What is the minimum horizontal overlap required for underlayment beneath asphalt shingles on roof slopes between 2/12 and 4/12?

The minimum horizontal overlap required for underlayment beneath asphalt shingles on roof slopes between 2/12 and 4/12 is 19 inches. This overlap is essential to ensure water has a proper drainage path and to prevent water from seeping through joints or seams in the underlayment. Roofs with low slopes, such as those between 2/12 and 4/12, are particularly vulnerable to water intrusion, so the manufacturer and building codes typically stipulate a larger overlap to enhance water resistance. By providing this substantial overlap, the underlayment can better protect the underlying layers and the building structure from moisture issues that can arise due to precipitation.