Penetrating a Metal Roof: Specifying leak-free assemblies

by Katie Daniel | January 9, 2018 2:16 pm

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by Rodger Russ
Once a building owner invests in the longevity promised by a standing-seam metal roof, there will be little patience for leaks. A standing-seam roof—one of the longest-lasting options available—is often specified because of its durability and minimal maintenance requirements. Some metal assemblies include a 360-degree double-lock seam to create a truly monolithic watertight surface. Alas,
a hole is a hole.

Roof penetrations are the number-one source of leaks in these roofs, and even a single poorly installed fastener can lead to millions of dollars in damage to the inventory or equipment below. A detailed specification encompassing several best practices for penetrating a standing-seam metal roof helps protect a building owner from the havoc of leaks.

Considerations for common roof penetrations
While common sense dictates cutting holes in any roof should be avoided whenever possible, there are five typical reasons to penetrate a standing-seam metal assembly. These include:

• ventilation piping;
• air circulation exhaust fans;
• HVAC equipment and associated ductwork;
• solar applications; and
• daylighting.

Ventilation piping
Leaks related to ventilation piping penetrations are relatively easy for an experienced professional to remedy, but it is important to thoughtfully specify them, given the implications they have on the roof’s weathertight warranty.

One tactic is to specify the penetrations be performed by the roof installer, rather than the mechanical contractor. This is a deviation from common practice, but can be an important step in ensuring they are done properly. Not all mechanical contractors are educated in how to produce a weathertight seal around the pipe they put through a metal roof. Many do not carry fasteners or sealants required to ensure a proper installation. Further, the responsibility (and thus liability) for the flashing falls typically on the roofing contractor.

It is also critical to require the penetrations be performed according to the manufacturer’s guidelines to protect warranty compliance. The roofing contractor is usually well-versed in installation details required by manufacturers; this includes ensuring the metal roof is permitted to expand and contract as needed per the system requirements while not compromising the weathertight integrity of the penetration flashing. Specifications should require the roof installer be responsible for fitting all penetration flashings to ensure trained personnel are weatherproofing them. If this is left to others, improper methods might be employed, resulting in leaks and damage not covered by the manufacturer’s warranty.

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Air circulation exhaust fans
There are two primary focal points when specifying how roofs should be penetrated in order to accommodate exhaust fans while avoiding leaks—the curb and adequate secondary structural supports.

Ensuring the former can integrate with and be supported by the metal assembly is the challenge, because, ultimately, the curb—not the fan—is key to keeping a roof weathertight. It is imperative the specifier research the metal roof basis of design in any specification and approved substitutions to ensure the manufacturer has curbs that integrate with the specified assembly to provide a weathertight installation. This often eliminates several manufacturers, as not all have approved curbs and details for this purpose. If left up to others to determine, the least expensive conventional curbs are often installed, jeopardizing the warranty, or worse yet, the weathertight integrity of the roof system.

Typically, the curbs need to be supported by systems not initially designed as part of the building structure. These secondary structural members tie into the structure and support the weight of the curb and exhaust fan, as well as allow for an attachment point for the new curb. Without them, the roof panels may start to deflect, creating a potential for leaks. Lack of proper secondary structural support is one of the most common defects in curb installation.

Repairing leaks caused by air circulation and exhaust fans can be much more challenging than fixing penetrations for ventilation piping. These types of repairs may require multiple trades, including electricians. In some cases, it must not only include replacing the damaged curb, but also the structural members.

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HVAC equipment
HVAC-related penetrations can range from being fairly minimal to extensive, depending on the building design and its heating and cooling requirements. Irrespective of the scope, it is critical that each penetration is correctly installed.

There are a couple of different approaches to installing HVAC equipment on a standing-seam metal roof. In applications where the curb for the HVAC unit encompasses all potential penetrations, the ductwork is inside the curb. The size of this unit is typically limited to 907 kg (2000 lb) or less and 1.2 x 1.8 m (4 x 6 ft) in size. These can still easily divert water around the base.

In applications requiring multiple curbs and penetrations for ductwork and related electrical requirements, larger HVAC units are often installed on racks or steel structures, as their size and weight prohibit employing a typical curb. This type of installation suspends the equipment 0.6 to 0.91 m (2 to 3 ft) above the roof surface. Electrical connections and ductwork, along with the structural supports (e.g. round pipes or wide flange beams), are then flashed accordingly.

Repairs for large HVAC units can be very challenging and expensive, often requiring the use of a crane. Therefore, it is critical to be thoughtful in how they are specified. In any case, best practices include specifying the curb be supplied by the roofing manufacturer and the work be completed by the roofing contractor.

Solar applications
Standing-seam metal roofs are strong options when building designs include solar panels. The preferred approach to minimize leaks is one that specifies the panels be attached to the roof using manufacturer-approved clips. These are designed to attach to roof panel seams with set screws, eliminating the need for fasteners or additional penetrations.

Mounting solar panel racking systems to the building’s support structures through the roof requires minimal penetrations, and leaks are often the result of improper installation of these supports or electrical work versus a problem with the panels themselves. These leaks tend to be fairly easy to repair. The same common practices utilized with suspended HVAC equipment should be employed and properly specified. Additionally, communication between the panel system installer and roofing contractor is critical.

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Daylighting
More and more building owners are opting for daylighting as facility managers are becoming aware of benefits like saved energy costs and increased employee productivity. Further, the International Energy Conservation Code (IECC) and American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) energy codes are mandating it. (Since standing-seam metal roofs are energy-efficient, they may help building owners apply for credits under the Leadership in Energy and Environmental Design [LEED] program for certain projects.)

Historically, either lite panels (translucent fiberglass panels with the same profile as the metal panels) or skylights and roof curbs were the most common daylighting solutions, but both created challenges in maintaining a weathertight assembly. For example, the warrantable service life for fiberglass is limited to 10 years—lite panels then become brittle and a significant safety hazard.

Skylights with curbs face similar challenges as roof-mounted exhaust fans, including possible panel deflection if proper secondary supports are not used. Additionally, when the specification is open or ambiguous, curbs designed for conventional built-up roofs (BURs) are commonly used. This is problematic because using improper curbs often lead to recurring leaks.

The good news is installing a daylighting system is no longer an open invitation for roof leaks. Recent innovations include seam-integrated or self-curbing systems that support prismatic domes. These systems use a design that has a diverter in the rear and a dome over the seam-integrated extruded aluminum rails to minimize leaks. This type of installation eliminates the need for secondary structural supports and moves the attachment point above the roof line to mitigate the chance for leaks.

Specifying a building employ a seam-integrated/self-curbing solution will help maintain a weathertight roof surface over the long term.

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General best practices
Regardless of why a roof needs to be penetrated, there are critical steps to execute with the manufacturer, prior to installation, to ensure quality work. Any time a standing-seam roof is penetrated, its weathertight warranty is in jeopardy. With some manufacturers offering coverage of up to 25 years, this is a considerable risk.

Adhering to these best practices is an important first step in not only protecting the building owner from roof leaks, but also ensuring the validity of the manufacturer’s warranty. When specifying a standing-seam metal roof, this author strongly suggests including these five steps:

1. Use only curbs fastened with an internal flange to significantly reduce the number of exposed roof penetrations.
Patch-style curbs can require more than 100 fasteners each. Considering there may be hundreds of curbs installed on a roof, the result is tens of thousands of penetrations and potential leaks. Often, even clean installation cannot overcome poor curb design in maintaining a weathertight roof.

2. Metal roof curbs must be supported by secondary structural members to prevent the panels from deflecting.
This direction is often overlooked, and the result is ponding water where fasteners connect the curb to the panel, which can cause separation. Once ponding occurs, leaks are not far behind.

3. Source any methods and components for penetrating the standing-seam metal roof directly from the manufacturer or per the manufacturer’s instructions.
Failure to include this instruction may result in the contractor opting for the lowest-cost solution, which jeopardizes the warranty. In fact, unapproved modifications and penetrations are the most frequent reason for nullification of standing-seam roof warranties.

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4. Confirm all professionals are certified and skilled at installing metal roofs, as there are distinct differences between metal and single-ply roofs.
One should never assume the trades are interchangeable.

5. Inspections by a qualified consultant or by the manufacturer are critical.
Whether there is a warranty or not, this is always a good idea to ensure the roof and penetrations were properly addressed.

By thoughtfully specifying how these roofs are penetrated, design/engineering professionals can help ensure building owners realize the full value of their roof systems. The keys to helping maintain a weathertight assembly and a valid warranty are simple. It comes down to minimizing the number of exposed fasteners as well as ensuring the methods and materials are supplied by the manufacturer and installed by the roofing contractor.

Millions of square feet of standing-seam metal roofs across the globe are long-standing and leak-free. Standing-seam metal roofs offer significant benefits over other options, especially in terms of minimizing maintenance and maximizing lifespan. From warehouses to data centers, these roofs are trusted to provide weathertight protection for critical infrastructure and inventory.

Rodger Russ is the North American sales manager for the roof division of Butler Manufacturing. He has more than 30 years of experience since starting in the sheet metal trade in Chicago. Russ has worked for multiple manufacturers in various roles, including product development, training, product and sales management, and consulting. In his role with Butler, he focuses on applying new solutions for the retrofit segment of the metal roofing market. Russ can be reached at editorial@butlermfg.com[7].

 

 

 

Source URL: https://www.constructionspecifier.com/penetrating-metal-roof-specifying-leak-free-assemblies/

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