Getting the Most from your Metal Roof

by Jonathan McGaha | April 30, 2014 12:00 am

The paint systems used are highly reflective, which reduces the heat load on the building interior. However, one of the biggest benefits to using Galvalume-coated metal roofing is its long service life. Properly designed, installed and maintained, this metal roofing will last 40 years and longer. This is far longer than most any other types of roofing material. So, what should one consider to ensure his roof will provide the longest service life possible? Three things have to be considered-design, installation and maintenance.

Design

While designers typically do a good job with the layout and overall design of a building, there are some things that could be added and/or changed in the specifications that may prevent issues often encountered during roof inspections. Specify long-life fasteners for all exposed fastener locations.Standard carbon steel fasteners, even though they may be painted, will not last as long as the roof panels. The exposed fasteners will start to rust and transfer that rust to the roof surface. Eventually, this rust will perforate the roof panels and shorten the roof’s service life.

Another change involves roof curbs. Instead of having the HVAC contractor provide the curbs for rooftop units, have the roofing contractor supply and install them. When required to supply roof curbs oftentimes HVAC contractors will provide curbs made from G-60 galvanized material and fabricated for use on a BUR roof. These curbs will not last as long as the roof and will not allow the water to properly drain. A proper curb should be made from welded aluminum; be shingled into the roof (under the roof panels on the high side and on top of the roof panels on the low side); and provide minimum clearances to allow for proper water drainage.

A similar issue is allowing HVAC and plumbing contractors to supply their own roof jacks for flue pipes and plumbing pipes. The galvanized roof jacks typically used by HVAC contractors for flue pipes and the residential style jacks sometimes used by plumbers will not last as long as the roof panels. Again, have the roofing contractor supply and install all roof jacks.

In fact, the specifications should dictate all roof penetrations should be performed by the roofing contractor, or in instances such as lightning protection equipment, he should review the location, methods and installation of the penetrations. He is the expert at installing the roof and he is the one that will get the call if the roof leaks. All roof penetrations should be considered during roof design, and some should specify the required installation process. This will prevent penetrations.

When designers incorporate unusual geometry into a roof, care should be taken to ensure the detail can be installed in a long-term weathertight manner. This often requires a special welded aluminum fixture. However, if this is not covered in the specifications, the contractor will probably not spend the money for the aluminum fixture and instead try to install the detail with trim.

Additionally, specifications should provide for protection of the roof from corrosion due to dissimilar metals, which causes galvanic corrosion. The most common scenarios include copper lightning protection equipment, treated wood and condensate from rooftop AC units. It should be noted that copper or other dissimilar materials do not have to be in actual contact with the roof. Water dripping off of these materials onto the roof can cause corrosion. This is what is happening with AC condensate. The water running through the copper tubing of the AC unit contains dissolved copper ions and causes premature corrosion of the roof surface as it runs down slope to the eave.

Installation

One of the best things a roofing contractor can do is become familiar with the manufacturer’s details for the product that he is installing. Most manufacturers offer training classes for various roof systems. They can help contractors learn to recognize potential issues when bidding a project so that they can plan for special fixtures and/or additional labor to handle difficult details.

A common issue is contractors not understanding the best way to flash a valley that terminates short of the eave. This is often referred to as a “dead valley.” Dead valleys require the roof panel adjacent to the termination point of the valley have an end lap at this point to allow the valley trim to be shingled into the roof.

Oftentimes, roofing contractors fail to consider the thermal movement of SSRs. As the metal heats up or cools down, it expands or contracts. While manufacturers design roof systems to allow for this thermal movement, the roofing contractor must consider this movement as he is installing a roof. Some things to watch for include pinning the roof panels to the substructure at both the eave and ridge; cutting an oval hole in the roof at pipe penetrations so the roof panel does not foul the pipe during thermal movement; and consider how flashing will react to thermal movement.

On long buildings, ridge flash may require an expansion joint every 100 feet or so. Ridge flashing is typically designed to flex as the roof expands and contracts, but the ridge flashing will also expand and contract longitudinally and may cause lap fasteners to back out if expansion joints are not incorporated. Another issue with ridge flash is how it is often sealed to parapet walls. Many contractors try to surface caulk the ridge flash to the parapet wall. This never works because the ridge flash flexes and breaks the caulk seal. Always use a flexible membrane to allow the ridge flash to flex without losing the weathertight seal.

Maintenance

Metal roofs are low-maintenance, but they are not no-maintenance. To help keep the roof in top condition and maximize its life, watch for the following: don’t let anyone put things like antennae or satellite dishes on the roof without a proper way of attaching them. The best way is to use S-5! roof clamps, which will allow you to attach things to your roof without causing leaks or corrosion.

Finally, keep the roof clean. Regularly remove leaves, tree limbs and other debris from gutters, valleys or anywhere else it may collect. Anything that holds moisture to your roof’s surface for long periods of time will reduce its life.

The bottom line is this: If those involved in the design, installation and maintenance of a Galvalume-coated metal roof will consider that it should last at least 40 years and proceed accordingly, there is a very good chance the roof will be the only one needed for the life of the building.

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Ken Buchinger is the general manager of technical servicesfor MBCI, Houston. He has been instrumental in developing weathertightness warranties, erector training programs and research and development certifications. The statements and opinions expressed herein are solely those of the author and do not constitute official statements or positions of MBCI or its affiliates. For more information, visit www.mbci.com[1].

Source URL: https://www.metalarchitecture.com/articles/getting-the-most-from-your-metal-roof/

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