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ROOFING INSPECTION & REPAIR
AMERICAN CEMWOOD ROOFING
BEST ROOFING PRACTICES
BUILT UP ROOFS
CATHEDRAL CEILING VENTILATION
CERTIFICATIONS for ROOFING CONTRACTORS
CHIMNEY FLASHING Mistakes & Leaks
COLD WEATHER ROOF TROUBLE
DECKS, ROOFTOP CONSTRUCTION
EPDM, RUBBER, PVC ROOFING
EXTRACTIVE BLEEDING on SHINGLES
FIRE RETARDANT PLYWOOD
FLASHING on BUILDINGS
FLAT ROOF MOISTURE & CONDENSATION
Green House or Solarium Roof Leaks
HEAT TAPES & CABLES on Roofs for Ice Dams
ROOF ICE DAM LEAKS
MASONITE WOODRUF FIBERBOARD ROOFING
NOISE CONTROL for ROOFS
PLASTIC ROOFING TYPES
PVC, EPDM, RUBBER ROOFING
ROOF ARCHITECTURAL STYLES - PHOTO GUIDE
ROOF CLEANING RECOMMENDATIONS
ROOF COLOR RECOMMENDATIONS
ROOF INSPECTION SAFETY & LIMITS
ROOF LEAK DIAGNOSIS & REPAIR
ROOF NOISE TRANSMISSION
ROOF REPLACEMENT SNAFUs
ROOFING FELT UNDERLAYMENT REQUIREMENTS
ROOFING MATERIALS, Age, Types
SADDLE CONSTRUCTION at CHIMNEYS
SNOW GUARDS & SNOW BRAKES
STANDARDS for ROOFING
STRESS SKIN INSULATED PANELS
TEST LABS - ROOF SHINGLE
TREES & SHRUBS, TRIM OFF BUILDING
TRUSSES, Floor & Roof
UNDERLAYMENT REQUIREMENTS on ROOFS
VENTILATION in BUILDINGS
WALK-ON ROOF SURFACES
WARRANTIES for ROOF SHINGLES
WORKMANSHIP & ROOF DAMAGE
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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Adapted/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.
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
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.]
[Click to enlarge any image]
Installation Methods for Exposed-Fastener Metal Roofs
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.
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.
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.
-- Adapted with permission from Best Practices Guide to Residential Construction.
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
Continue reading at LIFE EXPECTANCY of METAL ROOFS or select a topic from the More Reading links shown below.
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