Replies

1. GBA Editor
   Martin Holladay | May 01, 2016 05:17pm | #1

   David,
   The best approach is certainly to add rigid foam insulation above the roof sheathing. In what sense is there no "room" there? Is there a zoning restriction on your building height?

   I don't recommend the cut-and-cobble approach (which you are suggesting) for unvented cathedral ceilings. Read this article to learn why: Cut-and-Cobble Insulation.

   The only approach I know of that will meet the criteria you list is to install spray foam insulation on the underside of the roof sheathing.

   Here is a link to an article that will guide you: Insulating Low-Slope Residential Roofs.

2. 
   coward13 | May 01, 2016 06:12pm | #2

   Adding insulation to the top would be an aesthetics issue. The added roof height would look odd from the front of the house ( dormer is in the back, centered across house. Its roof meets the gabled roof at the ridge). If I wedged it, I'd lose some of the little slope that I have on the dormer.

3. 
   coward13 | May 01, 2016 06:54pm | #3

   What about removing sheathing, then use spray foam from the top. A variant of cut a cobble -- rigid sheets between the rafters, inserted fairly tight, pushed down to form a cavity to spray closed cell foam from the top. Trim excess foam as needed before applying new sheathing. Spray foam adequate to eliminate cut and cobble sealing issues.

4. GBA Editor
   Martin Holladay | May 02, 2016 07:30am | #4

   David,
   If you rip some lumber on your table saw to create a piece with a triangular cross section, you can disguise the higher ridge from the from yard. What you want are a few long pieces with a cross section like the black triangle in the sketch below. (These pieces could be plywood-covered rigid foam if you want.) These pieces belong on the ridge sections that are not part of the dormer.

   Once these long rips are roofed, the higher ridge will be disguised from the front yard.

   Of course, from the back yard you will see vertical metal flashing at the right and left side of your ridge. Is that a problem? You decide.

   .

   
5. GBA Editor
   Martin Holladay | May 02, 2016 07:34am | #5

   David,
   Q. "What about removing sheathing, then use spray foam from the top?"

   A. That approach can work well, as long as you have a window of good weather.