Doing half rubber half shingle roofing.?

I have a 1969 house and the back side of the roof has a very flat pitch. I talked to a roofer that did his mom's house up the street, which is the same style as mine, and did rubber roof on the backside where it is less then the 2 inch rise/ft for shingles. I later read more on rubber roofing and I know that the petrolium in the asphalt shingles would destroy the epmd rubber if they touched but is there a proper way to make a seam at the roof cap to go from rubber on the flat backside to the cap and have asphalt front side? The roof is leaking in several places and did a lot with one bad snow storm that caused ice damming on the flat side. I was told a rubber roof would pretty much solve that problem. I have vaulted exposed beam ceilings with no attic and no insulation cavity so heat loss is excessive. I have also been searching for solutions to increase the R value of the roof. Right now all thats there is the birch on the inside, 2 inch buffalo board, then the shingles.

Public Comments

1. you could frame up the roof deck with wood and insulate in between it with hi density foam for more r value, seen it done (on this old house for example, they did it on a barn conversion). you could just go with 3/4" pine and the same size foam board, or use 2X4's and double it. you could then lay your plywood and cover it with ice and water shield then just use regular shingles on the whole house. i'm doing something similar with the siding on my house, removing the siding, tyvek and foam, then building out the trim to match the new 'face'. cheaper than rewiring the entire house and insulating it, these days, had to reside it anyways. get price quotes for doing it both ways, good luck.
2. I prefer bitumen (modified) over rubber. You apply it with a torch and when it cools, it makes a hard durable roof covering that outlasts most other low-pitch roof coverings. It comes in a couple different colors too.
3. use galvanized steel sheet metal of decent grade. you can buy it in rolls from 6 inch to 24 inch widths. not very pretty but it will get the job done.
4. There are a couple options I can think of. First, consider a metal roof or aluminum shingles. If you use aluminum, it will actually reflect away most of the heat. They come in colors other than silver, so it doesn't have to be ugly. There is also a material called polystyrene that has an R 5, and is sometimes used under shingles. R 5 isn't much, but it's cheap and it's better than nothing. Your best option is probably to put insulation and/or radiant barrier in between the ceiling joists under the roof decking. Then you can cover it with sheet rock. The link I'm including has a diagram of this application.