Concrete and clay tile roofs with a pitch of less than 4:12 require how many layers of underlayment?

Concrete and clay tile roofs with a pitch of less than 4:12 require two layers of underlayment to ensure adequate water resistance and to prevent leaks. The reason for this requirement is that roofs with a low pitch are more susceptible to water accumulation and infiltration. Having two layers of underlayment helps create a more effective barrier against moisture, providing additional protection in areas where the roof slope may not allow for quick drainage.

Additionally, the layering system helps to account for potential issues like wind-driven rain, ensuring that if water makes it past the outer tile layer, the underlayment will provide a second line of defense. This is a critical consideration in maintaining the integrity and longevity of the roofing system under varying weather conditions. The use of two layers is a widely accepted practice within roofing standards for low-slope applications involving concrete and clay tiles.