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Insulating attic dormer kneewall spaces

Posted by paul on February 10th, 2001 02:40 PM

I apologize for my lengthy message. For 10 years, I live in a vinyl-sided house with a full wraparound porch with continuous venting on the eaves. My house has six dormers on the second floor. Because of this, there are 12 openings into the heated living space from the unheated areas on either side of each dormer. On the outside walls of the living space there is 3 " R-13 Certainteed insulation installed with the paper side against the drywall. I have added blue styrofoam board over the doors (12 of them!) glued to the non-living space side. There is no other insulation other than that in the attic which is yellow with the paper side against the drywall. I don't know the R-value; I can't tell without ripping up a piece but it is at least as thick as the rafters. It was stuffed very tightly into the openings where the rafters met the top of the walls. To allow the air to drift up from the eaves to the attic I installed styrofoam channels between each rafter between the insulation and the roof. I also have installed a continuous ridge vent from one end of the roof to the other and two powered attic vent fans. We have relatively new heating/AC systems (4 yrs old) Inside each of the dormer spaces is the 1x6 plank subflooring covering the first floor ceiling. The outer walls have no insulation. In fact you can look down onto the ceiling of the porch and you can see daylight in the cracks in the fiberboard sheathing and vinyl siding. In some of the dormer spaces, the previous owner had installed pink R-13 insulation between the roof rafters with the insulation directly against the roof sheathing and the paper side facing the room. On the advice of a friend, I removed this. In the winter, it is much colder in these areas than the attic and in the summer it is much hotter than the attic. Can I put some type of insulation over the outer walls and continue my foam vent channels down the roof rafters to where they meet the rafters for the porch? That would stop the cold/heat entering these areas but I'm concerned about trapping moisture; isn't the paper backing already against the drywall wall acting as a moisture barrier? Someone suggested using a double foil-sided foam insulation board over the in-place insulation and not worrying about the actual knee wall space. Please, I would appreciate any advice. It's expensive to both heat and cool this area and I would like to address this problem while it's not too hot to get in there to work. Again, I'm very sorry for the length of my posting.

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