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Old 05-03-2014, 10:56 AM   #1
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Insulating around windows


I want to use foam insulation around windows. Presently there is fiberglass. Can I foam over fiberglass? Is there any issue with moisture if I leave fiberglass? Thank you Tim

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Old 05-03-2014, 02:09 PM   #2
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Insulating around windows


Just use the DAP foam in the can. Cleans up with water. Fiberglass is not airtight. It will breathe just like we breathe. Mainly helps to keep dirt out of the house.

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Old 05-09-2014, 01:48 PM   #3
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Insulating around windows


No issue. Just push the fiberglass in so that you have adequate space for your foam.
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Old 05-09-2014, 03:05 PM   #4
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Insulating around windows


Compressed fiberglass has no insulation value. Remove it and use low expanding foam.
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Old 05-09-2014, 05:00 PM   #5
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Insulating around windows


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Originally Posted by joecaption View Post
Compressed fiberglass has no insulation value. Remove it and use low expanding foam.
You leave it in to act like filler foam. That way you are not using a whole can of foam to do two windows.

You want to just leave it in there. I did that with mine, when I went around and filled around the perimeters with the DAP foam in the can. Helped a lot doing it that way.
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Old 05-09-2014, 05:10 PM   #6
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Insulating around windows


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Compressed fiberglass has no insulation value. Remove it and use low expanding foam.
Youcan use the foam to seal gaps/cracks... but as Joe says, you don't want to pack the insulation, .... you actually loose insulation value if you do.....

Sometimes the small gaps between rough frame and window frame have been jam packed with insulation (probably by well intentioned but not well informed tradesmen).... I think that would be great to pull out and fill with the non-expanding foam.
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Old 05-10-2014, 07:22 PM   #7
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Insulating around windows


R-13 insulation is just R-30, compressed.
"

From pp.41; http://www.huduser.org/Publications/pdf/walls.pdf

The density increases as you compress it, losing total R-value BUT gaining density (R-value) per inch; means better insulation. It is far from worthless- with no insulating value: think FG board insulation (on HVAC ducts);
"Common Name(s): Rigid fiberglass
R-value per Inch: 4.4
Strengths or Best Use: easy DIY installation, air can go around but not through this insulation, used for roof insulation (commercial) and foundation insulation, used in narrow cavities, not susceptible to moisture damage, naturally fire resistant (needs no additional chemicals)
Weaknesses: expensive, not available everywhere" From; http://www.insulation-guide.com/insulation-types.html

So as you compress fiberglass, it increases the density for better air stoppage/insulating qualities, but will never equal foam for air sealing; read a few pages-- http://books.google.com/books?id=a29...(1995)&f=false

Most people are aware that FG losses R-value when compressed, but fail to realize it gains R-value per inch of material installed. http://www.greenbuildingadvisor.com/...fiberglass.JPG

Just push it in more for room for the foam, you are not after the minimal R-value gains in the window/door perimeter (compared to over-all wall/ceiling/floor) but the air-stopping value of foam.

Gary
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Old 05-11-2014, 10:41 AM   #8
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Insulating around windows


It is exponentially more important to get the gap sealed than it is to insulate.

Get a good window and door foam and it will be close to an R-6 per inch. That small gap and compressed FG is not going to make the insulation schedule a poor performer.

Pushing the FG to the outside edge will also keep the foam from possibly expanding out and interfering with the siding if there is no housewrap.

The wall is already only an R-4 at best at that location (i.e. stud wall), compressed FG and foam are still far superior and I think there is less fudge potential if you leave the FG in there (i.e. as mentioned above).
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Old 05-11-2014, 07:55 PM   #9
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Insulating around windows


Didn't read the whole thing. Sorry. But someone suggested packing the fiberglass in...and that can be a BAD idea toack too tightly because.....you can actually push the sides out of the window out of rack. Ron
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Old 05-12-2014, 09:06 AM   #10
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Insulating around windows


well stated above... you are not looking for r-factor in a 1/8-1/4" gap around the perimeter of a window, you want a seal there. Push the fiberglass in an it acts as a backer rod for your foam. Do be careful though as ron stated not to over do it so far as to bow the side jambs in... If you want to pull the fg out, thats okay too, not a huge difference either way.

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