InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
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.
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.
[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.
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.
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]
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.
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.
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.
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
[Bold faced roofing suppliers in the list below provided technical information quoted or adapted in the article above - Ed.]
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 Alliance www.metalroofing.com
Continue reading at METAL ROOF EXPOSED FASTENER SPACING or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see METAL ROOFING - home
Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
(Nov 24, 2011) Carolyn Dutton said:
We just had a metal roof installed on our house in Sanibel, FL It has exposed fasteners. What would you expect to have in a guarantee?
Carolyn many modern metal roof systems include a generous life-expectancy guarantee for the roof covering, often 20-40 years of life. However the warranty most likely will exclude leaks due to installation defects as well as mechanical damage (such as a tree limb falling on and puncturing the surface of the roof).
If one or more of the exposed fasteners was not properly installed (wrong location, missing a sealing washer, screwed in on an angle so that the fastner does not seat properly, insufficient number of fasteners or improperly placed fasteners that fail to protect against wind damage) then those defects may cause a leak or damage and may not be covered by your warranty.
I recommend that you ask your installing roofer for a copy of your roof warranty and that you read it carefully. Typical roof warranties cover the material, often pro-rated by actual roof age, and will not cover labor needed to repair or replace the roof.
at WARRANTIES for ROOF SHINGLES we include more information about common roof product warranties.
(Aug 3, 2014) Lisa Greenlee said:
Our metal roof was installed in the early 80's. A previous homeowner installed skylights incorrectly. Now we cannot find anyone who will work on our roof to replace the skylights. Our roof has exposed fasteners. We've had 4 roofing companies come out to look (all who work on metal roofs) they all say they cannot help us but they can replace our entire roof. How can I find out the manufacturer of our roof?
I'd take some photos of the roof profile and fasteners and send them or take them to metal roofing suppliers first in your area and second perhaps online.
We understand that the subsequent roofers may be worried about being blamed for other roof leaks or snafus, or they may not know the proper flashings to use with this particular roof. But let me say it sounds a bit greedy to refuse to repair a metal roof and to insist on a complete replacement if the only problem is at skylight flashings.
I add that exposed fastener metal roof systems in SOME cases were not designed for residential properties and may leak in other spots besides fouled up flashing.
Use our CONTACT link to see our email and send along photos that may permit further comment.
(Sept 17, 2014) Jim said:
In a high wind area, how far apart should the screw lines be and how many screws should be in a row?
Roofing manufacturers (such as www.dimond.co.nz 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 sheet is fastened to every structural member (purlin, rafter, truss, etc).
The New Zealand company I cite gives a nice little table of number of fasteners per metre as a function of wind zone
Low wind zone (32 m/sec) 1 fastener per meter (figure a meter as the running length along the structural member such as rafter or truss)
Medium wind zone (37 m/sec) : 2 fasteners per meter
High wind zone (44 m/sec) : 3 fateners per meter
Severe wind zone (50 m/sec) : 4 fasteners per meter
But be sure to check with the manufacturer of the roofing product you intend to use.
Also there are other fastener details that are important besides choosing an approved fastener type, such as an assmuption that the fastner is driven in perpendicular to the roof surface (not on an angle).
High wind one (44 m/sec) : 3 fasteners per meter
Please see details about fastener spacing for metal roofs at
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
Terne II - Classic Terne-Coated Steel ... is a new and improved version of historic Terne metal, ... Terne II has improved capability for resisting corrosion in all environments ... also has excellent formability, solderability, and affinity for paint ... without compromising mechanical characteristics. It can be used in flatlock, standing seam, vertical wall designs and virtually any other application in which original Terne has been used. It is strong and ductile, having high yield and tensile strengths as well as workability. This new material can easily be formed with conventional roofing tools.
With Terne II roofing, it is advisable to paint the material as soon as conditions permit. Oxide formation is slower than with the original Terne and the wait for proper painting conditions provides substantially less risk. The new material is coated with Follansbee's new ZT® alloy, a combination of zinc and tin. This coating is designed not only as a barrier but also to be anodic to the steel substrate and reduce the potential for oxidation before painting.
The traditional oil-based paints long required on original Terne are not recommended for application on Terne II. Follansbee's Rapidri paint with its faster drying time and ease of application is much superior to the old painting system. The Rapidri acrylic paints are aesthetically pleasing while offering enhanced durability and color retention. ...