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-   -   Can foil faced foamboard insulation be layered? (http://www.diychatroom.com/f19/can-foil-faced-foamboard-insulation-layered-54894/)

Spud 10-11-2009 02:47 AM

Can foil faced foamboard insulation be layered?
 
Dow Corning Super TUFF-R Polyisocyanurate insulation board is faced on both sides.

1 side is blue (don't know what the blue backing is called)
http://i42.photobucket.com/albums/e3...Insulation.jpg

The other side is foil faced (Aluminum foil I believe)
http://i42.photobucket.com/albums/e3...supertuffr.jpg

If I get the 1 inch board, can I layer 4 layers, one on top of another?

Reason I ask is because of the foil backing. The foil backing acts as a vapor barrier so would layering these boards trap moisture in the foam and between the multiple boards , not allowing moisture to escape?

BTW
Is this in the right sub forum or should it have gone in the General Forum.

Thanks

Just Bill 10-11-2009 07:38 AM

I don't think that is the right way to do it. You have two vapor barriers, which could trap moisture between them.

Spud 10-11-2009 06:48 PM

Quote:

Originally Posted by Just Bill (Post 339034)
I don't think that is the right way to do it. You have two vapor barriers, which could trap moisture between them.

Dow has insulation boards that have foil facing on both sides, so that would trap moisture in the sandwiched foam?

As far as trapping moisture goes, would these double foil facing boards be similar in effect to layering multiple boards with single sided foil facing?

Or would the problem for me be the space between boards trapping moisture? and this wouldn't be an issue for single boards with double sided foil facing.

Dow Corning Tuff-R has foil facing on both sides.
http://building.dow.com/na/en/produc...tion/tuffr.htm

Quote:

Versatile TUFF-Rô Insulation fits numerous residential insulation and sheathing requirements and can be applied to a variety of substrates. It features a high-performance polyisocyanurate foam core with radiant barrier-quality aluminum foil facers on both sides (one side reinforced).

Daniel Holzman 10-11-2009 08:17 PM

The standard reasons given to avoid trapping moisture in insulation is to :

1. Avoid damage to the insulation due to moisture (some types of insulation, like cellulose, are adversely affected by moisture)

2. Avoid reduction in insulation R value

3. Avoid damage to adjacent wood surfaces due to condensed moisture

I don't see trapping moisture inside the polyisocyanate as being much of a problem, since the material is not susceptible to moisture damage, the R value is only going to be minimally affected by moisture, and if the moisture stays between the foil barriers, you care not going to affect adjacent wood surfaces. If the system traps moisture against a wood surface, that is a different problem.

Spud 10-11-2009 08:27 PM

Quote:

Originally Posted by Daniel Holzman (Post 339318)

I don't see trapping moisture inside the polyisocyanate as being much of a problem, since the material is not susceptible to moisture damage, the R value is only going to be minimally affected by moisture, and if the moisture stays between the foil barriers, you care not going to affect adjacent wood surfaces. If the system traps moisture against a wood surface, that is a different problem.

Will moisture migrate to the sides where it will come into contact with the rafters?

The ideal solution would be to just buy 4 inch thick Polyiso foamboard but I am not aware of anyone who makes such a thing.

I see that residential Super Tuff-R max thickness available is 1" but Super Tuff-R Commerical comes in max thickness of 2". Why is 1" the max available for residential?


1" of residential Super Tuff-R residential has an R-Value of 6.5.
The 2" Commerical Super Tuff-R board is R-12, shouldn't it be R-13?
why the slight loss in R-Value?
Commerical Tuff-R 2" is R-13.

Why does commercial 2" Tuff-R have R-13 while commerical Super Tuff-R has R-12?

BimmerRacer 10-12-2009 08:27 AM

I emailed Dow several months ago about stacking 2" boards and they said that it was OK.

RegeSullivan 10-12-2009 11:43 AM

I am pretty certain it's not the foil giving the foam it's ability to stop vapor penetration. The foam itself is the closed cell type so this would be a vapor barrier even if the foil was not there. The foil is heat reflective and you would want this facing or the side where you want to keep the heat. Heat energy is somewhat like light when it comes to reflectivity, hence the reason for the foil. I can see no reason not to stack it as long as you could stacked it tightly. Alternating the foil facing sides should make it more effective, two facing in and two facing out. Staggering and taping the seams of each layer would also make it more effective than just stacking it.

Rege

NJ Brickie 10-12-2009 10:04 PM

Why not just buy some foam that has no foil face and just have your last layer with a foil face?

Spud 10-12-2009 10:30 PM

Quote:

Originally Posted by NJ Brickie (Post 339888)
Why not just buy some foam that has no foil face and just have your last layer with a foil face?

Haven't found any that has R-6.5 per inch or higher. The non faced foam (blue foam) has only R-5 per inch.

If I could find a foil faced foam baord that is 4 inches thick, or non faced foamboard that is R-6.5 or higher per inch.

HISI 09-30-2010 07:37 PM

Hisi
 
There are several manufacturers of high density EPS foam - (compressive strength of 35psi plus that have R5 per inch ).
Amvic Building System in Toronto Canada makes up to a 5" thick board foil face 2 sides that has an R factor of 25.
Not sure if this is available in the US or not yet .
HC

Tom Struble 09-30-2010 07:41 PM

if its a vapor barrier,hows the vapor going to get inbetween? i would offset the seams then tape them,like dow says it's ok


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