Roof shingles are almost always highly visible and so are an important aspect of a building’s appearance in patterns, textures and colors. Roof shingles, like other building materials are typically of a material locally available. The type of shingle is taken into account before construction because the material is affected by the condition of the structure. All shingle roofs are installed from the bottom upward beginning with a starter course and the edge seams offset to avoid leaks. Many shingle installations benefit from being placed on top of an underlayment material such as asphalt felt to prevent leaks even from wind driven rain and snow and ice dams in cold climates.