For roof slopes of 3 units vertical in 12 units horizontal and over, what is the minimum width for valley flashing underlayment?

The minimum width for valley flashing underlayment in roofs with a slope of 3 units vertical in 12 units horizontal or greater is determined by building codes and best practices in roof construction. A width of 36 inches provides adequate coverage to prevent water infiltration and to accommodate the drainage needs of the roofing system.

In the case of valleys, which are critical areas where water runoff converges, having sufficient underlayment width helps ensure that any water flowing down the roof is effectively managed. A width less than 36 inches could leave certain areas of the valley vulnerable to leakage and water penetration, especially in heavy rain or snow conditions.

Choosing a width like 36 inches also allows for sufficient overlap with other roofing materials, enhancing the overall waterproofing integrity of the roof structure. In contrast, widths less than this may compromise the roof's weather resistance, leading to potential damage over time. Thus, the standard of 36 inches is set to ensure reliable performance and protection for the building beneath.