This article explains exactly how to check your roof to make sure there are no places where water can leak in or heated air can leak out. The article includes:"Roofs are actually the first line of defense against rain, snow, cold air and harsh weather in gener al. And so if you're smart, you'll want to check what kind of shape yours is in twice a year. That means being on the look-out for missing shingles or deteriorated flashing (the metal that seals bends and joints on skylights, chimneys, etc.). More than 90 percent of roof damage occurs in these two areas, and catching it early can be key to preventing bigger problems". There are more tips in the article.