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Thermal Blocks
In an effort to achieve more thermal efficiency, some standing seam roof systems use a "Stand-Off Clip" that supports the roof panel above the roof purlin. A rigid foam "Thermal Spacer" or "Thermal Block" was then installed in the resulting gap between the purlin and the roof panel. This system provides a thermal break between the roof and the building purlin keeping the purlins from sweating in the cold or adding heat to the building in the summer.
When Roof Huggers are installed over a thermal block system they will compress the foam blocks (usually 1" in thickness) 3/8" - 1/2" depending on the panel and foam density. Roof Huggers are over-cut to allow for this pull down, however thermal blocks are generally not used at the building eaves and therefore the Roof Huggers installed at the eave should be 3/8" - 1/2" lower in height to keep the new roof in plane.
Roof Hugger does have a system that accommodates these systems. It requires a special Hugger with a “Anti-Rotational” Arm and a special self-drilling patent pending screw that enables the existing roof panel and Hugger to bear 1” above the existing purlin. In some cases, Roof Hugger will recommend using a extra long screw with a sleeve that accomplishes the same thing. When this box is checked Roof Hugger will ask for more details before fabricating the sub-purlin order and may call for more details before quoting the project.