There are two types of fastening systems for metal panel roofs: through-fastening and concealed clips.
Through-fastening systems use fasteners that penetrate the metal panels. These have gaskets designed to keep the penetration from leaking. Large-head screws with neoprene washers are the most common type. Fasteners are often exposed and are typically driven through areas where panels overlap and/or through other locations specified by the manufacturer.
Because through-fasteners don’t allow metal to freely expand and contract. Expansion and contraction of the metal roofing panels ocurs due to temperature changes, and possibly movement of the underlying structure. This can cause through-fasteners to loosen or back out over time. Metal roofing with loose or missing fasteners will suffer reduced wind resistance and possible leaking problems.
Clip-fastening systems use clips that fasten directly to the roof deck. They are incorporated into the panels at the seams, which leaves the clip concealed from view. They allow for expansion and contraction of the panels. Clips are usually found on the better quality roofing systems.
Fasteners not designed for use with metal roofing can be a problem due to corrosion, inadequate strength, or failure to allow for thermal expansion and contraction of metal panels. It’s always best to use clips specifically designed for metal roofing.