AERZ civil structural consulting Inc. has done structural assessment of a commercial unit roof at south east Calgary. The owner of the commercial wanted to add a new heavy HVAC unit on top of the roof. The structural assessment found that the roof will not be safe by 25% if the HVAC unit will be installed on the roof (25% over stressed than allowable design values). The roof trusses are wood steel open web trusses with steel tube sections as vertical web members and wooden upper and lower horizontal chords held together by pins. An Engineering solution was provided to owner to support the roof trusses carrying the HVAC unit.