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Slate Affair Inc.
Intermediate Member
Username: Slate_man

Post Number: 40
Registered: 01-2007
Posted on Sunday, April 08, 2007 - 07:03 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Well I would frame in inside walls 2x6 and fill then with the insulation. This would leave all of the old roof system to vent. If you don't you may trap that moisture. If it out of the question to do so, you may need to take the plaster of and install a proper vent in that space.
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Michael Udris
New member
Username: Udris

Post Number: 1
Registered: 04-2007
Posted on Thursday, April 05, 2007 - 03:14 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

I have searched extensively but have been unable to find an answer. I have an 1889 second empire victorian with a full 3rd floor slate mansard. There is currently no insulation in the attic but as I am rewiring and plumbing the 3rd floor it leaves me room to install all my mechanicals before I get around to insulating in the fall. I plan to blow in insulation and am wondering about ventialtion/condensation issues. Ideally, when I blow in the cellulose, I want to blow it down the mansard exterior wall cavities as well. I can look straight down these cavities with a flashlight (plaster and lath on the inside face, wood plank sheating on the outside face beneath the slate). Because I am not gutting the 3rd floor plaster walls, there is no option to install a moisture barrier. As far as I can tell the only ventilation at this part of the house comes in a few feet above the attic floor, where the hipped roof meets the top of the mansard, a gap that runs the perimeter of the house. I have also installed some vents at the top of the hip. My questions are as follows:
1. If I blow insulation down those wall cavities do I have to worry about condensation? I thought I read somewhere that I could be trapping moisture that would rot out the mansard sheathing. Others seem to say this isn't a concern so i'm at a loss as to what to do.

2. What are my best ventilation options for the attic? I would like to install a whole house fan, but as this attic has no soffit vents nor gables through which I can punch out vents, i'm left with opening more holes in the roof. With a ~9000 CFM fan (to vent 3200 sq. ft. of living space) that's going to mean a lot of square feet of ventilation. Are there other devices like spiral vents or solar ventialtors that would make this work better? Thanks for your input.

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