A carpenter is flashing a new window opening in a wall that will receive stucco as its exterior finish. The building code requires a two-stage rainscreen system. After installing the sill pan flashing, which step is most crucial to ensure proper water management for this type of wall assembly before window installation?

Question: A carpenter is flashing a new window opening in a wall that will receive stucco as its exterior finish. The building code requires a two-stage rainscreen system. After installing the sill pan flashing, which step is most crucial to ensure proper water management for this type of wall assembly before window installation?

Answer options:

• Install the side and head WRB pieces over the window flange.
• Apply continuous sealant along the back of the window's nailing flange. ✅ Install a secondary drainage plane (e.g., dimpled membrane) over the sheathing and WRB, extending into the sill pan.
• Fasten plywood bucks around the rough opening to ensure a tight fit for the window.

Correct answer: Install a secondary drainage plane (e.g., dimpled membrane) over the sheathing and WRB, extending into the sill pan.

Explanation: For a two-stage rainscreen system, particularly with stucco, creating a significant drainage gap and a secondary drainage plane is critical. Installing a dimpled membrane or similar material over the WRB and sheathing, and ensuring it directs water into the sill pan, provides the necessary secondary drainage and gap for effective moisture management in case of primary WRB failure. The other options are general flashing steps but do not specifically address the 'two-stage' requirement of a rainscreen.