Flush seam panels typically are installed on a vertical surface or used as soffit. As the name describes, the seams on these panels are behind the metal and fastened to the plywood, all you see is a line at the seam. There is a hollow space behind each panel, typically 1” thick. The nature of these panels is that on a vertical surface they tend to let in a very small amount of moisture into the seam, however with the correct flashing at the bottom of the panels the moisture is exited to the outside of the building. You will see this particular product more on commercial buildings than on residential houses, unless it is used where the owner wants a superior soffit system.