All edges are butt. Huebert Fiberboard wood fiber insulation board can be used in conjunction with various single ply membrane systems. The individual manufacturer of each system must approve of the intended use of our product as a substrate. There are many different single ply systems, and each system has its own specific requirements and needs. Huebert Fiberboard wood fiber insulation can not be exposed to an open flame (torched on system). Huebert Fiberboard roof insulation makes a good substrate insulation in re-roof situations, providing the existing roofing or insulation is clear of debris, fairly level, and moisture free.