Abstract: A secondary drainage system for buildings utilizing pre-manufactured exterior panels. The system drains off moisture and condensation collected in joints and on the rear wall of the panels, under circumstances where the primary exterior seal or cladding have failed. An elongated collection channel is attached in inclined relation to the rear wall of a panel. The channel includes a top cover, comprised of a trough having inclined walls and oval apertures. The lower end of the channel includes an end cap with a drain tube, connected to an upper, inner portion of a receptacle box. The receptacle box is located within a vertical joint between two adjacent panels. A lower, outer portion of the receptacle box has a one-way discharge valve. Also provided are intermediate joint gutters, having open tops and a discharge outlet positioned over the trough of a collection channel.