The answer to 'lifespan of underlayment' is that the typical lifespan of roof underlayment is 20-30 years, depending on the type of material and the climate conditions. Underlayment is the protective layer installed beneath the roof shingles or tiles, and it plays a critical role in protecting the roof deck from moisture and weather elements.
Asphalt-saturated felt paper is the most common and affordable type of underlayment, with a lifespan of 20-25 years. Synthetic underlayments, made from materials like polypropylene or polyethylene, can last 25-30 years or more. Metal and rubberized underlayments are the most durable, with a lifespan of 30-50 years. The actual lifespan of your underlayment will depend on factors like the quality of the material, proper installation, and the local climate conditions.