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Old 04-02-2011, 10:32 AM   #1
Cougar
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Default Vapor barrier in garage ceiling

Want to finish the attached garage.
When the house was built they rocked the firewall and ceiling in the garage.
But they didn't put a vapor barrier in the ceiling.
Want to insulate everything, what's the best way to install a vapor barrier in the ceiling after it's been rocked.
Thanks
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Old 04-02-2011, 10:53 AM   #2
rickairmedic
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Default Re: Vapor barrier in garage ceiling

Take the sheetrock down put up the vapor barrier then put new sheetrock up . I will ask are you planning to heat the garage if so I wouldnt worry so much about a vapor barrier .


Rick
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Old 04-02-2011, 12:35 PM   #3
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Default Re: Vapor barrier in garage ceiling

even if you are heating the garage, is it a big deal not to have one? My house was built in 1973, I don't have a vapor barrier in the house. I bought nsulation with a vapor barrier for the garage though.

I would make sure the garage is vented good, and move on with your life.
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Old 04-02-2011, 12:35 PM   #4
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Default Re: Vapor barrier in garage ceiling

I think they may paint that is a vapor barrier.
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Old 04-02-2011, 12:58 PM   #5
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Default Re: Vapor barrier in garage ceiling

My house was built in 65 they didnt even know what insulation was then much less vapor barrier . I have installed kraft backed batts as I have worked on the house removing and replacing drywall.

Rick
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Old 04-02-2011, 01:01 PM   #6
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Default Re: Vapor barrier in garage ceiling

This thread prompts me to ask.... I you build or reside your garage or house and you use Tyvek on the outside of the structure is that a vapor barrier or is it just for air infiltration......
I know when I put insulation in with kraft paper I staple the flanges to the studs and the room looks like a giant paper bag... If that is a so-called vapor barrier how does that interact with the outside tyvek....
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Old 04-02-2011, 01:08 PM   #7
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Default Re: Vapor barrier in garage ceiling

TYVEK IS BOTH---it does breath if installed properly
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Old 04-02-2011, 03:16 PM   #8
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Default Re: Vapor barrier in garage ceiling

My understanding is that Tyvek is an infiltration barrier but not a vapor barrier. If it was a vapor barrier; putting it on the outside (cold side as designed) would trap moisture in your walls and eventually do serious damage.

As long as you have adequate ventilation above your ceiling you should be good to go. You will likely find a 50/50 mix of opinions on this topic. Walls, yes. Ceilings, no (with proper ventilation).

Just finished the final barrier on my walls in my garage. Used some 6 mil poly left from when the concrete was poured and covered.
Ken
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Old 04-02-2011, 03:52 PM   #9
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Default Re: Vapor barrier in garage ceiling

Over and over again.

Vapor barrier vs. moisture barrier.

Tyvek is a MOISTURE barrier.
Moisture is LIQUID water.
Tyvek is, by design, vapor permeable.
That means it will let vapor through.
Its purpose is to keep any rain (liquid) that gets through the siding from getting into the wall.
It is also used as a wind barrier.

Vapor is water as a gas.
We call it humidity.
Poly and well sealed Kraft (nobody does it correctly) are vapor barriers.

Water vapor will, by its nature, go to cold.
As far as it can, before condensing.

You want a vapor barrier on the warm side of the wall to keep any humidity generated inside from getting into the wall in the first place.
But if some gets into the wall, you want it to pass through the insulation, AND the moisture barrier, to the outside siding. There it will condense and drain down the inside surface of the siding and out the drain holes that should have been part of the siding job.

Even brick sided wall will have “weep holes” in the bottom row of bricks.

This is why the south side of a wood sided house will have problems with the paint peeling.
The sun will keep the siding warm enough so the vapor will not condense.
But nobody ever vents the top of a siding job. So the vapor cannot escape and goes through the siding, popping the paint off in the process.

A roof, especially a black one, is an extreme case of the south wall problem.
Keep as much vapor out of it as you can.
But allow lots of venting above the insulation, both IN as well as out, for the vapor that does get through.
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Old 04-02-2011, 04:40 PM   #10
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Default Re: Vapor barrier in garage ceiling

you dont want vapor barrier on ceiling, moisture rise and collect on the plastic, rotting out the sheetrock. Just let it pass, not hurting anything
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Old 04-02-2011, 07:36 PM   #11
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Default Re: Vapor barrier in garage ceiling

Thanks for the replies.
Yes, no, maybe. That narrows it down.

It will be a bit before I get to it. When I do maybe I'll put on a couple coats of the vapor barrier primer paint and be done with it.
It is vented good with a continuous ridge and soffit vents.
May heat occasionally.
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Old 04-02-2011, 07:42 PM   #12
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Default Re: Vapor barrier in garage ceiling

Quote:
Originally Posted by rickairmedic View Post
Take the sheetrock down put up the vapor barrier then put new sheetrock up . I will ask are you planning to heat the garage if so I wouldnt worry so much about a vapor barrier .


Rick
Wouldn't it be even MORE important if you where going to heat the garage? That would cause a ton of moisture from the cars steaming/melting/rain water evaporating.... I'd vapour barrier and have an exhaust fan (as I do now).

Quote:
Originally Posted by brownbagg View Post
you dont want vapor barrier on ceiling, moisture rise and collect on the plastic, rotting out the sheetrock. Just let it pass, not hurting anything
\

WHAT???? You put VB to stop the moisture from contacting the insulation. Wet insulation = MOLD.
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Old 04-02-2011, 08:10 PM   #13
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Default Re: Vapor barrier in garage ceiling

E tec how did you get all that stuff on the cars in your garage . I thought yours was like mine storage for the toys and workshop . There shouldnt be any of that stuff on the cars in there .


Rick
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Old 04-02-2011, 08:31 PM   #14
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Default Re: Vapor barrier in garage ceiling

kbs2244...well, do we put a VB on the ceilings? You sound knowledgeable...
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Old 04-02-2011, 09:06 PM   #15
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Default Re: Vapor barrier in garage ceiling

My house has no vapor barrier, and I do heat it.
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Old 04-02-2011, 10:06 PM   #16
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Default Re: Vapor barrier in garage ceiling

if there is no living spaces above the garage (bedroom ,living room)remove the drywall,insulate the ceiling,use 6mil poly for vapor barrier,drywall with 5/8 alot of building codes call for 5/8 drywall in a garage on ceilings and wall abutting living spaces.hope it helps.or just call your building dept and ask one of thir inspectors most are helpful then again there is always the one dick head there. lol
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Old 04-02-2011, 10:13 PM   #17
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Default Re: Vapor barrier in garage ceiling

My 24 X 30 has 2 X 6 sidewalls, so I put R-19 unfaced fiberglass in the walls. I then put on 10 mil clear plastic and then 1/2" OSB for interior wall sheathing. For the ceiling I stapled up the 10 mil plastic, and then sheathed the ceiling with OSB. This afternoon we blew in around 16" of cellulose, so now my garage is fully insulated.

While I was installing the sheathing on the walls, it was pretty cold and windy. The plastic vapor barrier made a lot of difference. I have the outside walls covered with houswrap and have just begun installing the siding.
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Old 04-02-2011, 10:16 PM   #18
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Default Re: Vapor barrier in garage ceiling

Quote:
Originally Posted by mrpaco69 View Post
if there is no living spaces above the garage (bedroom ,living room)remove the drywall,insulate the ceiling,use 6mil poly for vapor barrier,drywall with 5/8 alot of building codes call for 5/8 drywall in a garage on ceilings and wall abutting living spaces.hope it helps.or just call your building dept and ask one of thir inspectors most are helpful then again there is always the one dick head there. lol
I dont think I would do that unless you plan on permitting the job. You may open a can of worms that would be best left closed, not saying you shouldnt permit it,or that you should,just ,well, you can use your imagination.
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Old 04-02-2011, 10:18 PM   #19
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Default Re: Vapor barrier in garage ceiling

Quote:
Originally Posted by Berserker View Post
My house has no vapor barrier, and I do heat it.
But that doesnt make it right.... Our undertanding of building envelope technology has come a llllooong way in 20 years.>>>>>

Quote:
While I was installing the sheathing on the walls, it was pretty cold and windy. The plastic vapor barrier made a lot of difference. I have the outside walls covered with houswrap and have just begun installing the siding.
EXACTLY. Another good reason for VB - it's a systems approach.

Last edited by e-tek; 04-02-2011 at 10:20 PM.
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Old 04-02-2011, 10:22 PM   #20
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Default Re: Vapor barrier in garage ceiling

Quote:
Originally Posted by rickairmedic View Post
E tec how did you get all that stuff on the cars in your garage . I thought yours was like mine storage for the toys and workshop . There shouldnt be any of that stuff on the cars in there .


Rick
You mean rust?
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