Software architecture documentation helps people in understanding the software architecture of a system. In practice, software architectures are often documented after the fact, i.e. they are maintained or created after most of the design decisions have been made and implemented. To keep the architecture documentation up-to-date an architect needs to recover and describe these decisions. This paper presents ADDRA, an approach an architect can use for recovering architectural design decisions after the fact. ADDRA uses architectural deltas to provide the architect with clues about these design decisions. This allows the architect to systematically recover and document relevant architectural design decisions. The recovered architectural design decisions improve the documentation of the architecture, which increases traceability, communication, and general understanding of a system.