What is the purpose of underlayment or waterproofing membrane in roofing?

The purpose of underlayment or waterproofing membrane in roofing is primarily to protect against leaks. These materials serve as a barrier that prevents water from seeping into the building structure, especially in areas prone to heavy rain or snow. They are typically installed beneath the primary roofing material and act as an additional line of defense against moisture infiltration.

Underlayment can be especially critical in areas where the primary roofing material might be less effective at shedding water, such as in low-slope roofs or at seams and joints. By effectively sealing off vulnerabilities in the roof, they significantly extend the lifespan of the roof and maintain the integrity of the underlying structure.

It's important to note that while insulation, aesthetics, and weight may also be considerations in roofing systems, they are not the primary functions of underlayment or waterproofing membranes. Their main role is to provide essential waterproofing features that protect against leaks, making option B the correct choice.