To reduce peak discharge on existing stormwater infrastructure, many city jurisdictions are revising their stormwater management requirements for developments and redevelopments. Achieving this goal includes increasing capacity of on-site storage and slower release of stormwater runoff. At sites primarily occupied by the building footprint, a blue roof, also known as a controlled flow roof drainage system, is an option to detain stormwater and satisfy these requirements. This article will focus on blue roof design considerations, including selecting a waterproofing system that accepts long-term ponding water and ensuring the structure can accommodate the weight of the detained water and imposed roof deflections.