Unfortunately if you already have an ice dam there isn’t much you can do while there is still snow on the roof. How do you prevent this from happening? Start by removing the snow from their roof as soon as they can. Once spring rolls around there is one big thing you can do insulate! I can’t stress that enough. The ice dam is cause by the heat loss from your home. Insulate your attic as much as you can. If possible update the ventilation. Some of the pre WWII homes you can’t ventilate well if at all. The insulation is the most important part. For you DIYers go to your local lumber yard and purchase some bats of fiberglass insulation we really like Owens Corning and line your attic. Here is a link to their instructions to insulate your attic.
Otherwise hire a local insulator and they can spray insulation into your attic. Our insulator of choice is Dave Stanton owner of Northwind Insulation in Northfield.
While I can agree with your observation that many homes are poorly insulated and have areas were heat loss from the home causes problems and should be focused on to remedy, there are many factors as to whether a COLD ROOF will stop ice dams. With so many architectural challenges by poor designs, dormers, gables, cathedral ceilings, getting to a cold roof via ventilation can be difficult and extremely costly. Your article does not address a basic fact of Mother Nature… THE SUN. What do you do about radiant heat from the sun everyday? Most homes will see some sun exposure during the day. That heat melts snow and creates moisture on the roof, typically following the slope to the eaves and valleys. Then the temperature drops and the melt refreeze. If this happens over a couple of days… ICE DAM! Even on a well vented cold roofs like you have described. Keeping valleys, eaves and gutters clear can only be achieved by keeping the refreeze from occurring by keeping the melt liquefied and allowing it to get off the roof and then too the ground. There are products out on the market that can prevent ice dams and keep them from forming. Checkout http://www.thermaltechusa.com and see them in action.