The answer to 'how long does underlayment last' is that the lifespan of roofing underlayment can vary widely, but it typically lasts between 10-30 years depending on the type of underlayment and the local climate conditions. Asphalt-saturated felt paper underlayment generally has a lifespan of 10-20 years, while synthetic underlayments can last 20-30 years.
The longevity of underlayment is affected by factors like sun exposure, moisture, and foot traffic. In hot, sunny climates, underlayment may deteriorate faster than in cooler regions. Proper installation and maintaining the roof surface are also key to maximizing the lifespan of underlayment. If the underlayment shows signs of wear or damage, it's recommended to have a professional roofing contractor evaluate the roof and replace the underlayment as needed.