McElroy Mega-Rib 36-inch roof profile

Mega-Rib is an exposed-fastener roof and wall panel made by McElroy Metal, with deep trapezoidal ribs on close centers. This article covers the full-width version with 36 inches of installed cover, drawn on McElroy drawing E, sheet 5 of 5, revision B, dated January 26, 2021, and described in the Mega-Rib product data revised April 2, 2025.

The drawing appears in Miami-Dade notice of acceptance 23-0720.05, approved August 10, 2023. It depicts a 24-gauge steel roof section.

A narrower Mega-Rib with 28.8 inches of cover is also drawn in the product data. It is listed for 26-gauge material and has an overall width of 36 1/8 inches. It is a separate panel width from the 36-inch-cover section described here.

The full-width panel has 36 inches of installed cover and an overall formed width of 38 7/8 inches. The difference between the two is 2 7/8 inches.

The major ribs sit at 7.2-inch centers, so five modules make up the 36-inch cover. Each module divides into a 5.08-inch formed-rib portion and a 2.12-inch pan flat, which together equal 7.2 inches.

• Installed cover: 36 inches
• Overall formed width: 38 7/8 inches
• Major rib pitch: 7.2 inches
• Major rib rise: 1 1/2 inches
• Major web angle: 45 degrees
• Crest flat: 2.12 inches
• Pan flat: 2.12 inches

The section runs from a flat pan up a sloping web to a broad flat crest and down a descending web before the next pan. Ribs on 7.2-inch centers are closer than the 12-inch centers of PBR and R-panel profiles.

The 2021 approval drawing specifies 24-gauge steel with a minimum panel thickness of 0.023 inch. The 2025 product data lists 24-gauge steel as standard, with 22-gauge also available and a 26-gauge option for the full-width panel that depends on the manufacturing facility.

Panels are roll formed at the factory in standard lengths up to 40 feet. Longer lengths are handled by inquiry.

The product data shows foam inside closures and foam outside closures matched to the profile, and two fastener patterns: one at eaves, ridges and endlaps, and one at intermediate purlins.

In the installation drawing, one outer rib of a panel is placed over the neighboring rib, with the joint at the outermost high point of the profile. A continuous 1/8-inch by 1-inch roll tape sealant runs the length of the panel at the side laps. The installation manual requires it on all roofs and recommends it on walls where water intrusion is critical.

The October 2023 installation manual gives these fastening details for roof panels:

• Roof panels are fastened with #12-14 x 1 1/4-inch long-life fasteners with washers.
• Stitch fasteners are spaced at 1 foot 8 inches on center, with the exterior side of the sheet pre-drilled before erection.
• Trim is attached with 1/4-14 x 7/8-inch Lap Tek fasteners at every other rib or at major ribs, depending on the detail.
• Head and jamb trim use #10-16 x 1-inch TEK2 pancake head fasteners every 2 feet on center.
• Horizontal wall panels are fastened at 1 foot on center.

The installation manual groups its drawings into wall details and roof details. The roof details are eave, eave with gutter, end lap, intermediate purlin, ridge, rake, rake off-module, high side eave and trim lap.

At the eave, the trim runs from outside wall to outside wall and trim pieces lap 2 inches. Butyl tape sealant measuring 3/32 inch by 3/8 inch is applied in the trim laps, and the trim is pop riveted. A continuous run of 1/8-inch by 1-inch butyl tape goes on top of the eave trim, closures are set in the tape, and a further run of roll tape sealant goes on top of the closures before the roof panels are fastened.

The wall details cover base, simple base, wall panel to girt, outside corner, off-module corner, head and jamb conditions in vertical and horizontal orientations. Base trim is set 1 1/2 inches down the face of the finished floor, and a 1/8-inch gap is left between trim and panel. Head trim has weep holes drilled in the field as required.

The Mega-Rib product page lists 24-gauge Galvalume as standard, with 22-gauge available on inquiry, 26-gauge in narrow coverage, 26-gauge in full coverage at the Adelanto plant only, and 18- and 20-gauge painted Galvalume in limited availability. Standard 26-gauge coverage is 28.8 inches at all plants except Adelanto, where it is 36 inches. The page lists 36-inch coverage as available on request at other plants. Factory panel length is listed as up to 50 feet on the page and up to 40 feet on the product data sheet.

• Finishes: Kynar 500 (PVDF), silicone modified polyester (SMP) and Galvalume Plus, an acrylic-coated finish in 24 gauge
• Minimum slope: 1:12, with tape sealant at the side laps on all slopes
• Substrate: solid deck or open framing
• Orientation: vertical or horizontal
• Onsite forming: not offered
• Fire: UL 263 Class A
• Uplift: UL 580 Class 90
• Impact: UL 2218 Class 4
• Air and water infiltration: ASTM E1680 and E1646
• Other listings: ASTM E1592, IAPMO UES listing, ICC-ES ESR-5896, Florida Product Approval 1832.8 and 1747.6, and Miami-Dade
• Plants: Clinton, IL; Peachtree City, GA; Adelanto, CA; Sunnyvale, TX

Mega-Rib is one of McElroy's exposed-fastener panels. Panels at other covers and gauges are separate drawn sections, and the 28.8-inch-cover Mega-Rib shares the name but not the 36-inch cover, the 38 7/8-inch overall width or the 24-gauge approval drawing.

The panel is used on walls as well as roofs. Its close-spaced ribs are specific to the Mega-Rib roll set, and the dated drawing identifies which revision of the section is meant. Roof applications of this kind appear in the exposed-fastener metal roof panel category.