The answer to 'average cost of underlayment' is that the cost can vary significantly depending on several factors. Underlayment is a key component of a roofing system, providing a protective barrier between the roof deck and the shingles or other roofing materials.
The main factors that influence the cost of underlayment include the type of material (asphalt-saturated felt, synthetic, or rubberized), the quality and thickness, the size of the roof, and the local market conditions. In general, you can expect to pay anywhere from $0.50 to $2.00 per square foot for quality underlayment materials. It's important to get local quotes from roofing professionals to get an accurate estimate for your specific project.