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

  • METAL ROOF EXPOSED FASTENER SYSTEM - CONTENTS: Exposed fastener metal roof systems. 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
  • POST a QUESTION or READ FAQs about exposed fastener metal roof systems: installation, troubleshooting, repair
  • REFERENCES

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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.

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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.

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.
See GALVANIC SCALE & METAL CORROSION

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.

Exposed fastener metal roof errors (C) Daniel Friedman

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.

First, 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 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

METAL ROOF EXPOSED FASTENER SPACING

 

 

 

Resources: Roofing Materials & Equipment Suppliers

Manufacturers

Metal Roofing

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

  • Atas International www.atas.com Modular metal shingle, tile, and standing-seam panels
  • Classic Products www.classicroof.com Modular metal shingle panels and standing seam panels
  • Custom-Bilt Metals www.custombiltmetals.com Modular metal shakes and standing seam panels
  • Dimond Roofing Systems, Tel: 0800 DIMOND, Website: http://www.dimond.co.nz The company has offices throughout both North Island and the South Island of New Zealand, of which we give just a few

    Dimond Roofing Systems, Auckland, 48 Victoria St, Onehunga, New Zealand, Ph: 09 634 0575 Fax: 09 634 6231
    Dimond is New Zealand's largest manufacturer of steel roofing, cladding, structural and rainwater goods.

    Dimond Roofing Systems, Christchurch, 89 Buchanans Rd, Hornby, Ph: 03 336 0045 Fax: 03 342 3670

    Dimond Roofing Systems, Whangarei, 33 Rewarewa Rd, Ph: 09 438 1539 Fax: 09 438 6525
  • Decra Roofing Systems www.decra.com Modular metal shingle, tile, and shake panels
  • Dura-Lok Roofing Systems www.duraloc.com Modular metal roofing shingles with granular coating
  • Fabral Corporation: Lancaster PA, USA, www.fabral.com Tel: 800-477-2741, Exposed fastener and concealed clip metal roofing panels
  • Gerard Roofing Technologies www.gerardusa.com Modular metal shake and tile panels with granular coating
  • Met-Tile www.met-tile.com Modular metal roof-tile panels
  • Zappone Manufacturing, website www.zappone.com/
    Zappone Manufacturing, 2928 North Pittsburg St. Spokane, WA 99207 1-800-285-2677, Washington State Copper Roofing Supplier of Copper scallop shingles, copper shingles, copper bay windows, vertical walls, aluminum roof shingles

Venting Underlayments

Benjamin Obdyke www.benjaminobdyke.com 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 www.metalroofing.com

 

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