How should the first membrane be installed in a BUR system?

In a Built-Up Roofing (BUR) system, the first membrane is crucial for managing moisture and ensuring the long-term performance of the roofing system. Installing the first membrane as a vapor retarder is essential because it helps to prevent moisture from penetrating into the insulation and structure below.

A vapor retarder effectively minimizes the movement of moisture through the roofing system, which is especially important in areas where vapor drive can be a concern, such as in cold climates or in buildings with high humidity levels. By acting as a barrier, it helps to keep the insulation dry, maintaining its thermal resistance and preventing deterioration of building materials.

Considering the other options, placing the membrane as a loose layer would not provide the necessary adhesion and protection against moisture infiltration. Installing it tightly to the roof deck could be beneficial, but if the role of a vapor retarder is overlooked, moisture issues might arise. Lastly, installing only along the edges does not provide the continuous barrier needed across the entire roof surface to effectively manage vapor movement. Thus, the installation of the first membrane as a vapor retarder is critical to ensuring the integrity and performance of the BUR system.