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 roofs, dating back to when all metal roofing was hand-made from sheet metal – usually copper or tin.
Today, standing seam metal roofs are commercially manufactured by tens if not hundreds of big metal roofing manufacturers, and thousands of smaller roofing outfits with their own sheet metal shops and standing seam rolling machines. Here is how standing seam metal roof is manufactured.
We 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 metal roof 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 the 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, either on site or in the 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 – either snap-lock or mechanical lock profiles. Snap lock allows the metal roofing contractors to quickly install the roof by snapping one panel into receiving the lock of the previous panel.
Snap lock panels can be installed from left-to-right or vice versa, or even from a center starter panel in either direction.
Standing seam metal roof installation
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 boars. It is also recommended to install standing seam metal roofing 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 it’s main purpose, since metal roofs inherently prevent ice dams, and Ice and Water will also trap moisture.
In Norther 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 roof tear off and disposal can be very costly. This practice should also be avoided however. Two reasons for this are:
- Standing seam panels will expand and contract with temperature changes, while the under-pan will be rubbing against the stone-coated surface of asphalt shingles, which will strip off the paint and galvanizing layer of the metal roofing panels and cause rust.
- When snow sits on a metal roof, it compresses the panels against the asphalt shingles, creates horizontal dents on the panels, which 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 the 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, which can be formed when the metal panels are produced.
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 a term used to refer to ugly bubbles that you can sometimes see on a standing seam roof. To prevent oil canning, you can have your standing seam metal roof made with special low profile stiffening ribs that are indented into the pan of each panel, during manufacturing process.
Another way to avoid oil canning is to install the standing seam roof using 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
While standing seam roofs are very popular, they are rather difficult to install on complicated roofs, with many dormers, skylights, valleys, etc. They can be very pricey compared to other metal roofing materials such as metal shingles, shakes and stone coated steel roofing profiles. The difference in cost is mainly due to the difficulty of installation, high waste factor, and higher material cost for quality metal roofing panels (not the 29 ga cheap steel, acrylic-coated metal roof normally installed by low-ball metal roofing companies).
Because of the design of architectural standing seam metal roof, it is also very 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 the installation process of standing seam metal roofing and make the cost go up.
Standing seam on low slope roofs.
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. Structural standing seam is often made of cheaper steel with low quality galvanic coating, and can begin to rust within 10-15 years, and will require a roof repair, as well as fastener re-tightening.
Metal roofs should never be installed on dead flat roofs as it is 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 proven to leak on dead zero slope roofs. Most interlocking shingles profiles can only be used on roofs with at least 3 pitch. As for standing seam, it can be used on very low slope roofs, but you must use the mechanical lock profile to prevent roof leaks.
Written by Leo - roofer with a vision. Follow Leo on Google+