Corrugated Metal Roofing Installation Standards

Underlayment

• Corrugated metal panels, like other roofing material, are fastened to some type of roof decking, either solid, such as oriented strand board or "strip sheathing," or 1-by-4-inch boards nailed across rafters. Solid sheathing is used most often on houses while the strips are used on sheds and barns. It also should be installed over a waterproof membrane or roofing paper to further protect the wood sheathing. On houses, it frequently is placed on top of rigid foam insulation fastened to the decking or sheathing.

Washer Caps on Screws

• Install corrugated metal panels with screws that have a plastic washer cap at the head, which seals the screw hole to prevent moisture from getting in. Three-inch nails can be used, but also must have sealing caps. Screws should be driven into the decking in the corrugation valleys until the washer cap is firmly seated against the metal. It usually requires about 20 screws per panel, placed 12 to 18 inches apart, although this will vary with the width and length of the roofing.

Overlaps

• Overlapping of panels is key to a good installation. Panels come in varying widths with various coverage widths, but all allow for an overlap, typically one ridge and one valley of corrugation. Screws through both pieces seal the overlap. Panels come in different lengths, from 6 to 20 feet, and often more than one row is required between the eave and the peak of a roof. These panels should be overlapped by about 6 inches, from the top.

Seams and Edges

• When more than one row of panels is required, the top row should be started with a half-panel, cut lengthwise, so the seams of the panels do not align. Panels also should be placed so there is a slight overhang at all edges of the roof. These edges and the peak where two roof angles meet need to be sealed with special edge and peak caps, made to conform to the corrugations, to prevent water from getting under the metal. Some corrugation styles use "filler" strips on the edges to seal the gap between decking and metal.

Building Codes

• Always check local building codes before beginning a corrugated metal roof project. Some areas subject to high winds or heavy snow loads may have stricter installation standards. Some building or zoning codes also may prohibit or regulate use of corrugated metal panels on houses.