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I’m in way northern Michigan and have been asked to address ice dams and water back-up on vaulted roof of two year old home. I’ve discovered that rafters are 2×10, packed with fiberglass, no venting or venting channels, ceiling is painted drywall, no poly vapor barrier, condensation is occurring on plywood sheathing within cavity, severe ice damming at eaves causes water to back-up into home interior. I’ve been following various threads on vaulted ceilings and is obvious many methods are used for insulation but geographic area is normally not mentioned. I keep returning to tried and true method for addressing moisture and ice dams: Remove existing drywall and insulation, install full length vent channels combined with ridge and soffit vents, re-install insulation and drywall with poly vapor barrier. I’d like to provide owner with couple of options for addressing both problems (ice dams & moisture in cavity). Past experience suggests that a “cold roof” (vent channel to remove moisture and heat loss) is necessary as I can’t get enough insulation in cavity to stop formation of ice dams but is also obvious there is much experience out there with vaulted roofs. Your comments will be appreciated.
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Randy, If you consider that a 2x10 rafter with fiberglass will maybe be R-27 and then subtract your rafters, it is no wonder there is heat loss. And like you say no cold roof further complicates the issue.
My suggestion would be to strip the roof, lay down sleepers ( 2x2 minimal) and new sheathing and then a new roof. Install ridge vent and eave vents and you have a pretty good cold roof.
Personally I would like to see more insulation in the roof as well, to bring it to a realistic R-50, but that would take considerable more design and work. Unless you used a new roofing that could utilize skip sheathing ( wood shingles or metal roofing ) you will still need to create a cold roof.
just some thoughts
walk good
david
*I have similar ice-damming problems. I have looked through several threads and found some good suggestions, but nothing that matches my situation that closely. I am in a one-year old house in eastern B.C., in the Canadian Rockies (cold climate with lots of snow). Vaulted ceilings, 6/12 pitch with 4/12 shed dormers (the ice damming seems most pronounced on the shed dormer roofs). Asphalt shingles over plywood sheathing, R-40 fiberglass ins. between TJI's, with average of 4 inches airspace between insulation and plywood sheathing. Continuous vented soffits and ridge vents. Ceilings are vaulted in both the 6/12 (17 feet) and 4/12 (12 feet - upstairs bedrooms) portions of the house. Interior finish ceiling is T&G pine over poly vapour barrier. Note: we use our wood stove quite a bit, we have a ceiling fan in the living-dining room but not in the upstairs bedrooms. It seems we have done all the standard "right" things for venting and insulation, and yet I still see ice damming in this first winter in the house. Any thoughts or suggestions? Any thoughts on ridge vents getting clogged up with snow?
*jmamalis:I also am in big snow country and have had many problems with ridge vents clogged and covered with snow. About 8 years ago I installed ridge vent on my own home when I re-roofed. The next winter I noticed that when snow covered vent the ice started building up at eaves (attic insulation about R40) - remove snow and ice buildup stopped. I wrote to Fine Homebuilding and response from pro agreed - covered ridge vents do not breathe thus heat build-up. I installed gable vents too - now don't have to climb to roof and clear ridge in winter. Randy
*David: Thanks for reply. I too feel cold roof is the answer where there is much snow. Seems that with other systems one must always assume a degree of snow melt and ice build-up as there will always be heat loss. Keep your powder dry. Randy
*jamalis, A nother common problem which I have noticed that can cause ice damming is solar heating of the roof during the day. Here in Montana, even when it is below zero, radiant heating can allow snow to mealt on exposed roof areas and form ice dams once it leaves the warm area or the sun drops. This is especially true around dormers and chimney protrusions. My house is a good example. A 10/12 pitch with metal roof. Skip sheathing and gable vents in a large attic area above 20" of blown-in cells. Everything should minimize ice damming and yet I can watch it develope especially at the dormers. All it takes is for the sun to warm up the roof and start snow melt which runs freely until it reachs a cold spot and freezes. Thus the ice dam starts. Not as bad as some houses using shingles but still a problem. Like when the dam breaks. Look out.walk gooddavid