Side note: You shouldn't aim to prevent heat from escaping entirely. In fact, rather than over-insulating, you'll want to ensure that the highest point in your house, usually the attic, has proper ventilation to let out the hot, moist air that collects in any building where humans live. That's because, during the winter, your roof needs to stay at a uniform temperature to prevent the formation of ice dams. These occur when the middle of a roof is warm but its edges are cold. In these conditions, snow will first melt and then refreeze, forming a large chunk of ice on the eaves, which blocks the slush from falling off the building. Instead, it might leak into your home, leaving you with a much higher repair bill.