How to properly vent a modfied gambrel roof?
Hi,
My family and I purchased a 2 story modified Gambrel style home 5 years ago. By modified, I mean that the vertical roof sides go all the way to the foundation. So we have sloped interior walls upstairs and downstairs.
I live in Zone 6A. We all know what this winter has been like. Ive got an ice dam at the top of the vertical roof on both sides. There has been a fairly large crack in the downstairs sheetrock since moving in, just haven’t started our interior renovations yet. Last week that crack started falling apart and is wet. Further inspection shows wet sheetrock/carpet upstairs, attic frost/moisture in attic, and a frozen patch on the outside of the vertical roof matching the crack.
I know I need to fix the air leak to the attic (the crack). And I need to reinsulate this area at a minimum due to the moisture.
What Im not sure about is how to permanently fix the ventilation problem. There are no soffit vents at the bottom of the vertical roof or at the transition to the typical sloped roof. There are gable vents in the attic, no ridge vent.
I had a couple contractors out to look at this weekend and they are suggesting a complete sheetrock removal, add soffit vents, install baffling for the entire vertical wall, reinsulate, re-sheetrock. They aren’t sure how to add soffit vents to the vertical roof, as there is no overhang, and they will get plugged with snow on occasion since the vertical roof starts 1.5-2′ above grade.
Ive got other people telling me that what they plan to do will create a bad fire hazard, by venting the entire wall with no fire blocks. I think I agree. Ive also had suggestions on using a spray insulation in the vertical roofs to stop all air flow.
How should this be done properly? We may try to tie in an addition to this “remodel”, so there will be a chance to properly fix that side of the house how we choose. But the side with the current issue is likely to remain the way it is.
thank you
Charlie
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Charlie,
You can choose to build either a ventilated assembly or an unventilated assembly. Either approach can work, although the vented assembly needs clear channels above the insulation layer, from the "soffit" (some type of screening just a few feet above grade) all the way to the attic or ridge. If (from your inspection and knowledge of the roof geometry) you feel that creating these ventilation channels is impossible, you should choose an unvented assembly.
In my opinion, this is a roof, not a wall. If you have ice dams, you want to create an unvented roof assembly with a minimum R-value of R-49. This article will tell you how to do it: How to Build an Insulated Cathedral Ceiling.
Thank you for the response. I am getting conflicting opinions on where to spray foam.
For reference, the vertical roof/walls are balloon framed from the 1st floor decking to the attic, closed on the bottom because they sit on the decking.
My thought was to foam the vertical roof/wall up to attic, blow in insulation in the attic and leave gables open. But Im getting one opinion saying to foam the attic roof, close the gables and put fiberglass back in the vertical roof/wall.
We've come down quite a bit in the scale of what we plan to do. And just want to get the moisture damage fixed and try to permanently fix this one side of the house by insulating properly in the process. Do you see any issues having one side (the sunnier side) left as-is with fiberglass and closing in the other side with foam? The other side isn't currently having any issues and I think we will wait until we are forced to do something with the roof before getting deeper than we need to now. This is assuming that my assumption of foaming the wall is correct.
thanks again
Charlie