radiant barrier?

[Dawgfan77]

Im ready to purchase my radiant/vapor barrier for my shop:
-55Wx34Dx13H (I know, odd size...)
-Not climate controlled
-Fans in summer, kerosene or wood stove heat in winter-part time only!
-probably not dry walled
-open rafter, steel truss building
-metal siding and roof
-In South Carolina
I'm not so worried about insulation factor, but I'd like to cut the summer heat, and definitely control condensation! I've read tons of threads, but the vapor/radiant barrier debate always seems to veer into an insulation debate,... which then usually ends in a spray-foam debate. Not in my price range!
And the other issue seems to be the difference in vapor barrier installation methods from northern states vs. southern states vs. Midwest, etc... people seem to think there is one general rule for everyone for how to install, when there really isn't.

I am looking at the same old double-bubble foil that all the builders use around here, and stumbled across this stuff.

http://www.ebay.com/itm/Radiant-Bar...ft-/182372092958?_trksid=p2385738.m2548.l4275

At 1/3 the cost of traditional double-bubble, I suspect it to be inferior, but how much? I could double layer it and still save money. My biggest concern is that its perforated.... I realize there is a difference between my vapor barrier and radiant barrier, but the radiant barrier will in fact effect my due-point, which effects condensation... correct? So I guess my questions are:
1) will the perforation of THIS product matter? seems counter-productive...
2) 9.6 perms for a perforated material?? That seem high., low...?

 

[Dawgfan77]

Anyone?

 

[tfinniii]

Where do you intend to use it,wall, ceiling? They do 2 different things. It depends if you need to stop air flow , vapor movement or radiant heat blockage.

 

[-Brent-]

I use Arma Foil and I feel like it works exceptionally. I used first on my east end-wall of my garage attic and noticed a difference immediately. I've used it in other spaces, since, and always with noticeable results. I provided a link but I have no affiliation with them. It's just a decent, easy to use product.

 

[rburke65]

Is that stuff a VAPOR barrier or a "radiant barrier" ? For what are you looking? Do you know of contractors using this product? Can't you buy it at your local materials building outlet? Why eBay? Is there an R value or rating? Just my thought.

 

[Dawgfan77]

Sorry if the question was a bit hazy, I was at work when I typed it.
I plan to use on roof and walls of my pole barn shop.
My primary goal is a vapor barrier to control condensation since this is a garage, not really trying to insulate a lot- just because of cost. My understanding is that the best way to control condensation is with a good radiant barrier, which I suppose is why the most highly recommended vapor barriers have the foil backing--radiant barrier.
The stuff I linked claims to be both, and even gives a Perm value of 9.6, which is a rating for vapor retardant I believe. It doesn't give a "R-value", but I wouldn't expect it to since that's an insulating rating.
What caused my doubt is the fact that its perforated... to me that screams "Not a vapor barrier"! But I could be wrong. Has anyone used a perforated vapor barrier? I don't know of any contractors who use it, nor have I seen it in any store. And as I mentioned, its 1/3 the price of typical foil backed vapor barrier I've found locally, which is why it caught my attention. Ill check out the Arma Foil, thanks

 

[Firebrick43]

Where (in the building envelope) are you planning on installing this??

i think your confused on condensation and it's causes. A vapor barrier should go under a slab to reduce moisture coming up from the ground. Radiant barriers are absolutely worthless here as their have no adjacent air space to reflect the heat back in.

A radiant barrier under the roof panels can help reflect some heat out and keeps condensation on the bottom of the roof from dripping but does nothing to keep condensation forming on massive objects below. A "vapor barrier" here is really not needed and if perforations were pin pricks I would say that better as it lets water evaporates instead of pool on the radiant barrier.

Insulation and some air flow is the only way to eliminate condensation. It slows down temp swings and allows time for the massive objects to come up to temp so they are not below the dew point of the warm moist air around them. Radiant barriers and vapor barriers mitigate to a degree but dollar for dollar cellulose insulation followed by fiberglass is going to give you the biggest bang for your buck.

Radiant barriers are hyped as miracle workers and they advertise physically(and scientifically) impossible feats to make a sell. The do help (if they have an adjacent airspace to reflect heat into) but are just part of a system.

 

[Marctrees]

Dawgfan - About the foil bubble stuff, so much conflicting info no matter how deep you search.

Regarding the vapor barrier question - Search and learn on which side of the insulation you need, depending on what part of country.

You are "hot humid"

Search Google keywords "hot humid vapor barrier"

After much study, we did perforated vinyl faced batts in our building, near Texas "hot humid" coast.

Read through link below to glean what applies to you -- Marc

http://www.garagejournal.com/forum/showthread.php?t=340314

 

[Dawgfan77]

Ok, maybe I'm confused, or not being specific enough, so Ill try to give more detail.
Yes there will be a moisture barrier under my slab, buts that's a separate issue and already settled through my concrete guy.
When I say "vapor barrier" I'm referring to the moisture barrier -roof and walls. Maybe those are 2 different terms, I don't know.
When you buy a radiant barrier product, its basically aluminum foil, right? And most of the vapor/moisture barrier products (and even some insulations) I see have the same aluminum foil type backing on them, right? This is essentially a radiant barrier applied to a moisture barrier in the same product, right? Maybe I shouldn't use the terms so loosely.

Specifically:
-I'm only referring to roof and walls.
-laid over purlins and wall girts before sheet metal is installed.
-Full length roof ridge vent
-full vented overhangs all the way around
-attic fan in rear gable end wall

I realize insulation is the best way to control condensation, but in my area, it doesn't seem to be a necessity. I have friends with the same style shop, without insulation, other than the double-bubble stuff, who have no condensation issues.
Obviously, its not as good as a full climate controlled building, but not as expensive either. Here in my area, the general practice for pole barn companies is to use the "Double-Bubble Foil" type insulation/moisture barrier/radiant barrier. I use that term loosely because depending on what company or contractor u talk to, they all refer to it as something different-ie...double bubble insulation, double bubble moisture barrier, etc... But regardless of what they call it, they all use the same material.
I do intend to insulate with rigid foam eventually, but slowly.

Maybe my confusion is here: my understanding from local contractors- the condensation issue most hard fought HERE....in THIS area,... is not the moisture coming from the ground, that's easy to control with a simple 8mil moisture barrier under the slab
The big issue is the condensation that forms under the metal roof from heat transfer... which is why they recommend at least the double-bubble type product,... if you're not going to insulate.
Is this incorrect??
It seems to be opposite for the colder climates, or at least different depending on your climate. I feel like people mistakenly assume its the same no matter your climate

 

[Dawgfan77]

Marctrees, thanks, reading it now

 

[Marctrees]

Slab and walls/ ceiling 2 totally unrelated separated issues.

6 mil, or 4 mil at least, 8 mil even better( not that the permeability is better, just cause harder to damage, but 6 mil usually MORE than good enough) under slab ideally, in ALL climates and Geo areas, a good idea.

Under slab, and walls/ ceiling,,,,,, two TOTALLY different issues., NO relation in any way.

Vapor barrier in walls/ ceiling, vapor barrier on INSIDE in northern states, on OUTSIDE in hot humid cooling states, and in between the two, possibly no vapor barrier need anywhere.

Do your due diligence googling as I gave you keywords.. Marc

 

[Marctrees]

and don't forget - if you weather rapidly changes, and your slab is relatively cold, no amount of poly under your slab will limit sweating of the slab, if exposed to hot humid air.

Just like your iced tea glass carried onto your screen porch.

Sweats like crazy, even though there is a barrier of glass, RIGHT ???

Condensation. Marc

 

[Marctrees]

DEFINATELY poly under your slab, but the building is seperate issue. Marc

 

[Firebrick43]

Ok, maybe I'm confused, or not being specific enough, so Ill try to give more detail.
Yes there will be a moisture barrier under my slab, buts that's a separate issue and already settled through my concrete guy.
When I say "vapor barrier" I'm referring to the moisture barrier -roof and walls. Maybe those are 2 different terms, I don't know.
When you buy a radiant barrier product, its basically aluminum foil, right? And most of the vapor/moisture barrier products (and even some insulations) I see have the same aluminum foil type backing on them, right? This is essentially a radiant barrier applied to a moisture barrier in the same product, right? Maybe I shouldn't use the terms so loosely.

Specifically:
-I'm only referring to roof and walls.
-laid over purlins and wall girts before sheet metal is installed.
-Full length roof ridge vent
-full vented overhangs all the way around
-attic fan in rear gable end wall

I realize insulation is the best way to control condensation, but in my area, it doesn't seem to be a necessity. I have friends with the same style shop, without insulation, other than the double-bubble stuff, who have no condensation issues.
Obviously, its not as good as a full climate controlled building, but not as expensive either. Here in my area, the general practice for pole barn companies is to use the "Double-Bubble Foil" type insulation/moisture barrier/radiant barrier. I use that term loosely because depending on what company or contractor u talk to, they all refer to it as something different-ie...double bubble insulation, double bubble moisture barrier, etc... But regardless of what they call it, they all use the same material.
I do intend to insulate with rigid foam eventually, but slowly.

Maybe my confusion is here: my understanding from local contractors- the condensation issue most hard fought HERE....in THIS area,... is not the moisture coming from the ground, that's easy to control with a simple 8mil moisture barrier under the slab
The big issue is the condensation that forms under the metal roof from heat transfer... which is why they recommend at least the double-bubble type product,... if you're not going to insulate.
Is this incorrect??
It seems to be opposite for the colder climates, or at least different depending on your climate. I feel like people mistakenly assume its the same no matter your climate

Part of the confusion is you keep referring to it as a vapor barrier when it's not. It's a "condensation blanket". They have some similar properties but are placed in different locations in the building envelope. Vapor barriers go directly against the insulation, where condensation blankets go against the metal sheathing.

Here in Indiana condensation from the steel roof is a very real problem just like South Carolina. But also the slab will sweat and all the massive objects such as cast iron machinery, will form condensate as well. It's worse in the spring and will do it most mornings in the spring and fall as there is low temps at night and quickly rising temps as the sun rises.

The condensation blankets stop the rain from the roof but not the machinery from sweating. Only good insulation will do that.

 

[kbs2244]

If you have examples of building that preform the way you want, why would you not build yours the same way as them?