Visquine AND Paper-Faced Insulation Batts?

[BevoZ06]

I am going to insulate a detached garage that will not be heated or cooled. Someone has suggested that I should cover the walls and insulation with Visquine prior to installing the wall sheathing. I am planning to use insulation batts that are faced with the brown Kraft paper. I did not think I needed to use both. What do you think?

Also, should I staple the Kraft paper to the inside or to the outer edge of the wall studs? If I staple to the outer I could overlap somewhat the batts, but it wouldn't be as smooth a surface to install the wall sheathing to.

Thanks.

 

[5lima30]

Do not cover the craft paper batts with visquene! This will cause moisture to condensate inside your wall which is not good! YMMV.

 

[bczygan]

Kraft paper makes a less than ideal vapor barrier. Either use unfaced batts or slash the kraft paper, but use visqueen for the barrier.

 

[kbs2244]

bczygan has the idea.

The paper faced insulation is a lot easier to work with.
But if you are going to use plastic you do not want the vapor barrier it provides.
Put it up, then use a razor knife to slash the paper, then do a good job with the plastic.

 

[BevoZ06]

Thanks, everyone. I was leary of two separate vapor barriers.

Also, I learned the proper spelling of Visqueen.

 

[Mavawreck]

I wouldn't use Visqueen. Everytime I come across it there is moisture trapped inside the wall. I believe its use as a vapor barrier is more prevalent (acceptable) up north. I do not know what climate zone Austin is in but I believe the correct method of addressing this would be with a tyvek wrap on the outside. Best bet would be to call the local inspector and get their take on the situation.

 

[Mavawreck]

Also, it is quite easy to remove the craft paper backing from insulation batts. I do it all the time. I wouldn't even bother with slashing them, just peel it off.

 

[BevoZ06]

Mavawreck,

Thanks, but it's too late for the Tyvek. The garage is 19 years old, but is unfinished inside. During the summer the garage regularly gets up to about 120 degrees. During the winter it drops to whatever the ambient temperature is. I am hopeful that I can moderate these temps, especially in the summer, by insulating and finishing off the walls. It has no windows, so I am installing two windows to get some cross-ventilation.

 

[Mavawreck]

http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design

I think that should answer your question by page 5.

"The recommendations are based on the following principles:
• Avoidance of using vapor barriers where vapor retarders will provide satisfactory performance. Avoidance of using vapor retarders where vapor permeable materials will provide satisfactory perfor- mance. Thereby encouraging drying mechanisms over wetting prevention mechanisms.
• Avoidance of the installation of vapor barriers on both sides of assemblies — i.e. "double vapor barriers" in order to facilitate assembly drying in at least one direction.
• Avoidance of the installation of vapor barriers such as polyethylene vapor barriers, foil-faced batt insulation and reflective radiant barrier foil insulation on the interior of air-conditioned assemblies — a practice that has been linked with moldy buildings.
• Avoidance of the installation of vinyl wall coverings on the inside of air conditioned assemblies — a practice that has been linked with moldy buildings.

Each of the wall assembly design recommendations were evaluated us- ing dynamic hygrothermal modeling. The moisture content of building materials that comprise the building assemblies all remained below the limiting-equilibrium moisture contents as specified in ASHRAE 160 P under this evaluation approach. Interior air conditions and exterior air conditions as specified by ASHRAE 160 P were used. WUFI was used as the modeling program."

Lots of good reading there.

 

[green.bubbly]

This has been an ongoing debate for a long time. The problem is the different zonal conditions, defining what if a barrier versus a retarder and whether or not the building will be conditioned or not.

So I do not have an answer and I doubt you will find a cut and dry answer on the Internet. As one person mentioned, check with a local building inspector.

 

[wrenchguy]

"I am going to insulate a detached garage that will not be heated or cooled."
WHY???

 

[BevoZ06]

"I am going to insulate a detached garage that will not be heated or cooled."
WHY???

That's a reasonable question. It's because if, some years from now I decide to condition the air, I will kick myself for not insulating the walls prior to closing them up. Insulation is cheap and easily installed, so I had better do it now or never. I do think I will get some small relief from the hot Texas sun in the summer with the insulation and two windows installed for some cross ventilation.

 

[larry4406]

Here in northern VA all of the production homes my company built were all done with tyvek exteriors, caulked joints for air seal, and fiberglass batts with kraft paper. The Kraft paper goes to the warm (heated) side.

I have no experience with plastic sheating but believe it would promote formation of condensate, at least here in No. VA, and would not use it.

 

[The Lazy Destroyer]

"I am going to insulate a detached garage that will not be heated or cooled."
WHY???

Are you saying this will not have any noticeable effect? I'm assuming this would still cut down on the extreme temperatures a bit?

I have a 25x40 detached uninsulated/unconditioned garage in Georgia and I am hoping to get a ceiling and insulation (walls and ceiling) added soon. I do not expect it to make things perfect but assuming that it will minimize the "extremes" that the garage sees throughout the day. Basically that it will stay closer to the average daily temperature throughout the whole day as opposed to being so cold in the morning and warm in the afternoon.

Getting it conditioned is not in the budget for the next year or so, so with the insulation (and adding fans soon as well) that it may make it a little better than it is now.

 

[bigdav160]

Are you saying this will not have any noticeable effect? I'm assuming this would still cut down on the extreme temperatures a bit?

It's a continuous debate. Insulation slows the transfer of convection energy, and in some installations conduction energy, because the air trapped in the insulation isn't good at transferring heat. It's really designed to control heat loss.

In the sunny south, heat gain is the problem not heat loss. Much of this heat gain is caused by radiant energy from the sun. Regular insulation has little resistance to this radiant energy. For this application, a radiant barrier should be installed.

For our southern members, if the space is not climate controlled or passively cooled, insulation can be a detriment.

flame away

 

[BevoZ06]

It's a continuous debate. Insulation slows the transfer of convection energy, and in some installations conduction energy, because the air trapped in the insulation isn't good at transferring heat. It's really designed to control heat loss.

In the sunny south, heat gain is the problem not heat loss. Much of this heat gain is caused by radiant energy from the sun. Regular insulation has little resistance to this radiant energy. For this application, a radiant barrier should be installed.

For our southern members, if the space is not climate controlled or passively cooled, insulation can be a detriment.

flame away

I won't be putting a radiant barrier on the walls. If I later decide to close the ceiling and insulate, could I put unfaced R-30 insulation between the ceiling joists and then radiant barriers to the underside of the roof sheathing? Should I used Kraft-faced insulation with the facing against the ceiling?

My garage is square so I have four roof sides coming to a peak in the center.
There is no ridge vent because there is no ridge. How useful would a turbine be in keeping the attic and the garage cooler compared to radiant barriers?

I have posted a lot of questions in the few weeks since I discovered this forum and I sincerely appreciate the time that experienced members have taken to answer them.