As you are aware, asphalt-saturated and asphalt-impregnated felt underlayments are the most common steep-slope roof underlayments. These types of underlayments are appealing because of their ease of installation, ability to perform intended functions and relatively low cost.
A steep-slope roof system underlayment performs several functions, such as:
Also widely available are synthetic and composite products often touted by manufacturers as being stronger, lighter or better weathering alternatives. The following will examine current standards and building code requirements for underlayments used with steep-slope roof systems.