Abstract: A roof jack is provided for mounting an air conditioner of the evaporative type on a pitched roof of a structure wherein is provided an upper frame member adapted for hinged connection with a lower frame member and said lower frame being adapted to serve as a plenum for connection to supply ducts and to contain a removable damper for preventing escape of air from the structure through the supply ducts and said upper and lower members and said upper and lower frame members being adapted for levelling by the use of prefabricated extension panels for the sides of said upper panel through which fixing screws may be inserted and fasten the sides of the upper member to the lower member.