Posted by McElroy Metal ● Oct 23, 2019 8:00:00 AM

Specifying a Commercial Metal Roof

Metal roofing has been a popular product for commercial buildings for decades. In fact, nationally about 1/3 of all commercial buildings have metal roofs and metal roofing is even more prevalent in coastal areas. Extreme weather conditions such as tropical storms and hurricanes have led many municipalities to require metal roofing because of its superior wind uplift performance.

Standing Seam Roofing System on Commercial Building

When planning to specify a commercial metal roof, there are several factors that should be considered. Architects commonly focus on topics like: Local building codes, building geometry, paint system, desired aesthetics, connection method, underlayments, budget, contractor experience and weather tightness warranties.

Local Building Codes

Local building codes play an important role in the product ultimately selected for commercial metal roofing. Codes can address everything from wind speed requirements to solar reflectivity. The best course of action is to be proactive with your code enforcement agency and contact them before your project begins to learn about the specific requirements. After you have an idea of the local requirements for your site, you can then partner with your metal panel manufacturer to identify the best solution and products for your project.

Check our downloads section and the submittals listing for examples of roofing specifications like the 238T Standing Seam Metal Roof System.

 

Building Geometry

When selecting product for a commercial metal roof, the building geometry plays an important role. Slope or roof pitch is one of the first major considerations. The slope of the roof should be a minimum of ¼:12 in order to utilize a metal roof according to the International Building Code; however, many manufacturers have minimum slope limits that exceed those found in the IBC. You will find that lower sloped buildings have fewer panel selections than those with steeper slopes. When slopes of ½:12 or greater are present, a wider range of panel options are available. Also due to their configuration and difficulty to make weather tight, trapezoidal panels are typically not preferred for applications with long panel lengths and valleys. Another key consideration regarding your building geometry is the length of the panel run. As panels heat and cool with the sun and seasons, they expand and contract. This expansion and contraction can be considered negligible for short panels runs of 40 feet or less; but for longer length panels, a standing seam system capable of accommodating thermal expansion is necessary. For reasons like this, most design professionals find it helpful to reach out to a metal panel manufacturer to discuss their project specifics in order to select the best panel in regard to both performance and cost. If we can ever help in this discussion, feel free to use our “contact us” form here

Paint System

Specifying a long-life paint system for a metal roof is critical because the right paint will last the life of the roof and still look great.

Kynar 500® is a fluoropolymer (polyvinylidene fluoride or PVDF) resin that is used by leading paint manufacturers to create long-life coatings for many end uses including metal roofing and siding.

A key advantage of Kynar 500® is its superior resistance to chalk and fade. Fading is caused by the breakdown in pigment, usually from ultraviolet light. Chalking is caused by the breakdown of the paint’s resin into a white, chalk like substance. All paints will eventually chalk and fade; however, Kynar 500® coatings outperform other paints such as polyester or silicone modified polyester based paints by far.

In the picture below, you can see the difference between a section of a roof that has been coated with Kynar 500 and sections that were coated with a Siliconized Modified Polyester (SMP) paint. All the sections looked the same on the day they were painted and installed. Over the course of just eight years (a small portion of the life of a metal roof) the Kynar 500 section retained its vibrancy and didn’t chalk or fade.

Check out this related post Metal Roof Paint Systems: Kynar 500 vs. SMP.

kynar 500 comparison

Desired Aesthetics

In many commercial metal roof applications, the roof slope is low enough that the panels are not visible when looking at the building’s facade. In those cases, aesthetics rarely enter into the decision making process and unpainted roof panels are often used in widths of 24”. Wider panels offer significant labor savings with no adverse weather tight performance. However, in higher slope situations where aesthetics play a key role, panel widths of 16-18” are more common, as are painted finishes. Aesthetic considerations play a key role in the early stages of both product selection and budget analysis.

Connection Method

There are two primary styles of metal roofing : standing seam systems and exposed fastener systems. The connection method used affects the system’s cost, life expectancy and maintenance requirements.

McElroy%20Metal%20Maxima%20Striated%20Standing%20Seam%20System%20Rendering

Standing seam systems join the edges of two adjacent panels in a single-fold, double-fold, or snap-fit perpendicular to the roof plane. Standing seam panels are also referred to as as concealed fastener panels because the roofs have no exposed metal fasteners. Instead they use a concealed clip for attachment to the substructural material.

Conversely, exposed fastener panels are fastened to the building through the face of the metal roofing panel directly to the framing or roof deck underneath. Learn more about commercial metal roofing panels here.

Underlayments

Underlayments are designed to provide a secondary barrier of weather protection for a building's interior. During construction, an underlayment helps keep the interior of the structure dry. Once the roof construction is finished, if for some reason the metal roofing above is compromised, an underlayment also helps to shed water away from the conditioned building interior. In essence, underlayments protect the structure and anything stored directly below the roof both during and after construction.

Synthetic underlayment offers greater longevity than its paper-based counterpart and is the best underlayment option available. Metal roofing systems are generally in direct sunlight and can become quite warm, remember to always specify a “high-temp” underlayment when working with metal roofing.

For more information, you might check out our earlier blog on underlayments by clicking here.

Contractor Experience

When properly installed, metal roofs can perform for 50 years or more; consequently, they represent an outstanding option for commercial metal roofs. With that said, in order to gain optimum performance, proper installation is absolutely critical. For these reasons, most experienced specifiers have a section in their specifications regarding contractor experience. See example below:

1.05 QUALITY ASSURANCE
A. Installer Qualifications: Installer experienced in performing work of this section who has specialized in the installation of work similar to that required for this project for a period of five years with documented proof of three projects with comparable size and complexity.

For more tips on creating solid specifications, be sure to visit the Downloads section of our website and click on the "Specifications" tab to find editable copies of master spec documents for all of our panel products.

Commercial Roofing Materials

The most common metals used for roofing include steel, aluminum and copper. It is very important for specifiers to consider cost, available testing, warranties and project specifics in their material choices. Regarding cost, copper is typically the most expensive with aluminum products in the middle and steel options (both galvanized and galvalume) coming in on the lower end of the price point continuum.

Depending on the final building application, specifiers often include compliance requirements to industry standardized tests addressing topics such as wind up lift values, fire testing and air and water testing in their specifications. It’s critically important that specifiers check carefully to ensure their preferred material has been tested for (and meets) the desired testing criteria. It’s not unusual for some materials such as steel to have far more available testing than products such as aluminum and copper.

Project specifics can also play an important role in the material selected and specified. Coastal environments are a good example of this. Some specifiers favor aluminum in these applications due to their ability to withstand constant salt spray. But when extreme wind values are demanded, galvalume products may become more favored due to higher uplift values. Panel length is yet another consideration. By nature aluminum expands and contracts at a much greater ratio than steel; consequently for projects with long panel lengths, galvalume material may be better suited. Ultimately, material choice is another great topic to discuss with several manufacturers to ensure you’re making the best possible choice for your project.

Weather tightness warranties

Weather tightness warranties offer specifiers and owners an assurance that the building will remain leak free for a period of years. Most reputable manufacturers offer these types of warranties on standing seam panels only for periods ranging from 5-20 years.

As a specifier, it is critically important to word your specification to include the limit of liability expected. When specifications include verbiage such as manufacturers “standard” weather tightness warranty, the coverage is typically minimal and won’t come close to replacing the roof should failure occur. For this reason, if you’re considering including a weather tightness warranty in project specifications, be sure to discuss your expectations for liability limits with all manufacturers included in the specification and ensure your specification is very clear on the desired liability limit.

It’s also important to understand that properly installed metal roofing systems don’t leak; leaks occur when contractors have not taken all the necessary steps to properly seal the system. So in essence, a weather tightness warranty makes the manufacturer responsible for the contractor’s installation. As a result they do provide some element of reassurance since reputable manufacturers often maintain a higher level of involvement with approval of details and inspections during installation; however, that simply can’t be assumed. A better course of action is to save the additional cost of the weather tightness warranty and instead write your specification to require strong contractor experience with projects of similar size and scope as mentioned earlier.

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Learn everything you need to know about commercial metal roofing.

About McElroy Metal

Since 1963, McElroy Metal has served the construction industry with quality products and excellent customer service. The family-owned components manufacturer is headquartered in Bossier City, La., and has 13 manufacturing facilities across the United States. Quality, service and performance have been the cornerstone of McElroy Metal’s business philosophy and have contributed to the success of the company through the years. As a preferred service provider, these values will continue to be at the forefront of McElroy Metal’s model along with a strong focus on the customer.

Topics: Metal Roofing, Coatings, Standing Seam Systems, Concealed Fastener Panels, Commercial, 138T and 238T

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