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Trying To Insulate Old House Roof

Name: Beth Clemensen  City: Scottville, MI

Question: My 2nd floor is under a sloping roof, with a small flat ceiling (and thus a small crawl space), sloping walls, 4 foot kneewalls. There was NO venting, and I added a full ridge roof vent, and soffit vents for every "stud bay". I added a layer of insulation over old grey insulation in attic crawl space. I found some bat insulation stapled to the ROOF side of the knee walls, and some layers of old newspapers stapled to the lath/plaster side of the knee wall. There is no insulation in slope / walls, and when contractor looked there is only about 4 inches of open space between the lath/plaster and the roof. I have HUGE ice dams every winter, especially over kitchen and bathroom (which are 1st floor). I believe warm air from 1st floor is rising, behind knee wall roof insulation, then hits sloped wall with no insulation and warms the roof. This melts snow, which trickles down and refreezes, etc., causing my ice dams. What do I do? Expecially with sloped wall? I think I'm going to have to tear out the knee wall / roof side insulation. I could then insulate the knee wall floor and lath/plaster wall ... insulate the warm walls, leaving roof cold. Then what? Should I close off the air space at the top of the knee wall? The start of the narrow slope? Then put in a mushroom roof vent, so cold air from soffits can exit out from knee wall space? Another web site suggested pouring styrofoam beads into the narrow sloped / wall. They were uncertain if I would need a barrier to keep beads away from roof. Also uncertain whether 4 inches of beads would actually be a worthwhile insulation. Another site suggested cutting stiff foam boards, to fit each stud bay, and sliding them into slope. Another (and probably the best) suggestion was to do injected foam into slope, which would close off all air movement, removing moisture problem, but no one within 150 miles (!) does that. (They do spray nozzle on open construction, but not injection in existing walls.) P.S. Don't criticize the original builder ... it was my Grandfather, a master carpenter in the 1920's. When he built it, the upstairs had NO heat. In the 1940's he cut a hole in the floor of one bedroom... when my Mom was pregnant with my older sister. Oh yeah, the upstairs now has hot water baseboard heat.