Will a Metal Roof Work on a Flat Roof?

Corrugated or Structural Panel

• The basic metal roofing options are corrugated sheets of either aluminum or galvanized steel, or structural panels, frequently called standing seam. Corrugated panels are generally thin material, composed of alternating ridges and valleys, with ridges typically 2-1/2 inches apart at the peaks and valleys 1/2-inch deep. Standing seam panels are usually heavier metal, with broad flat sections and vertical seams, usually about 2 inches high at regular intervals.

Overlapped vs. Interlocked

• Corrugated panels are installed with panel edges overlapped, typically by one ridge and one valley. Standing seams are interlocked, formed with a straight edge on one panel inserted into a slot or groove on the adjoining panel, similar to tongue-and-groove wood. Both types are typically installed with aluminum or galvanized screws with plastic washer caps to seal the screw holes.

NRCA Recommendations

• Both corrugated and structural panels are used for roofing, but the National Roofing Contractors Association recommends only structural panel for flat or low-slope applications because of its superior hydrostatic or water barrier capability. The interlocking seams form a better barrier against water runoff than the overlapping panels of corrugated metal.

Structural Support

• The NRCA says structural or standing seam panels also provide more structural support than corrugations. Both types can be installed over wood decking, on rafters or on "strip sheathing" of boards nailed across rafters at fixed intervals, generally 24 inches. Corrugated panels often need extra support on flat or low-slope roofs, which hold snow and ice more than sloped roofs and are more subject to weight forces. Structural panels also may need more support on flat roofs in areas of very heavy snow accumulations.