Photo courtesy of Met-Tile
Metal roofing has grown in popularity in both new construction and remedial roofing applications. Advancements in material technology and application procedures have been instrumental in increasing market share. Contemporary metal roof systems are much more reliable than their early predecessors. Today's systems have the capacity to offer long-term service life; in fact, some of them may last up to 50 years with proper maintenance and repairs.

The elements required for establishing proper roof maintenance guidelines on metal roof systems are similar to maintenance conducted on conventional systems. The roofing contractor should have knowledge of different metal roof systems and their application procedures. Familiarity with these systems can help identify typical problem areas that will require routine maintenance

Identifying Roof Leaks

The goal of any roof maintenance program should be to extend the service life of the existing roof system by eliminating and correcting all problem areas at their initial stages. The most common problem associated with metal roof systems is roof leaks. Metal roof leaks are often a result of improper construction methods. For example, leaving roof penetrations unprotected or omitting the required sealants at joints and penetrations will always lead to leaks. These are items that are easily identified and corrected, as are most metal roof problems.

In fact, metal roof leaks can typically be traced to four common application errors. Roofing contractors that are aware of these items on service calls for metal roof systems can be of great benefit to the building owner. When answering these service calls, the first four areas for which the repairman should look are:

Omission or misplacement of the required bar and caulking-type sealants in the longitudinal roofing seam cavities

Failure to install the extra strip of sealant at the four-way panel laps and at the eave connections

Failure to install tape sealant under the screw heads

Not caulking between the extra trim and the underside of the roof panels

The presence of sealants at the required locations can be detected through the use of a special "feeler" tool. The tool should be fabricated to a thin dimension of approximately 0.0005 inch so that it fits in the roofing seam. If it is determined that sealant is not applied at these points, remedial work may require removal of the panel, application of the proper sealant and reinstallation of the panel.

Of course, not all roof leaks can be attributed to improper workmanship. Some problems occur due to inadequate design details. A case in point: waterproofing of standing seam roof systems with trapezoidal seams is highly dependent on the proper installation of the closure strips that are applied at the corrugated eaves. If end closures are not designed for application at these points, leaks will occur from overflowing gutters or ice damns. The applied sealant should be thoroughly inspected for openings if end closures are applied.

If the leaks are not occurring at these points, the repairman should investigate the other most common points of concern. On metal roof systems, leaks are also susceptible at open seams and penetrations. Improper terminations of metal at vertical locations, particularly at interfaces with other types of materials (i.e. wall masonry) or at ridge vents, are other common points of moisture infiltration.

Common Metal Repair Procedures

Proper repairs can be completed by using the appropriate materials for the existing metal surface. Most metal system manufacturers have repair procedures that should be followed. Some general repair procedures are listed below.

One common point of moisture infiltration in metal roof systems is at the openings created by missing or corroded fasteners. To properly repair these areas, remove and replace all severely corroded as well as missing fasteners with an acceptable corrosion-resistant type fastener. Replace all severely weathered washers with new butyl rubber washers. Trowel or caulk exposed fasteners with proper sealant by totally covering the fastener heads.

Openings in the metal surface also require proper attention. Repair all splits, holes or protrusions in the metal surface using proper metal sealant and repair material. This is accomplished by following the steps provided here. First, thoroughly clean the metal surface so that it is free of all dirt and debris. The surface must be completely dry prior to material application. Trowel-apply an approved metal adhesive approximately 1/2 inch thick over the cracked or split areas. Set one layer of a metal fiber membrane over the affected area in an even application of adhesive. Finally, trowel-apply the adhesive over the metal fiber membrane in uniform even coatings.

The structural integrity of the metal can be compromised by excessive rust and pitting of the metal surface. Repairs and/or replacement of the metal surface may be required depending on the severity of the surface corrosion. Remove and replace all metal panels that are severely corroded or deteriorated by weather to the point that they may pose a safety threat. Typically, this type of corrosion can be identified by several metal surface openings and extensive rust in a concentrated area. Best practice methods require replacement of metal panels in areas of doubt regarding the severity of the corrosion. In these cases it is best to err on the side of safety.

Metal surfaces that exhibit minor surface rust can be treated with remedial repairs. The surface rust must be removed by hand tool cleaning, which may include sanding, scraping or removal with a wire brush. Once the rust is substantially eliminated from the metal surface, an application of an approved primer or rust inhibitor should be set over the affected surface area.

The most common repair and maintenance application on metal roof systems is the application of a coating. Coatings can be applied for a number of reasons, such as to provide weatherproofing protection, to provide reflection or emissivity or for esthetic purposes. When they are properly applied, metal coatings can extend the service life of the metal system. However, there are varying degrees of coatings on the market today and the roofing contractor should conduct the necessary research to determine the best types of coating for the different types of metal surfaces. Metal coating application requires proper preparation. All of the aforementioned repairs should be completed prior to the final coating application. The metal surface should be thoroughly cleansed of all loose rust, mill surface and paint, as well as all loose dirt and contaminants. Clean the surface by using power tools such as power sanders, wire brushers or grinders. A more common cleaning procedure is the use of high-pressure water blasting at not less than 2,000 psi.

Once the metal preparation procedures are completed, and the metal surface is completely dry, the coating application can begin. Apply an approved metal coating over the metal surface at an application rate in accordance with the coating manufacturer's requirements. Most coating manufacturers provide warranties based on the coating thickness. The proper applied mil thickness is required to achieve the warranty levels. The coating should be applied in an even application. The metal coating can be applied using approved spray equipment, brushes or rollers.