Architectural metal roofs have a lot going for them. They look great, are suitable for relatively low pitches, and can last 60 to 100 years. But, they need to be properly installed.

As with all roofing, keeping water out comes down to material choice and proper detailing. Using the manufacturer-supplied flashing and trim are obviously important but here are some other things to consider.

Standing Seam is Worth the Cost

Roof panels come in exposed fastener and standing seam types.

Exposed fastener roofs can have 70 screws per square—a lot of potential leaks. The weak points are the neoprene gaskets, which can begin leaking in as little as 15 or 20 years. And if installers drive the screws at an angle or don't tighten them enough, the gaskets won't make a proper seal to begin with.

By contrast, standing seam roofs have no exposed fasteners. Panels are fastened along the vertical seams, using clips or an integral flange, which is then covered by the next panel. Standing seam costs more but has a better shot at a trouble-free life.

Be Careful With Add-Ons

Even on standing seam roofs, some installers fasten solar panels, satellite dishes or snow guards with exposed screws. A better choice is to use S5 brackets, which clamp to the vertical seams and are held in place with round-point screws that don't penetrate the metal.

Underlayment is Crucial

If any water does get behind the panels (whether from installation errors or leaks caused by falling branches) it can work its way into the sheathing around those screw penetrations.

That's where a high quality, peel-and-stick underlayment membrane earns its keep. It provides a backup watershed and also self-seals around screws.

Some installers only extend the membrane 36 inches up from the exterior wall line, as required by code, then lay roofing felt above that. This protects the roof edge against leaks caused by ice dams, but if water gets behind the metal on the upper part of the roof, remember that felt has no sealing ability.

Underlayments Aren't Equal

Although you can use a standard peel-and-stick membrane, some builders and architects want more protection. The issue is heat: underlayment beneath a metal roof will get hotter in the sun than under asphalt shingles.

"We make a membrane for metal roofs called Ice & Water Shield HT. It's a 40 mil rubberized asphalt that has been tweaked to give it better thermal stability," says Brandon Wulf, a Sales Manager at GCP Applied Technologies. "The HT product is formulated slightly differently to achieve a higher thermal stability."

Some roofs get even hotter. That's the case with copper panels, which absorb more sunlight than steel, and in extreme climates like Arizona. "In those cases, we recommend Grace Ultra," says Wulf. "It's 100 percent butyl rubber with a thermal stability up to 300 degrees."

Bottom line: careful fastening and the right underlayment go a long way toward keeping a standing seam roof trouble-free for its entire service life.

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