Building an accessory dwelling unit (ADU) is more than adding square footage. It requires every part of the structure to be built with long-term durability in mind, starting with the roof. For this new ADU in National City, we installed a complete asphalt shingle roofing system designed to protect the new structure from day one. After preparing the roof deck, Titanium PSU self-adhered underlayment was installed to provide a durable waterproofing layer beneath the finished roof. Because self-adhered underlayment seals around fasteners, it provides an added level of protection against wind-driven rain and moisture intrusion. The roof was finished with Owens Corning Duration architectural shingles in the Mountainside color, giving the new ADU a clean, modern appearance while providing a durable roofing system built for Southern California's climate. Whether it's a new home, an addition, or an ADU, installing the right roofing system during construction is one of the best opportunities to build lasting protection into the structure before the walls and finishes are complete.