How to build soffits to minimize ice dams

Umby

I have an L-shaped 1951 ranch with only one soffit on the east side of the house in S.E. Michigan. The back of the house (west), which is newer, has no soffits at all on the 3 sides where the gutters are. I have 3 fairly usless gable vents (two ridges) and about 8 can vents. I have winter ice dams on the north and south sides of the new section. I used to have them on the east section until I rebuilt the existing overhang and put in continuos soffit vents. I have excessive overheating in the attic in the summer. I would like to build out overhangs on the three sections of roof, put continuos soffit vents in them, remove the can vents, and cut in ridge vents. Any tips or sites for me to visit before I start this project would be greatly appreciated. Also is there a ratio of soffit square area to vent square area that I should be aware of? Thanks in advance for any help!

pipeguy

Attic ventilation techniques and methods have received considerable coverage here. Enter the keyword 'ventilation' in the search function and I think you'll find some useful stuff.

Umby

Thanks pipeguy, that was helpful. I also found a small bit on how to build soffits, but it is a site for building an entire house. I need help on how to extend rafters, build soffits, and deal with siding, all on an existing house.
I guess it's really a framing question more than a roofing one. Any help here would be great.