Commercial Metal Roofing in Troy, MI

Panels are locked together on site with a powered seaming machine that folds the seams over. A double-lock seam, folded 180 degrees, is the one to ask about for low slopes that need extra weathertightness, and it suits cold regions with freeze-thaw cycles. Depending on the profile and the design, some mechanically seamed panels can go on slopes as low as 1/2 inch per foot, and the code's floor for standing seam systems is 1/4 inch per foot.

The panels are held by concealed clips, with no screws through the face of the roof. Expansion clips have a sliding part that lets the panel move as the steel grows on a July afternoon and shrinks on a January night, which matters on long panel runs. The catch: a double-lock panel is harder to replace if one gets damaged.

Snap-lock panels have formed edges that click together without a seaming machine, which makes them quicker to install. The trade-off is slope: they generally aren't recommended below 3 inches per foot. On commercial buildings that usually means mansards, entry canopies and steep sections over offices, not the main low-slope roof.

Ribbed panels lapped side to side and screwed through the face, common on pole buildings, older warehouses and equipment sheds. They go on without seaming equipment, and their weak points are the screws and washers: as the panels expand and contract, the screw holes can enlarge until screws loosen and back out. The code requires galvanized fasteners on steel roofs unless the manufacturer specifies otherwise, and allows stainless steel on any metal roof. If a few panels need replacing, ask whether your rib profile is still made, or the patch will never quite match.

A retrofit builds light-gauge steel framing on top of the existing flat roof, tied into the building's structure, and sets a new sloped metal roof on it. The Metal Construction Association says its members have engineered these systems for more than four decades, that the framing is engineered to keep the roof structure sound and the new roof designed to current wind and gravity loads, and that the space between the old roof and the new one can take added insulation. That structural review belongs in the scope.

For a building whose flat roof has leaked for years, a retrofit can end the ponding for good. Ask whether the old membrane stays in place under the framing, how the new eaves, gutters and downspouts tie into the existing drains, and who signs the structural engineering.