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Metal roofing examples (C) Daniel Friedman Standing Seam Metal Roof Systems

  • STANDING SEAM METAL ROOF INSTALLATION - CONTENTS: Standing seam metal roof systems. Installation guide standing seam roofing. Flashings and Accessories for Standing Seam Metal Roofs. Snow guards or snow brakes on metal roofs. Best practices for standing seam metal roofs
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Standing seam metal roofs:

This article explains the proper installation, fastening, and flashing details for standing seam metal roofs. Standing-seam roofing consists of individual panels that run the length of the roof with a high rib up each side of the panels.

The ribs overlap and lock together, concealing the fasteners and giving the roofing its name.



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Standing-Seam Metal Roofing Installation Practices & Details

Metal roofing examples (C) Daniel FriedmanAdapted/paraphrased with permission from Best Practices Guide to Residential Construction, chapter on BEST ROOFING PRACTICES:

The hidden fasteners allow thermal movement in the panels and are less likely to leak than exposed fasteners. However, some trim pieces are still fastened with exposed screws.

The smooth surface of a standing-seam roof provides a cleaner appearance and is easier to keep clear of leaf debris than tile, wood, or other textured roofing surfaces.

Also, it can be walked on when necessary. Snow slides off easily as well, making this a popular choice in high snow regions. The cost is generally 25% to 50% more than an exposed-fastener roof of similar materials.

Materials Used in Standing Seam Metal Roofs

Standing-seam panels are 8 to 24 inches wide and available in steel, copper, and aluminum with a wide array of finishes (discussed below). Stiffening ribs may be added to wider panels to reduce waviness (oil-canning). Thicknesses for quality residential applications are typically 24 or 26 gauge, but lighter and heavier stock is also available.

Standing seam metal roof installers can form panels on-site from coil stock with portable roll-forming equipment, or they can order factory-made panels from a growing number of metal roofing manufacturers. Most factory-made panels have snaptogether seams, eliminating the need for special crimping equipment used by site fabricators. In most cases, panels are fabricated to run from eaves to ridge, eliminated the need for end lap joints.

Figure 2-42: Standing seam metal roof fasteners (C) J Wiley, S Bliss

Installation Specifications for Standing Seam Metal Roofs

Metal roofing examples (C) Daniel FriedmanOn new homes, most panels are installed over a solid plywood deck with minimum No. 30 felt underlayment. Metal roofing manufacturers recommend plywood rather than OSB due to plywood’s better screwholding ability.

Install the felt with plastic cap nails rather than metal buttons, which can cause corrosion when in contact with the roofing panels.

See GALVANIC SCALE & METAL CORROSION.

After installing the drip edge, install the first panel, making sure it is square to the bottom edge of the roof. If the roof is not square, pull the panel away from the rake so the first rib does not overhang the rake edge.

Later, the rake trim piece will cover any small discrepancies. If the panels have an integral screw flange, keep the screws just snug so the panels can move with temperature changes. The clips are designed to allow thermal movement.

The next panel fits over the first with an overlapping rib. Fit each panel to a line snapped up the roof, marking the edge of each panel. Without layout lines, the panels can build up an incremental error, throwing off the layout. As panels are installed and secured, the joints are easily locked together with hand pressure.

Traditional standingseam roofing required special motorized crimpers to lock the seams. While these are still used on some low-slope systems, most residential installations now use snap-together panels. Unless the layout works perfectly, the last panel will need to be cut along the opposite rake and bent with a hand seamer to form the end rib.

Reroofing Using Standing Seam Metal Roofs Over Other Roof Coverings?

Standing seam reroof over wood shingles (C) Daniel Friedman

Our standing seam barn roof re-roof photo (left) demonstrates that re-roofing with standing seam metal roofs over older buildings is a very old practice.

In this case the barn roof originally was covered with wood shingles, installed when the barn was constructed in the late 19th century in upstate New York.

Many installers will not install standing-seam roofing over existing asphalt shingles since the rough surface will tend to bind the panels and cause “oil-canning,” as the panels move with temperature changes.

One option is to install the new metal roofing over 2x4 purlins nailed through the old roofing and shimmed to form an even plane.

Follow manufacturer’s recommendations for spacing of purlins, typically no more than 24 inches on-center.

Flashing and Sealing Details for Standing Seam Metal Roofs

Figure 2-41: Metal Roof Flashing details (C) J Wiley, S Bliss

[Click to enlarge any image]

Typical standing seam metal roof flashing details are similar to those found in Figure 2-41 shown at left .

Manufacturers of preformed roofing panels provide eaves and rake flashings, ridge caps, and sidewall flashings in matching finishes, as well as coil stock for site fabrication.

Many flashings are designed with hidden fasteners; others require exposed gasketed screws. If you want to see the original installation details for the plumbing vent shown at above right, take a look at the photos and text at the bottom of our article
on PLUMBING VENT DEFECTS & NOISES.

Temporary roof vent flashing while waiting for metal roof installation (C) Daniel Friedman Eric Galow Permanent roof vent flashing for metal roof installation (C) Daniel Friedman Eric Galow

Follow manufacturers’ recommendations regarding which sealants to use for compatibility with the roofing (typically butyl tape, or gunnable terpolymer butyl or urethane sealant).

In general, avoid acid-cure silicone (the type that smells like vinegar) as it can be corrosive to many metal finishes.

-- Adapted with permission from Best Practices Guide to Residential Construction.

Resources: Roofing Materials & Equipment Suppliers

Manufacturers

Metal Roofing Suppliers

Venting Underlayments

More Information about Roofing Materials, Methods, Standards

Standing Seam Metal Roof Seam Heights

Reader Question: 20 January 2015 Jack said:

What should be the minimum height of the standing seam for a 1.5"/12 roof?

Reply:

Jack,

The flange system metal roof is typically made with a seam height of 1 1/4" - also referred to as "Eco" seam by some manufacturers.

Flat or "Dutch" or locking type standing seams range in height from a low of about 1" to 2 3/8" with taller seams generally used on lower slopes.

For relatively low slopes like the 3:12 you cite you may need to go to the higher seam height to protect against leakage, especially in a snow-climate. For roofs you describe that are as low slope as 1.5 in 12, in a snow climate where there is risk of ice dams I I question if a standing seam roof would be recommended by some manufacturers.

But Atlas Roofing describes standing seam roofing products used for low slope roofs described as sloped to 2:12 or less over solid substrate. These roofs are covered with a locking type standing seam that is 2 3/8" in height.

OPINION: Watch out: even with a tight, tall locking standing seam roof, if your low -slope roof is subject to ice dams, snow blockage or any other condition that could cause water backup-s on the roof such that the water depth can ever exceed the seam height you can expect leak trouble.

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Continue reading at LIFE EXPECTANCY of METAL ROOFS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see SNOW GUARDS on METAL ROOFS for more examples of conditions and leaks on standing seam metal roofs.

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