Inspecting metal roofs....You can absolutely walk the roof surface if it's considered safe to walk on. No snow or rain.
You should consider the following items when performing a roof inspection on a metal roof: A) panel corrosion B) loose fasteners at panel laps and C) seriously deflected panels.
An especially important area to inspect thoroughly is the system’s roof seams. The five primary components of the seam-fastened metal roof assembly are...
1) Horizontal panel seams
2) Vertical panel seams,
3) Panel fasteners,
4) Metal panels
5) Perimeter and penetration flashings.
Deterioration of one or more of these components is the most common cause of roof leakage. Horizontal seams occur where the bottom edge of a roof panel overlaps the top edge of the downslope panel. As panels expand and contract, sealants within these seams become brittle. Foot traffic, expansion, contraction and other forces deflect the panel seams, resulting in broken seals and open seams. Strong winds, negative building pressure or ice damming during periods of freezing and thawing might force water up the slope and into the building through these voids.
Vertical seams occur where the sides of adjacent panels overlap. Similar to horizontal seams, sealant deterioration and panel deflection also reduce a vertical seam’s integrity and allow water entry in conjunction with wind, negative building pressure, or ice damming.
Panel fasteners typically contain neoprene sealing washers to prevent water infiltration. Ultraviolet exposure and panel movement from expansion and contraction normally deteriorate these washers. The fastener holes also elongate from panel movement, and in some instances, the holes are larger than the washers. Overtightening fasteners during installation immediately damages the washers and increases their susceptibility to deterioration.
Loose, missing and rusted fasteners are common deficiencies, too. Steel panels, by their makeup, are susceptible to deterioration over time. Common deficiencies include rusting, kinking, puncturing and finish deterioration. If an inspector suspects leaks from panels’ end laps, make sure sealant is present and located in front of the fastener, not behind it.
Also, note if the sealant is cracked or dried. Inspect panel terminations at the eaves, ridges and valleys to ensure closure strips are in place. These strips are made of foam or rubber and fit under the panel to keep out water and animals. Also, inspect the trim pieces at the rakes to ensure they are sealed and fastened properly. Look for buckling or standing water at the laps of the panels, which indicates unusual movement within the system.
Perimeter and penetration flashings are common locations for leaks. The effects of panel movement are concentrated at these locations, thus accelerating deterioration of sealants, fasteners and other flashing components. Premature flashing problems can arise from poor design and installation. Quality workmanship and appropriate flashing material are vital to long-term flashing and roof performance.
While walking over the roof, you should make sure to inspect penetrations, the source of most leaks. you'll need to verify that the sealant is soft and pliable where the field and flashing meet. Fasteners should be tight, and neoprene washers should be in good shape, and not cracked or dried.
Metal systems typically are installed on a slope, so drainage is not a concern. But they usually drain via gutters, either exposed or concealed, so you should check gutters and downspouts to ensure they are free of debris and restrictions. If the roof slope is very shallow, you should look for ponding or restricted drainage in the roof field. Panel deflection sometimes can cause dips, which trap roof water.