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attic insulation and vapor barrier in addition

We are building an addition and were going to use blown in cellulose R49 to insulate the attic. It seems like, for living in Massachusetts, we should be using a vapor barrier? If that is the case, can we use faced fiberglass for the vapor barrier, then blow in cellulose to get the R value up to 49?


Re: attic insulation and vapor barrier in addition

Disclosure: I am a spray foam contractor in MA. I do a lot of work in the gas company rebate program. I spray the underside of the roof. All of the houses I work on have insulation in the ceiling. The problem is that porous insulations allow air to move through it, carrying heat with it. Air comes up through all the penetrations in the ceiling, like wires, plumbing and especially recesssed lights. In one house we compared gas bills and he used 30% less gas after insulating. If the picture attached, you can see that my customer still has snow on his roof. The snow has melted off his neighbor's roof due to heat escaping the houses.

It is especially important to spray (insulate) the underside of the roof if there is heating, cooling or duct work in the attic, because, otherwise, you are putting this equipment outdoors.

Technically, to answer your question, you should have a vapor barrier. But it isn't going to do much good. You could put vapor barrier paint on the ceiling instead. There are some details to get the cellulose right. I wouldn't use fiberglass for anything, especially in an attic. If you want to reach me: [email protected]

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