A cubic foot of ice weighs 57.2 pounds, more than 5 pounds less than a cubic foot of water. Unlike most other substances, ice expands as it freezes.
Because ice is less dense than water, it floats on the surface of water as it forms. If it became denser, like most other substances, it would sink to the bottom of ponds and lakes. During the cold months, these bodies of water would become solid blocks of ice, so thick that even the warmest of days would transform the surface to slush.
The weight of ice and snow on a roof has the potential to cause winter disasters. While snow, which is a crystalline form of ice, is lighter in weight than solid ice, each cubic foot of snow adds 17 pounds per square inch to the roof. Homes in areas prone to heavy snowfall require special engineering to support the load.