and a triple metal layer depicted by reference b comprised of the thicknesses of the trough material outer fold 34 and inner fold 36 this also creates in a preferred embodiment gap 38 which is an optional feature of the present invention the front containment wall border area of trough 30 of fig3 is depicted with an inwardly projecting containment shelf 39 that is described in co pending u s application ser no 09 880 412 owned by the assignee of the present invention the entire extent of mounting field 20 need not rest against the building from which runoff is collected the assignee of the present invention has used an aluminum alloy as well as copper based metals for trough material 11 but as those in the field will understand other materials may be employed to advantage with the present invention in a preferred embodiment outer fold 34 extends from apex 33 to apex 35 of inner fold 36 while inner fold 36 extends from apex 35 to its end 37 to preserve clarity in the figures end 37 of inner fold 36 is shown in fig6 there are several sizes of half round gutter trough available for example the assignee of the present invention offers 6 u2033 half round troughs these and other sizes of troughs may be fabricated in conformity with the present invention using standard sized materials i e coil stock of approximately 11 and u215e inches in width in the western u s and 11 and u00be inches in parts of the eastern u s.