Standing seam is the most popular style of metal roofing – both in residential and commercial building industries. It has also been the longest installed type of metal roof, dating back to when all metal roofing was hand-made from sheet metal – usually copper or tin. Today, standing seam roofs are commercially manufactured by tens if not hundreds of big manufacturers, and thousands of smaller roofing outfits with their own sheet metal shops and standing seam roll-forming machines.
We’ve recently added a complete installation guide that walks you through preparing a roof deck and installing roofing underlayment, installing eave, first metal roof panel with gable / rake trim, field panels, sidewall flashing, valley flashing and installation of hip & ridge caps, and includes a hands-on installation video.
Most standing seam metal roofs installed today are 24 gauge steel or .032 aluminum panels with high quality Kynar 500 paint coating, baked-on in seven layers (including primer) in a controlled factory environment when the metal coil is manufactured. After the coil is slit to the right size, it is delivered to the “manufacturer” of metal roofs, and is roll-formed into pre-measured length panels, which can take place on a job site or in a metal shop, and then delivered to the job site, where they are installed on the roof. Most common profiles of standing seam roofs are 16″ panels; they are either snap-lock or mechanical lock profiles. Snap lock standing seam allows installers to quickly install a metal roof by snapping one panel into a receiving lock of the previous panel. Snap lock panels can be installed from left-to-right and vice-versa, and even from a center starter panel in either direction.
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Standing seam metal roofs should be installed over a properly prepared roof deck. The wooden substrate below should be even, dry, and be at least 1/2 inch thick. Standing seam roofs can also be installed over purlins (horizontally running 1×3 or 1×4 furring strips) or over boards. It is also recommended to install standing seam over a roofing underlayment such as roofing felt (tar paper) or synthetic underlayment. It is recommended that synthetic underlayment is breathable, so it does not trap moisture, which can cause the roof deck to rot and mold / mildew can form, causing expensive repairs.
Ice & Water shield is also not recommended for use under a metal roof, as it is first – not serving its main purpose, since standing seam metal roofs can pretty much stop ice dams in their tracks, without any deck damage, while the much glorified Ice & Water shield can trap moisture, and potentially cause mold and deck rotting issues on poorly ventilated roofs — where the deck is not allowed to breath due to inadequately ventilated attic space (which is sometimes the case in some houses), since the ice and water shield seals it off on one of the sides. In Northern New England states (NH, VT and ME), it is a common practice to install a standing seam metal roof over asphalt shingles. — This is done mainly for economical reasons, as a roof tear off and disposal can be very costly. This practice should be avoided, however. Two reasons for this are as follows:
- Standing seam panels will expand and contract with temperature changes, while the under-pan could be rubbing against the stone-coated surface of asphalt shingles. — This could easily strip off the paint and galvanizing layer on metal roofing panels and cause rust.
- When snow sits on a metal roof, it compresses the panels against the asphalt shingles, thereby creating horizontal dents on the panels, which could make your new roof look very unattractive, or should I even say – ugly. This is also referred to as “telegraphing effect”, when rows of shingles show through a metal roof.
A standing seam metal roof is attached to the roof deck using fasteners (usually 1 inch wide head screws) and either clips or screws / nails installed through a nailing strip — a part of the panel formed when the metal panels are being rolled out. Nailing strip panels are faster and cheaper to install, but should not be used on panel runs over 15 feet, as expansion and contraction will cause buckling and “oil-canning” in the panels. Oil canning is the term used to refer to ugly bubbles that you can sometimes see on a poorly installed standing seam roof. To prevent oil canning, you can have your standing seam panels made with special low profile stiffening ribs that are indented into a pan of each panel, during the manufacturing process. Another way to avoid oil canning is to install standing seam panels using special clips (this reduces the tension on the panel), and to install panels in mild weather, so it’s not too expanded or contracted at the time of installation, and of-course you need a more or less even roof deck surface.
Pros and Cons of Standing Seam:
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While standing seam roofs are very popular, they are rather difficult to install on complicated (complex and cut-up) roofs, with many dormers, skylights, valleys, etc. They can be very pricey compared to other systems such as metal shingles, shakes and stone coated steel roofing profiles. The difference in cost is mainly due to the difficulty of installation, high materials waste factor, and higher-premium materials cost for quality standing seam panels (please note that this not the same as 29 gauge, cheaper, thin-grade steel, acrylic-coated metal roofs that are normally installed by low-ball companies) made of high-grade Galvalume steel or aluminum.
Because of the design of architectural standing seam, it is also rather difficult to install a roof penetration flashing for sky-lights and chimneys, as there is no one good flashing method, and you rely mainly on caulking, when it comes to water-tightness. All of these factors complicate standing seam installation process and make your initial costs go up.
Low slope roof applications:
A standing seam metal roof can be installed on a low slope roof of no less than 1 in 12 pitch. It must be a mechanical lock standing seam system, and is usually a structural standing seam, installed on space metal buildings. The mechanical lock profile used on low-sloped metal roofs ensures that water does not penetrate through the lock between panels, if it sits above the lock. Some structural standing seam profiles that are made of steel with lower quality galvanic coating, and may begin to rust within 10-15 years, and may require a metal roof coating application.
Near-Flat and Low-Slope Roofs:
Metal roofs should never be installed on completely flat roofs, with no slope at all, as they are not designed to withstand ponding water and all joints on a metal roof are sealed using some type of caulking. Even the copper panels with soldered seams have been proven to leak on dead zero slope roofs. While, most interlocking metal shingle profiles can only be used on roofs with at least 3 to 12 roof slope, standing seam, can be successfully installed on many roofs with 1 to 12 roof slope (a roof with a very low slope), but you must use a mechanical lock profile to prevent any unwanted roof leaks.
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