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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 for ROOF 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
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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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.
Installation Specifications for Standing Seam Metal Roofs
On 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.
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?
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
[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
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.
Metal Roofing Suppliers
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?
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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Frequently Asked Questions (FAQs)
(Feb 3, 2012) New Metal Suppliers - Update said:
Question: underlayment for metal roofs installed atop existing roof surfaces?
AUTHOR:Anonymous (no email)
COMMENT:We have a project which has a steel truss roof system with a structural metal deck diaphragm (B deck type for seismic requirements)installed over the steel trusses.
We want to provide a standing seam roof over the structural metal deck. Slope is 3:12 and the attic is a cold attic. Do we have to provide any underlayment between the structural deck and the standing seam roof? Or can we just install the standing seam roofing directly over the structural deck. (The structural deck grooves are running perpendicular to the slop of the roof). Any assistance for the best installation procedures will be appreciated. You can reply to this e-mail: email@example.com.
You will probably need to install underlayment - being safer against galvanic or other corrosive problems and you might need more. Here are some example specifications from Best Buy Metals - bestbuymetals.com but you will want to check the installation specifications for the specific brand you are buying.
Also check standing seam height alternatives. 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.
Here is another example specification from the Summit Pacific metal sales standing seam roof installation guide:
Question: can I add just partial snow guards on my metal roof?
(Oct 31, 2014) Mary said:
We see lots of metal roofs on which installers provided snow guards ONLY over entrances or other spots where there is extra risk. As long as snow falling off of other sections of the roof are not going to cause trouble, your approach is fine.
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