Insulation, Radiant and Vapor Barriers - Insulating wall AFTER sheetrock is up?

I have a cape and plan on insulating the knee walls for the two upstairs rooms. Right now, there is no insulation on the backs of these walls and the crawl space behind them gets quite cold. After reading about 50 articles about the proper way to add insulation, I am more confused/concerned than ever. I understand that the vapor / paper side of the insulation roll should face the room and be stapled to the 2x4s. How can I do this since I am adding the insulation from the back of the wall and not from the front? Should I just push the insulation in there and call it a day? I read something that said that the paper side is flamable so it should make a good seal to the sheetrock so there isn't air space for fire to spread. How can I make a good seal if I am pushing it in from the back and can't staple it?

Please... Someone help me!! What do I do in this situation?

Thanks in advance!
:confused:

use unfaced insulation

use unfaced insulation

Shouldn't a vapor barrier be used when insulating between a warm room and a cold crawl space? I would rather have a higher heating bill than mold spores in the bedrooms.

Paper is not a vapor barrier

I am confused. The rolls of Owens Corning insultation have a paper backing (with something inside possibly) and the package says "Faced with Vapor Barrier". I am assuming the package is correct.

Here, this type of insulation is no longer approved for use.
The paper backing is indeed a vapor barrier but when you staple the edge of the paper to the stud and press the drywall against it you are not getting a proper seal.
I suppose if you were to run a bead of acoustic sealant on the studs and were to be able to extend and seal the backing to the top and bottom plate it would then retard moisture.
However this is not practical and is why we do not use this product in our climate.

I would check on the codes where you are but in my mind the only way to have an impenetrable barrier is to use a continuous layer of poly that is sealed on the edges.
And, on the warm side of course.

Excellent information Greg. Thank you! I am learning (little by little) :D. So, what would you do in this type of situation where the sheetrock is already in place? Would you, as suggested by Airman, use an unfaced insulation and just push it in between the studs or would that put me at risk of a moisture issue?

Also, are there any options other than fiberglass that would make sense in this type of situation? Should I drop the fiberglass idea and spend the money on the foamboard kind of insulation?

How ever you do it you will need a continuous layer of poly between the insulation and the cold wall.
It would not make much difference using foamboard, which is not as good as fibreglass in my mind, mainly because it will not fit out of kilter studs without carefull trimming.
In some retrofits you are able to access the inside wall to place the poly but in some you must remove the sheetrock and work from the outside to the inside.

The risk of moisture damage to your home is increased as the outside temperature becomes lower.
Here with outdoor normal temps in the 0 degF range and -30 degF and lower not uncommon, the vapor barrier methods I describe are a requirement.

Can't really offer any easy answers, especially without being there.
Perhaps someone having experience with your weather will chime in.

[A free return airline ticket and a place to stay might get you some better advice. :D ]

How about $20 and a bus pass? :D

In all seriousness, thank you for your help. Unfortunately, I feel like I might need to hire a professional to do something that seems like it should be such an easy thing. I can't believe I am the only one in the world that needs to install insulation to a wall from the back side (after the sheetrock is already up) but it seems that instructions for doing so are hard to come by. :(

Instead of putting insulation between the studs, you can put rigid extruded polystyrene over the wall. You can put it over existing sheet rock or you can sheet rock over it. It can function as a vapor barrier. You will need longer screws and possibly electrical box extensions if the area is wired.

Dick