Having your roof replaced, as can be imagined, is a noisy, dirty and invasive home improvement.  By avoiding the problem of ice dams, and letting them wreak havoc on the structure of your home, you are inviting a big roof repair in the future years.  Not only can the ice and water affect the roof, but gravity takes over and causes the water to run down into the interior of the home and causes water damage and can even be the cause of mold.

Roofing material is expensive, and if you only plan on having this job done once, then you will want it done right.  A quality installation is required to avoid running into these problems again.  Be prepared to fork over a pretty penny to contractors to ensure that the job is done well and correctly.

Your roof is the one element of your home that is directly exposed to all the elements.  No other part of the home sees as wide a variety of seasonal elements as the roof.  It is a major home improvement, and chances are you would only have it done it you had to because of damage.  The trick is to prevent the damage by properly taking care of your roof and getting it ready for the onslaught of winter.

Source:  http://kingstonroofing.ca/why-roof-replacement-is-a-major-home-improvement-project