What type of flashing is installed in mortar joints and folded downward to cover the base flashing?

The correct choice is counter-flashing, which is specifically designed to be placed in mortar joints and then folded downward to effectively cover the base flashing beneath it. This method provides an effective barrier against water penetration by ensuring that the upper layer of flashing overlaps and protects the lower layer from water intrusion.

Counter-flashing is commonly used in masonry structures, particularly around chimneys, walls, or any point where the roof meets vertical surfaces. By being embedded in the mortar joints, it allows for a seamless appearance and prevents direct exposure of the base flashing to the elements, enhancing the overall waterproofing of the system.

Step flashing and base flashing serve different purposes in roofing systems; step flashing is typically used where a roof meets a wall, overlapping each section like steps, while base flashing is installed at the base of vertical surfaces. Flashing tape, on the other hand, is a self-adhesive material that is used for sealing joints and gaps but does not serve the same purpose as counter-flashing in terms of installation within mortar joints.