All steep-slope roof systems (i.e., roofs with slopes of 25 percent or more) have five basic components:

1. Roof covering: shingles, tile, slate or metal and underlayment that protect the sheathing from weather.
   
    
2. Sheathing: boards or sheet material that are fastened to roof rafters to cover a house or building.
   
    
3. Roof structure: rafters and trusses constructed to support the sheathing.
   
    
4. Flashing: sheet metal or other material installed into a roof system's various joints and valleys to prevent water seepage.
   
    
5. Drainage: a roof system's design features, such as shape, slope and layout that affect its ability to shed water.