Insulation, Radiant and Vapor Barriers - Faced batts & Plastic??
Doityourself.com community forum was created to provide answers to all questions related to home improvement and home repair. Doityourself community can help you find information about how-to topics on small fixes to large remodeling projects. With comprehensive how-to content and expertly moderated community forums DoItYourself.com makes it easy to tackle even the most complex home improvement projects.View Full Version : Faced batts & Plastic??
kathie659
12-02-06, 12:00 PM
I just ripped all the exterior walls in a rental unit. After electrician is done, I'll be insulating. I have R-13 faced insulation (the 3.5 inch R-15 wasn't available at the time)....
Is there any benefit to installing plastic film between the paper face and sheetrock? I've been in reno's that have the film and was shown the difference in air infiltration into the home on walls with and without the film (both cases the sheetrock had not yet been installed)
My concern would be moisture build up and possibly mold growth. I do like the idea of less air infiltration. (BTW @ this remodel they had installed 2x4
@ floor and ceiling to reduce draft, but there was still a lot of air flow in wall w/no film)
So which is it plastic or no plastic (I'm in NE Pennsylvania)
Is there any benefit to installing plastic film between the paper face and sheetrock? I've been in reno's that have the film and was shown the difference in air infiltration into the home on walls with and without the film (both cases the sheetrock had not yet been installed)
My concern would be moisture build up and possibly mold growth. I do like the idea of less air infiltration. (BTW @ this remodel they had installed 2x4
@ floor and ceiling to reduce draft, but there was still a lot of air flow in wall w/no film)
So which is it plastic or no plastic (I'm in NE Pennsylvania)
resercon
12-06-06, 09:53 PM
Yes you can install the plastic film (sheeting) over the faced insulation. The plastic sheeting will act as an air barrier and the faced insulation will be your vapor barrier. The reason why you can in this situation has to deal with Psychrometrics. This explains how moisture behaves at different temperatures. If you need further explanation, please feel free to ask.
kathie659
12-07-06, 06:12 AM
Psychrometrics (!!!) I've never heard the word. I looked it up and gather it pertains tothe effects of air flow on water vapor??
If you can provide a simple explanation as to why the plastic works over faced batts w/o mold concerns I'd certainly appreciate it.
Kathy
If you can provide a simple explanation as to why the plastic works over faced batts w/o mold concerns I'd certainly appreciate it.
Kathy
resercon
12-07-06, 07:06 PM
The reason why you can install the plastic film directly over the faced insulation has to do with Relative Humidity (RH%). This indicates the ability of an object to hold moisture. At 100% RH the object can no longer absorb moisture and condensation forms. The reason why they call it Relative is because the ability of an object like air to hold moisture is influenced by the temperature of that object.
To illustrate this is when I was young, I was fond of blowing up a balloon and then placing it in a freezer. A short time afterwards I would remove the balloon from the freezer and I noticed the balloon had reduced in size. Leaving the balloon out until it reached room temperature, I noticed that the balloon still did not reach the same size as it was before I put it in the freezer. After letting all the air out of the balloon I found moisture inside the balloon.
When I was young there was no such thing as a microwave oven. But if there was I could put the balloon into the microwave oven and heat the air inside the balloon until the balloon obtained the same size it was before I put it into the freezer. If I were to let the air out of the balloon at that point, we would not find any moisture or very little.
What this illustrates is how moisture behaves within objects at different temperatures. This applies to all objects, regardless if it is wood, sheet rock, insulation, etc. In fact most materials must maintain a certain amount of moisture in order to remain stable. In other words, too much or too little moisture the material destabilizes. An example of this is dry rot with wood.
Mold and mildew cannot occur without the presence of moisture. Since the vapor barrier (faced insulation) and plastic film will be installed on the warm side (facing the interior of the house) these two objects will be at or very near the temperature of the interior of the house and condensation is highly unlikely to occur.
To illustrate this is when I was young, I was fond of blowing up a balloon and then placing it in a freezer. A short time afterwards I would remove the balloon from the freezer and I noticed the balloon had reduced in size. Leaving the balloon out until it reached room temperature, I noticed that the balloon still did not reach the same size as it was before I put it in the freezer. After letting all the air out of the balloon I found moisture inside the balloon.
When I was young there was no such thing as a microwave oven. But if there was I could put the balloon into the microwave oven and heat the air inside the balloon until the balloon obtained the same size it was before I put it into the freezer. If I were to let the air out of the balloon at that point, we would not find any moisture or very little.
What this illustrates is how moisture behaves within objects at different temperatures. This applies to all objects, regardless if it is wood, sheet rock, insulation, etc. In fact most materials must maintain a certain amount of moisture in order to remain stable. In other words, too much or too little moisture the material destabilizes. An example of this is dry rot with wood.
Mold and mildew cannot occur without the presence of moisture. Since the vapor barrier (faced insulation) and plastic film will be installed on the warm side (facing the interior of the house) these two objects will be at or very near the temperature of the interior of the house and condensation is highly unlikely to occur.