Maximizing Metal Roofs

by Kevin Ernster, RRC

Metal roofing systems on the market today have evolved into reliable, long-term systems. Panels can be constructed out of galvanized steel, stainless steel, aluminum and copper, depending on the application that is required.

Inspection Challenges
The first step in establishing an inspection and maintenance program is to identify the type of system that is installed on your facility. Metal roof systems fit into one of two categories:
Architectural systems are classified as water shedders because their seams are not rollformed, as is the case with structural panels. They are usually flat panels that snap together or use a cover strip at the seams to join the panels. Typically, they are installed on steeper slopes with shorter panel lengths. Due to their flat design, they have minimal load-carrying capacity. Because of this minimal capacity, they are installed over another substrate, such as plywood.
Structural systems have load-carrying capacities and do not require a substrate for support. Structural capacity is built into the panels by the use of trapezoidal breaks placed in the metal pans at seams. Panel seaming is accomplished by rollforming the seams or lapping the panels and install- ing a fastener through the panel.

The inspection process for metal systems is similar to that of other roofing systems. Conduct a walkover of the roof to identify drainage characteristics, as well as deficiencies in the field and around projections. Perform walkovers at least once a year and after major weather changes. On structural systems, be sure to walk over the underlying purlins to check for panel deflection.

Deficiencies to look for in metal systems are different than those in other systems. The following items should be inspected: 

• panel corrosion
• loose fasteners at panel laps
• seriously deflected panels

At all fastener locations, particularly older seam fastened systems - deterioration of the neoprene washers that seal the fasteners to the panel is common. More difficult to detect, but also common on older systems, is elongation of the fastener hole. After years of expansion and contraction, the hole where the fastener penetrates the panel can become larger than the washer. You may need to remove fasteners to visually verify this condition.

If you suspect leakage from the end laps of panels, make sure sealant is present and that it's located in front of the fastener, not behind it. Also note if the sealant is cracked or dried. Inspect panel terminations at the eaves, ridges and valleys to assure that closure strips are in place. These strips are made of foam or rubber and fit under the panel to keep weather and animals out of the roof. Inspect trim pieces at the rakes to ensure they're properly sealed and fastened. At the laps of the panels, look for buckling or standing water, which indicates unusual movement within the system.

As you walk over the roof, inspect penetrations, where most leaks occur. Verify that the sealant is soft and pliable where the field and flashing meet. Fasteners should be tight, and neoprene washers should be in good shape, not cracked or dried.

Metal systems typically are installed on a slope, so drainage is not often a concern, but they usually are drained by using gutters, either exposed or concealed.  The inspection process also should include looking into gutters and downspouts to ensure they are clear of debris and restrictions. If the roof slope is very shallow, look for ponding or restricted drainage in the roof field. Panel deflection can sometimes cause dips in the field, which trap water.

Making Repairs
When repairing a metal roof, never use asphaltic based roof cement. This material becomes hard and brittle and cannot accommodate movement found in metal systems. Once this material is used, it's very difficult to remove and replace it with an appropriate material. For small areas of corrosion, follow the procedures below:

• sand the panel lightly
• apply a rust inhibiting primer
• coat with a Kynar-based finish to match