Metal roofing examples (C) Daniel Friedman Exposed Fastener Metal Roof Panel Systems

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Metal roof installation:

This article explains the selection, applicability, and installation specifications for exposed fastener metal roof systems, also referred to as barn roofing, or agricultural building roof systems.

Because this roofing material is also sometimes used on residential buildings, homeowners and home inspectors should also review this material when diagnosing roof problems.

This article series discusses best practices in the selection and installation of residential roofing. This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Our page top photo shows an exposed fastener roof on a utility building at the Summerblue Arts Camp, Two Harbors, MN.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Exposed-Fastener Panels for Metal Roof Installations

Exposed fastener metal roof errors (C) Daniel FriedmanAdapted/paraphrased with permission from Best Practices Guide to Residential Construction, chapter on BEST ROOFING PRACTICES:

Steel and aluminum panel roofing with exposed fasteners has been a popular choice on agricultural buildings for decades. In recent years, these “ag panels” have grown increasingly popular for rural homes as well, since they can provide a long-lasting roof at a cost comparable to asphalt shingles.

[Click to enlarge any image] At left is an exposed metal faster roof on a barn in Dutchess County, New York, in the U.S.

The metal roofing products installed on homes, while essentially the same material as the agricultural panels, generally use better metal coatings, and installers pay more attention to sealing and watertight detailing.

While a carefully installed exposed-fastener roof should be free of leaks upon completion, small installation errors can result in leakage later as the metal panels undergo normal thermal movement that places stress on the fasteners. With so many exposed holes in the panels, periodic inspections are recommended. Also, the exposed fastener heads, in addition to lending a rural look to the building, tend to catch leaf debris and restrain sliding snow.

Metal roof topics we will discuss include: Designs of panels used in exposed-fastener metal roofs. Set proper metal roof panel length to avoid buckling with exposed fastener systems. Proper metal roof exposed fastener type and location for exposed-fastener metal roof panels.

Installation guide for agricultural building roofing or "metal barn roofing". Characteristics of metal roofing materials: exposed fasteners, barn roofing, other exposed fastener roof systems. Best practices for exposed fastener metal roofing material installation, flashing, ventilation, nailing, underlayment.

Materials used in Exposed-Fastener Metal Roofs

Figure 2-36: Exposed fastener roof panels (C) J Wiley, S BlissExposed-fastener panels are typically 26 to 29 gauge, compared to the heavier 22 to 26 gauge used in standing-seam roofing.

The ribs in exposed fastener roofing are also lower and closer together than in standingseam roofing and may be squared, rounded, or v-shaped (see Figure 2-36).

Most exposed fastener or "barn roofing" panels are 2 to 3 feet wide and formed with galvanized steel, Galvalume®, or aluminum.

Panel length. While some stock sizes are available, ordering panels factory-cut to exact lengths simplifies installation and reduces corrosion at field cuts.

Panels can be ordered in any shippable length, although excessive thermal movement can be a problem for steel panels longer than 40 feet or for aluminum panels longer than 16 feet.


Reduce Metal Roof Panel Lengths To Avoid Buckling

In regions with very wide temperature swings, contractors should use shorter lengths - see “Thermal Expansion” in Table 2-10, shown just below. [Click any image or table to see an enlarged view.]

Table 2-10: Thermal expansion on metal roofs (C) J Wiley, S Bliss

[Click to enlarge any image]

Installation Methods for Exposed-Fastener Metal Roofs

Metal roof installation in Norway (C) Daniel FriedmanWhile traditionally installed over battens, most panels in residential installations are now installed over a solid plywood deck with minimum No. 30 felt underlayment.

Metal roofing manufacturers recommend plywood over oriented-strand board (OSB) due to plywood’s better screw-holding ability. Roofing felt should be installed with plastic cap nails rather than metal buttons, which can deteriorate the metal roofing by galvanic action.

Our exposed-fastener metal roof installation shown at above-left is located in Molde, Norway.

Align the metal roof panel to eaves. After installing drip edges and valley flashing, the first panel is fit along one rake, square to the bottom edge of the roof. If the roof is not square, the first panel may need to be cut at a bevel along the rake. Start at the downwind end of the roof, so the edge of each overlapping panel faces away from the prevailing winds.

Cutting exposed fastener metal roof panels. Where panels need to be cut, use snips or shears rather than an abrasive blade, which overheats the steel coatings and leaves a rough edge prone to rust. Abrasive blades also produce hot metal filings that can embed in the paint and cause rust on the face of the panels.

Side and end laps on exposed fastener metal roofs. After the first panel is screwed down, the next panel is set in place, lapping over the first. Side laps are typically sealed with butyl tape and held together with gasketed sheet-metal screws. Where more than one panel is used up the run of the roof, the upper panel laps the lower by 6 inches and is sealed with butyl tape.

Fasteners used on exposed-fastener metal roofs.

Figure 2-37: Metal roof fasteners (C) J Wiley, S BlissFasteners are typically special wood screws with integral EPDM or neoprene gaskets that compress under the screw head to seal the hole.

Fasteners should be driven at a right angle to the roof plane and should be snug but not so tight as to deform the washer (see Figure 2-37 above). Nearly all manufacturers recommend placing screws in the flat sections between ribs.


Although making holes in the flat section may seem unwise, placing screws in the ribs is discouraged for two reasons - check out our photo at left.

Exposed fastener metal roof errors (C) Daniel FriedmanFirst, the long exposed screw shaft passing through the rib is prone to snap over time due to thermal movement of the panels. Second, it is easy to overdrive the screws and crush the panels.

Higher-cost EPDM washers are less likely to leak than neoprene.

Take a closer look [click to enlarge] at fastener location and the "too-tight" bolting on the exposed fastener metal roof on this northern Minnesota building.

Compare this roof installation to the Norway metal roof shown above.

Reroofing Using Exposed Fastener Metal Roof Panels

Panels can go directly over a single layer of asphalt shingles in good condition. If the shingles are curled or uneven, install 2x horizontal purlins at 16 inches on-center. In either case, put down a new layer of No. 30 underlayment before installing the panels.

-- Above material on exposed metal fastener roofing installation procedures was adapted with permission from Best Practices Guide to Residential Construction.

Exposed Fastener Metal Roofing Fastener Spacing Schedule

Exposed metal fastener roof, Akaroa New Zealand (C) Daniel Friedman

Roofing manufacturers (such as Fabral in the U.S. and Dimond in New Zealand) give installation specifications for their product including screw fastener spacing schedules (and other data such as unsupported spans, unsupported overhang, and different fastener types).

Typically the fastener spacing is specified as number of fasteners per square (say 75 or 80 fasteners) but an allowance must be made for more fasteners when installing exposed fastener metal roofs in high wind zones.

Details of metal roof fastener spacing distances or schedules along with photo examples are provided in a the next article in this series, found at



Resources: Roofing Materials & Equipment Suppliers


Metal Roofing

[Bold faced roofing suppliers in the list below provided technical information quoted or adapted in the article above - Ed.]

Venting Underlayments

Benjamin Obdyke Cedar Breather, a 3/8 -in.-thick matrix-type underlayment designed to provide ventilation and drainage space under wood roofing

Metal Roofing Materials, Methods, Standards

Metal Roofing Alliance


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