Hello Solver - Thanks for your interest. What I am calling "orthogonal roof planes" would consist of two roof planes whose slopes are at right angles to each other. In my case, picture a simple L shaped floor plan, one level house. The longer, upright rectangular section of the L is covered by a gable roof. The shorter rectangular section of the L is covered by a shed roof that intersects with the right half of the roof plane covering the upright rectangular section creating a valley. A "valley jack truss" is the name I borrowed from " The Graphic Guide to Frame Construction" by Rob Thallon, 3rd. Ed. 1992 , page/detail 150 B, and it refers to those trusses that are placed on the roof plane of the upright section ( and perpendicular to the structural members supporting the gable roof ), in order to support the intersecting shed roof. PS...Another example of this framing detail is illustrated on page 884 of the reference guide to Chief Architect (current) which can of course to accessed online if you don't happen to have a copy of Thallon's Guide to Frame Construction handy. Hope to hear from you. Take care! Fred