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Old 07-04-2014, 06:06 AM   #1
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Taping multiple layers of foam insulation


I am finishing my basement. I already had 1" insulation over concrete when I purchased the house. I built my non load bearing exterior walls with 2x2 plates top and bottom and using 2x4's turned sideways creating 1.5" thick walls.
I got some Owens Corning insulation which states it is 7.5 r value. Not sure if that is total or per inch. If it total that I need to return it for a higher to meet code here.

However I was wondering about taping. Currently the 1" is not taped. I was wandering if both 1" and 1.5" should be taped. Or just 1 layer? My concern is with moisture. Anyone have an answer to that? Or my question about the r-value of that insulation?

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Old 07-04-2014, 08:32 AM   #2
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Taping multiple layers of foam insulation


In general, the r value stamped on the product is the total r value, no need to do any cyphering to figure it out. SOUNDS like XPS foam which has the lowest r value per inch of the commonly used foam sheets. Ron

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Old 07-05-2014, 01:21 PM   #3
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Taping multiple layers of foam insulation


Quote:
Originally Posted by ront02769
In general, the r value stamped on the product is the total r value, no need to do any cyphering to figure it out. SOUNDS like XPS foam which has the lowest r value per inch of the commonly used foam sheets. Ron
XPS is not the lowest. EPS is lower and ISO is higher.

The OC Foamular is typically an XPS product.
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Old 07-06-2014, 02:48 AM   #4
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Taping multiple layers of foam insulation


Yeah I'll be returning the Owens Corning xps for some ISO.

Now what about the tape? Should I tape the 1" foam against concrete? The ISO layer on top? Neither? Both?
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Old 07-06-2014, 10:03 PM   #5
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Taping multiple layers of foam insulation


If I don't tape anything it seems like it would be drafty. But taping worries me about moisture
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Old 07-07-2014, 11:14 AM   #6
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Taping multiple layers of foam insulation


Condensation is the result of water vapor produced by people in the home.
People cooking, washing, drying, breathing, sweating...and animals.
Water vapor is programmed by nature to move to cold surfaces (surfaces below dew point) to turn into condensation.
If your insulation is thick enough to hold the room side surface above dew point then any tape you fit on it will keep dry.
Just make sure that all holes, gaps and cracks are tight, that is to say water vapor proof. The best thing to do, is to cover the whole wall surface with plastic sheet, if you don't then water vapor will find its way through the insulation cracks and will condense on the cold wall behind it.
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Old 07-10-2014, 08:53 AM   #7
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Taping multiple layers of foam insulation


Soooo seal up everything completely?
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Old 07-10-2014, 09:25 AM   #8
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Taping multiple layers of foam insulation


Its simple really, by presenting a warm surface to water vapor (that is to say one above dew point) the water vapor is held in the air (or goes somewhere else to condense usually the cold surface of a window) by covering the insulation with a plastic sheet, this removes all the problems caused by cracks in the insulation.
Look at it this way.....things can be made air tight reasonably easily, but the molecules of water vapor are so small that they can live and exist between the molecules of air.
Make sure you glue/seal any gaps between plastic sheets and round the edges of plastic sheets.
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Old 07-10-2014, 09:32 AM   #9
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Taping multiple layers of foam insulation


Perry is all over it.

The benefit to staggering the seams and offsetting them is to get more air barrier layers and more foolproof sealing.

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