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Old 04-10-2008, 09:01 AM   #1
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Why are there so many different insulation recommendations?


I've been using the information on this board to determine whether we should insulate our basement. Everytime I read a different basement post there is different insulation recommendation. Some say vapor barrier some say no, some say insulate all, some say part. Why so much variation? i realize climate has some effect but aren't there any basement insulation absolutes?

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Old 04-10-2008, 08:06 PM   #2
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Why are there so many different insulation recommendations?


You need a vapor barrier in a basement. Chances are you already have one as is the basement is waterproofed and not leaking, the waterproofing is acting as a vapor barrier. I don't know of any below grade waterproofings that are vapor permeable. If you have some moisture problems on the inside thats a whole different animal. If there is moisture you either have to excavate and repair the exterior waterproofing or use a quality blind side waterproofing. The placement of the vapor barrier is what is usually the variable. But basements are somewhat easier as the temp of the ground is cool year round. So you have a cool damp wall and a heated interior space in the winter time. Biggest thing you want to avoid is condensation. That will happen when warm moist air contacts a cool surface. In basement you will almost always have a "heating climate" this means your interior air will be warm and your wall will be cold. In this case you are better off trying to prevent any moisture from the warm interior side from contacting the cold exterior wall which will cause condensation. For that reason I would put a vapor barrier behind the gypsum/sheet rock. Any moisture which exits from the exterior wall will come in contact with warm air which is not a problem

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Old 04-10-2008, 09:34 PM   #3
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Why are there so many different insulation recommendations?


I found some pretty good info here on basement insulation,
http://www.eere.energy.gov/buildings/building_america/
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Old 04-10-2008, 10:09 PM   #4
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Why are there so many different insulation recommendations?


i disagree with the vapor barrier, i have posted other replys and the vapor barrier will collect moisture and trap it . if you do insist on installing vapor barrier make sure it is a tyvek, or certainteed has a breathable, one way vapor barrier made for interiors.
a plastic vapor barrier stop water vapors as the pass from interior to exterior.
if you have a concete wall with tar or water proofong on outside (this is a vapor barrier) and you build a 2x4 wall , insulte , install plastic vapor barrieer, then drywall. the dew point on that system you just created is located in the middle of the 2x4 wall ( where hot and cold meet ) the condensation created from that is now trapped in between two layers on vapor barrieer and has no where to go . very touch subject your deling with. good luck.
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Old 04-11-2008, 06:06 AM   #5
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Why are there so many different insulation recommendations?


Tyvek, or other housewrap products, does not qualify as a vapor barrier in any jurisdiction. Its designed as an air barrier.

The local building department decides how you should be contructing basement walls in your area. Contact them first before deciding on a method.

If the basement walls are constructed properly and sealed properly, there will be no moisture issues. This means carrying the insulation up into the joist spaces,lots of tape, sill gasket, VB, AB, acoustical sealant, moisture proof electrical and a dry basement to begin with.
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Old 04-11-2008, 06:32 AM   #6
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Why are there so many different insulation recommendations?


in most basements you have a problem with the moisture that is in every house. im not referring to moisture coming in from outside.that moisture will try to move to the outdside and a plastic barrier as so many people use is not a good idea. as far a the building dept go es , the only recommendation they will have is the inspectors personal belief. a lot of inspectors do not have the proper traing, hand on etcthat the should
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Old 04-11-2008, 03:58 PM   #7
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Why are there so many different insulation recommendations?


I live in GA. I contacted a building inspector in our county who said frame, use r-13, then sheetrock. We already used waterproof paint on the concrete prior to talking to him but he said it wasn't necessary. He said the vapor barrier was not neccesary and that the Kraft paper on the insulation would help prevent moisture damage. I'd be willing to bet I could call someone else and get a different opinion. We spoke to 3-4 others who are in the construction industry and everyone has told us something slightly different. It's just frustrating because we are DIYers who are trying to figure out what the "right" thing to do is. He also referred us to the IRC manual. Evidently that is where their codes come from.
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Old 04-11-2008, 05:12 PM   #8
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Why are there so many different insulation recommendations?


every house is different, things like type of furnace , air conditioning, climate , soil conditions,etc all come into play. and many people only tell what they have done. and sometimes you dont know, what you dont know!


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Old 04-11-2008, 07:38 PM   #9
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Why are there so many different insulation recommendations?


Just an FYI Kraft paper is not a true vapor barrier. A vapor barrier has a permeance of less than one with most being 0.01. Kraft paper is more like a felt paper. Its permeance increases with saturation. If I remember it rises from about a 1 (dry) to around 10. Felt is 5 dry 15 wet. Europe is experimenting with smart vapor barriers that increase in permeance as moisture rises

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