For roof slopes from 2:12 up to 4:12, how many layers of underlayment should be applied?

For roof slopes between 2:12 and 4:12, it is recommended to apply two layers of underlayment. This requirement is based on the increased risk of water intrusion that comes with shallower sloped roofs. A single layer may not provide sufficient protection against water seepage, especially in regions that experience heavy rainfall or when ice damming occurs. The second layer enhances the waterproofing properties and serves as an additional barrier, helping to prevent leaks and extend the lifespan of the roofing system. This is particularly important because the lower the slope, the more challenging it is to shed water quickly, making adequate underlayment crucial for a durable roof installation.