Metal roofing systems on the market today have evolved into reliable and long-term systems.  The use of high-tech finishes gives the panels the ability to withstand harsh environments and the panels now are constructed to any length required through the use of equipment that forms coil stock into panels at the job site.  Panels can be constructed out of galvanized steel, stainless steel, aluminum and copper, depending on the application that is required.

A properly installed metal system can provide many years of maintenance-free performance.  Many of the problematic conditions noted below usually appear on systems that are 15-20 years old.  The key to trouble-free performance is ensuring that the roof is properly designed, installed and maintained.  Improperly installed seams, panel laps, hips and valleys are difficult--if not impossible--to repair if the defect is built into the system.

Inspection challenges
Inspection and maintenance of metal roof systems require different techniques and materials than those associated with built-up or single-ply systems.  The first step in establishing an inspection and maintenance program is to identify the type of system that is installed on your facility.

If you know the system manufacturer, obtain their installation manual to verify how the roof is assembled.  There is usually a nameplate fastened at the gable end of the building indicating the manufacturer.

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 roll-forming the seams or lapping the panels and installing a fastener through the panel.

Structural panels can be installed in low-slop applications at a minimum of 1/4 inch per foot.  Both types of systems use a variety of surface finishes.

Structural systems usually are attached by concealed clips secured to the substrate that hook over the panel.    The clips float free, allowing the panels to move through expansion and contraction without restraint.  Older, less expensive systems are fastened to the substrate through the panel with screws.  On larger span buildings, clips are the only acceptable means of attachment, as expansion forces are intense enough to tear the panels in mechanically attached systems.

The inspection process 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.  When inspecting the roof field, look for:

• 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.

A little more difficult to detect, but also common on older systems, is elongation of the fastener hole in the panel.  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 caves, 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 indicating unusual movement within the system.

Problem areas
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.  If water is ponding behind a projection, try to improve the drainage.

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.

As you progress through your inspection, carry a socket wrench the same size as the panel fasteners.  This lets you remove fasteners for inspection and tighten loose fasteners.  Also, use a roof plan to note where deficiencies exist.  If repairs are required, such a plan makes it easier for the person making the repairs to find them.

Making repairs
Repairing a metal roof may involve different techniques and materials.  Whatever repair is required, do not 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 is very difficult to remove and replace with an appropriate material.  For small areas of corrosion:

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

On larger areas of corrosion, you may need to apply an elastomeric coating formulated for use on metal roof systems.  For perforated panels, depending on the type of system, you might need to replace the panel.  If your system is a structural standing seam, panel replacement is difficult.  Depending on the amount of perforation, you might need to replace the panel.  If your system is a structural standing seam, panel replacement is difficult.  Depending on the amount of perforation, you might need to overlay the panel or coat it with a reinforcing mesh and liquid coating.  Replace seriously deflected panels if they are creating ponded water.

Deterioration of neoprene washers requires removing the fastener and replacing the washer.  If the fastener hole is elongated, replace with an oversized fastener and washer.  Replacing the sealant at the panel laps may require removing the fasteners so sealant can be applied under the panel's leading edge.

All sealants for metal systems should be a high-quality butyl-based caulk.  If there is extensive repair required for the fasteners or panel laps, consult with a metal roof coating supplier on the use of coatings over troubled areas.

Penetration repairs are similar to field repairs.  Replace deteriorated sealants and washers and fasteners as required.  Again, if deterioration is extensive, you may need to use a liquid-applied coating.  Drainage problems can be either very easy to correct--cleaning a gutter, for example--or very difficult.  Such is the case with a large area of deflected panels where sections of roof require replacement to correct.

Beyond repair
If your roof leaks continually and is in an irreparable condition, you might want to consider reroofing.  One option short of replacing the entire panel system is to overlay it with a singly-ply membrane.

Some custom systems are specifically designed for this application.  These systems consist of placing a layer of insulation--usually expanded polystyrene--in panels up to the seam height.  This is then overlaid with an added layer of mechanically fastened insulation to form a smooth substrate.  The single-ply membrane is mechanically attached to the existing metal roof or purlin system.

Another reroofing option is to apply an elastomeric coating over the entire roof.  These systems consist of a multi-layer application of the coating with a reinforcing mesh.  Mesh is placed between the coatings at stress locations, such as at panel laps and penetrations.

One advantage of the coating system is that it is available in a variety of colors to match existing systems.  Both options are available with long-term watertightness warranties.  Either way, compare the long-term costs of these two options with the long-term costs of panel replacement.