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Exposed Fastener Metal roofing installed in Hamner Springs, New Zealand (C) Daniel Friedman Fastener Screw or Nail Spacing Tables for Exposed Fastener Metal Roof Panel Systems

Spacing recommendations for exposed fastener metal roof systems:

This article describes the fastener screw or nail schedule for several types of exposed fastener metal roof systems, citing manufacturers' installation manuals and guidelines. We include a discussion of the requirement for use of a greater number of metal roof fasteners in high wind zones and we give an example schedule of the number of screws recommended for metal roofs at various wind speeds or wind zones.

This article series 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. Our page top photo illustrates the fasteners on an exposed fastener metal roof installed in Hamner Springs, New Zealand.

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Exposed Fastener Metal Roofing Fastener Spacing Schedules & Tables vs Wind Load

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

At above left: a diagonal patterned, minimally-fastened exposed metal fastener roof panel system in the field of the roof on a building in Akaroa, New Zealand. But notice the closer fastener spacing on the roof's hips.

[Click to enlarge any image]

Where purlins are used in roof structure construction in this area, for wind damage protection a fastener may be installed on every other raised rib along the roof's eaves.

Below : two photographs of an older exposed metal fastener roof on St. Cuthbert's church in the Port Hills area above Christchurch, New Zealand, you can see fasteners in every other rib of this exposed fastener roof.

At below right you can see the fastener schedule for roofing panel edges along the roof valley. [St. Cuthberts church, built in 1874, was severely damaged in recent Christchurch area earthquakes.

While the church itself is not currently in use the congregation still meets nearby.]

 

Reader Question: (Sept 18, 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?

Reply: Fastener Screw Spacing Distances for Metal Roofing

Jim,

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).

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

Typically the sheet is fastened to every structural member (purlin, rafter, truss, etc). But that does not give the spacing distance between the fasteners along the structural member - that's what you must be asking.

Here are two common examples of metal fastener spacing for exposed fastener metal roofs. We give more detail in after introducing the wind speed topic:

You don't say where you live, but wind speeds and wind zone ratings are indeed a critical consideration in choosing a roof covering material itself as well as its fastener schedule. For example in Welllington New Zealand, average windspeed (measured at the Wellington airport) is 29 km/h - compare that with the Windy City (Chicago) where average wind speed is a piddling 18 km/h. In Wellington New Zealand wind speeds top gale force most of the year (288 out of 365) recorded at 104 km/h in the spring of 2014. Wellington's highest reported wind gust speed was 248 km/h. - Fitzimons, (2011).

Exposed Metal Roof Fastener Schedule versus Wind Speeds or Wind Zones

Exposed fastener metal roof installation in Dunedin, New Zealand (C) Daniel Friedman

The roof shown at above left is installed on a building in Dunedin, New Zealand.

Dimond, the New Zealand company I cite above and in our resources list below gives a table of number of fasteners per metre as a function of wind zone ranging from 1 fastener per meter to 4 fasteners per meter.

Based on our example wind data above, had the roof at above left been installed in Wellington we'd have expected to see 4 fasteners per meter. [Click to enlarge any image]

Watch out: be sure to check the metal roof fastener schedule 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 assumption that the fastener is driven in perpendicular to the roof surface (not on an angle).

Fabral provides additional metal roofing fastening advice for Exposed Fastener type roofs that generally agree with Steve Bliss's original material in the article above and which we excerpt here:

FABRAL can supply either screws or nails for fastening into dimension lumber. [The company notes that nails are not recommended for fastening aluminum roofing because of thermal movement] Always use screws with solid sheathing.

Screws for use with steel panels are galvanized and then coated with an organic polymer for optimum corrosion resistance. For best results with aluminum panels, use #300 series stainless steel screws.

The FabrOseal® galvanized ring-shank nail, with its premium long- life silicone rubber gasket, assures a lasting seal and is the best nail available for steel panels when screws are not the method being used by the installer.

The correct way to fasten steel panels with nails is to drive the nail through the top of the rib so the washer is compressed securely against the metal. Nail placement must be in the ribs for roofing applications to minimize the potential for roof leaks. Over-driving the nail can split the washer and dimple the metal, causing leaks.

Wood screws with combination metal and neoprene washers should be installed in the flat area of the panel adjacent to the ribs, and tightened such that the washer is compressed as illustrated above. This will ensure a lasting, leak-proof seal.

Remove any metal filings created by the drilling action of the screws or pre drilling of the holes to avoid rust staining on the panel surface. Refer to the fastening schedules in this booklet for the correct fastener locations. - Fabral (2012)

Exposed Fastener Metal Roofing Installation Manuals

Metal Roofing Information & Product Sources

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


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