# Where to apply vapor barrier(s) for wall insulation



## patented (Aug 1, 2012)

I am getting ready to insulate a wall of my 100yr old home as part of my kitchen remodel. The wall has been torn down to the studs, exposing the exterior sheathing. The wall is made from 2x4 studs.

As of right now, my wall has (from outside to inside) hardiboard siding--1x6 sheathing--old tar paper (dryed out and full of holes).

When I put in the new insulation, should I first apply new tar paper to the sheathing before I put in new insulation? Or will adding a vapor barrier to the sheathing cause problems?

I live in the St. Louis area (hot/humid summers and relatively cold winters).

I plan on using fiberglass batt insulation with the kraft paper backing.

Thanks.


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## tvanharp (Mar 10, 2011)

This sounds like a perfect spot for spray foam. Seals all the cracks and holes. Then insulate and vapor barrier over that.
Only bad part is that spray foam is expensive. Also i prefer to use poly instead of or in addition to the kraft backed bats. The purpose of vapor barrier is to keep moisture out of your walls, i dont see how paper can do that, just my opinion.


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## joecaption (Nov 30, 2011)

Do you already have fire blocking at the bottom and tops of the walls?


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## Gary in WA (Mar 11, 2009)

No Class 1 for your location: http://www.buildingscience.com/docu...heet-310-vapor-control-layer-recommendations/

Gary


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## jklingel (Dec 21, 2008)

Fiberglass batts are the worst batt insulation there is, and no real fun to install. Try to get rock wool (Roxul), cellulose, or cotton (both treated w/ borates). As for the vapor barrier, apply it to the waste basket, no the walls. Air seal instead.


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## Nailbags (Feb 1, 2012)

tvanharp said:


> This sounds like a perfect spot for spray foam. Seals all the cracks and holes. Then insulate and vapor barrier over that.
> Only bad part is that spray foam is expensive. Also i prefer to use poly instead of or in addition to the kraft backed bats. The purpose of vapor barrier is to keep moisture out of your walls, i dont see how paper can do that, just my opinion.


Every one has their opinion on insulation from what you said your doing having the Kraft paper on the batts face it to the living side of your home all is good. So people will say batts are the worst etc just a FYI on that If was so bad people would not buy it or it would also not meet code. it works it is green. Just know your doing ok.


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## jklingel (Dec 21, 2008)

Nailbags said:


> ...So people will say batts are the worst etc just a FYI on that If was so bad people would not buy it or it would also not meet code. it works it is green. Just know your doing ok.


 There is no question about FG batts being the worst batt insulation on Earth. It is not an opinion; it is science. They do not have the density that other materials do, so they leak air internally; convective loops. That reduces their published R value. They can not be installed perfectly, and small gaps add up to serious heat loss. They are not an extremely uniform material, either; none that I have ever seen or heard of talking with others who use them. That said, just because they are the worst does not mean they are worthless. As I've said here many times, they are OK, but not great. I have 13" of FG in my walls (two, 2x4 walls, with a layer of 5.5" stacked between like hay bales) and they are doing OK; my fuel bills are far lower than many homes here. That said, better batts would be doing better. The reason people buy them is because they are ubiquitous and everyone is familiar with them; they are heavily advertised and they are the insulation we all grew up with. Too, how many people study building science, or GAFRA to do so? Few. And FG is hardly "green" like cellulose is; there is, if I recall the pecking order correctly, a lot of embodied energy in glass threads. Meeting code is nothing to brag about; codes are minimums. In summary, use FG batts if you want to, just know they are only OK.


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