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Is It OK To Use Kraft Paper Batts And
Plastic Sheeting As A Vapor Barrier?

Jon From Illinois wrote:

Hi,

My name is Jon. I have been searching the net for some answers to a couple of questions that I had about insulating my attached garage. I read all your info. on your site in the garage category. Here is what I have going on. I have a house that the garage has been built and attached after the house was built, so the attics do not connect. I recently decided that I would be nice to have a warm place to tinker in the winter time so I have started in on the project of insulating. So far I put R-13 craft faced in the walls then put a 6 mill plastic vapor over that, then sheeted over the top of all of it with 3/8 bc plywood. Now that the walls are all done I have started on the ceiling. My rafters are on 24'' centers and i got a good buy on some R-13 craft faced insulation 23'' wide. My intention is to do the ceiling the same as I did the walls with the insulation then the 6 mill plastic to keep down any wind that may find its way through the cracks then the plywood, I may at a later date blow more insulation on top of the roll-in to get more R-value. I live in west central IL in the country and have no building code out here as far as having to comply with anything. Does this process sound ok to you? Is there any thing that you would suggests to do different? Also will it condensate between the plastic and the wood and rot out the sheeting in the ceiling over time? Any help would be appreciated there's not many people that do insulation around here to ask.

Thanks

OK. You are installing R-13 kraft faced batts in the ceiling. The kraft paper acts as a vapor barrier and usually there is no need to add anything additional, such as the 6 mill plastic sheeting you're referring to.

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Remember, all vapor barriers need to be installed on the heated side of the joists towards the living space and will have the sheetrock attached to it. Never place a vapor barrier over the top of the insulation in the attic or you may encounter dry rot in the structural members of your ceiling.

I'm not sure in your description on how you want to install the plastic sheeting but if you have the kraft paper on one side of the fiberglass batt and plastic sheeting on the other it will cause major problems. If this is the case you will need to climb into the attic and remove the plastic sheeting immediately.

On another note you said you are installing R-13 in your attic. That's not much and you will still lose a substantial amount of heat. For your neck of the woods I would recommend bring it up to at least a R-38.

Good luck with your project and if you have any questions please just let me know.

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