was over 30 years ago and the tarp still looks like new. And it don't rip when putting up by myself. Just a dumb farm boy!!
dirttracker18
Well-known member
volleyball
Well-known member
HF blue tarps don't hold water.
rburke65
Well-known member
I'd use the 6 mil. The bigger the better...less seams. I made a "T" out of 2x4s, as a prop. Cut it the height of your ceiling plus ?? An inch. Use this to prop up the hanging plastic sheet to reduce the weight of the piece you are placing. Less rips..... Really el sane you are by yourself.
Flexia
Well-known member
Will 6mil plastic be strong enough for blow in insulation?
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Highbeam
Well-known member
Not alone, you then put a ceiling in to support the poly.