Slate is considered to be the most sophisticated of all roof types. If it is installed correctly, a slate roof can have a life expectancy of hundreds of years. The lifespan depends on the type of slate used, the roof configuration, and the geographical location of the property. Slate roofs are expensive and special skills are required to install and repair them. They also should be inspected at least once a year to assess the overall condition and to check for loose nails and broken or missing slate. Broken tiles allow moisture and UV light to directly attack the sheet asphalt underlayment.