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Standard Testing For Metal Roofing – Part 2: Air and Water Resistance

Posted on August 7, 2018 by Jason Allen

In a prior post, we discussed the importance of independent (i.e. third party) standardized testing as a means of verifying the performance of metal roofing, and specifically looked at structural and wind uplift performance. In this post, we will similarly look at testing standards but focus on metal roofing tested for air leakage and water penetration.

Air Leakage and ASTM E1680

Keeping air from passing through a building system from the exterior to the interior (i.e. drafts) is a fundamental role of any building envelope system, including roofing. It is also important in controlling the flow of harmful airborne moisture into a roof assembly. Hence, testing a roofing panel for its ability to control air leakage is critical to the long-term success of the roofing system, and ultimately, the building.

ASTM E1680 “Standard Test Method for Rate of Air Leakage Through Exterior Metal Roof Panel Systems” is used to determine “the resistance of exterior metal roof panel systems to air infiltration resulting from either positive or negative air pressure differences”. It is a standard procedure for “determining air leakage characteristics under specified air pressure differences”. The test is applicable to the field portion of any roof area including panel side laps and structural connections but not at openings, the roof perimeter, or any other details. The test is also based on constant temperature and humidity conditions across the roofing specimen being tested to eliminate any variation due to those influences.

The standard test procedure consists of “sealing and fixing a test specimen into or against one face of an air chamber, supplying air to or exhausting air from the chamber at the rate required to maintain the specified test pressure difference across the specimen, and measuring the resultant air flow through the specimen”. Basically, the test is meant to reveal the ability of the selected roofing panel to resist the difference in air pressure between the two sides and thus demonstrate its air tightness.

The beauty of this standardized test is that different metal roofing products can be tested under the same conditions and compared. The standard calls for a pressure differential between the two sides of positive and negative 1.57 foot pounds of pressure per square foot of panel (75 paschals of pressure) and can be tested in the negative pressure mode alone if the roof slope is less than 30 degrees from horizontal.

MBCI’s metal roofing products are tested to confirm an air tight and water-resistant roof.

Water Penetration and ASTM E1646

In addition to air leakage, water leakage in roofing systems is obviously not desired. To test the performance of metal roofing products in this regard, ASTM E1646 titled “Standard Test Method for Water Penetration of Exterior Metal Roof Panel Systems by Uniform Static Air Pressure Difference” is the norm. This standard laboratory test is not based solely on free running water, but on water “applied to the outdoor face simultaneously with a static air pressure at the outdoor face higher than the pressure at the indoor face, that is, positive pressure”. This pressurized testing is intended to simulate wind-driven rain and flowing water that can build a head as it drains. The test measures the water-resisting properties of the roofing in the field of the roof panels including panel side laps and structural connections. Just like air testing, it does not include leakage at openings, perimeters, or other roofing detail areas.

The test method itself consists of “sealing and fixing the test specimen into or against one face of a test chamber, supplying air to or exhausting air from the chamber at the rate required to maintain the test pressure difference across the specimen, while spraying water onto the outdoor face of the specimen at the required rate and observing any water leakage”. Hence, it requires the air and water to be supplied simultaneously and for the testers to observe and document the rate of water leakage under the test conditions.

The test parameters typically require at least 20 gallons of water per hour (gal/hr) overall with between 4 – 10 gal/hr in any quarter section of the tested specimen, all at specified air pressure differentials. Given that this is a fairly stringent test, it is fair to say that metal roofing that holds up under these test conditions will likely perform well under most weather conditions when installed on a building. Typically, manufacturers have developed metal roofing products with seaming and connection methods that allow them to pass this test with virtually no observable water penetration.

To find out more about the tested results of metal roofing products you may be considering, contact your local MBCI representative or see the MBCI website and select the “testing” tab under a selected product.

Combatting Thermal Bridging with Insulated Metal Panels

Posted on March 23, 2017 by MBCI

When using compressible insulation, say for instance fiberglass batt, consideration must be given to how that insulation is going to be deployed in the actual wall or roof. For instance, installers might place the insulation across the framing members and then smash it down with the cladding and run a screw through to the underlying structure. The problem here is that the insulation is rated with some R-value—and that R-value is determined by an ASTM procedure that also determines what its tested density is. So in essence, it’s ‘fluffy’ insulation.

One manufacturer’s insulation, however, might be thicker than another’s. The contractor is buying an R-value, not a density or a thickness. The insulation is tested to that R-value at whatever thickness and density¹ is needed to achieve it. Let’s say R-19 fiberglass batt is specified, but then it is put in an assembly and smashed down flat… now it’s not R-19 anymore; it’s now R-something else. That’s a thermal bridge—when the insulation’s R-value has been compromised.

Manufacturers have the ability to run long length panels that minimize the number of end joints. This continuity provides significant advantages over traditional insulated materials when designing for energy efficiency. This image illustrates the difference between fiberglass batting made discontinuous by compression between panel and framing members and the continuous insulation provided by insulated metal panels.

Unfortunately, thermal bridging is almost impossible to eliminate. In the example above, another choice might be to put it between studs. Except in this situation, the studs break the insulation. While it’s not pinched, the studs are separating it. Whether the studs are metal or wood, in either case it’s still a significant thermal short circuit or a thermal bridge.

Even with the highest quality insulation systems—insulated metal panels, for example—a joint is required. Building is not possible without putting neighboring panels together. Therefore, insulation is discontinuous. While it’s impossible to avoid thermal bridging, there are two requirements to ensure the building performs the way it needs to perform.

Thermal bridging must be mitigated. In other words, the designer or installer has to try to eliminate as much of it as possible.
If thermal bridging is unavoidable, it must be accounted for in some fashion, which usually means putting more insulation somewhere to make up the difference. This is called a “trade-off” and is allowed by most building energy efficiency codes.²

Why Insulated Metal Panels?

Insulated metal panels then are the best bet, because although the joint is a thermal bridge, in effect, it is not nearly as impactful as breaking a line of fiberglass with a stud or smashing the fiberglass between the panel and a framing member. In the illustration below, R-value doesn’t just vary at that point where the panel and the stud meet. The entire insulation line gets smashed and one would have to go some distance from the stud before the insulation returns to its normal, fluffy thickness. These issues need to be mitigated and accounted for.

Continuous insulation is critically important to an efficient envelope design. Insulated metal panels, with their side laps designed for concealed fasteners, eliminate the possibility of gaps in the insulation and thermal bridges. Continuous insulation is important because thermal bridges and discontinuities introduced by compressing non-rigid insulations cause the in-place R-Value of the assembly to be less than the tested R-Value of the insulation used. This effect has become a focus in newer energy efficiency codes such as ASHRAE 90.1 and IECC.

Manufacturers such as MBCI and Metl-Span publish insulated metal panels as U-factors because the joint is tested as part of the assembly (both mitigating and accounting for the aforementioned issues). These values can be found on product data sheets and technical bulletins, such as Metl-Span’s Insulation Values technical bulletin, published January 2017.

References

ASTM C 665 – 12, Standard Specification for Mineral-Fiber Blanket Thermal Insulation for Light Frame Construction and Manufactured Housing, Table 1, Footnote c.
ASHRAE 90.1 – 13, Energy Standard for Buildings Except Low-Ride Residential Buildings, Section 5.6
High Performance Green Building Products – INSMP2A (CEU)

MBCI Welcomes Insurance Institute of Building & Home Safety to Witness In-House Testing

Posted on May 11, 2015 by MBCI

To ensure our products perform as expected, MBCI conducts a variety of tests at our onsite laboratory in Houston, Texas. On April 16, MBCI and our parent company, NCI Building Systems, welcomed several researchers from the Insurance Institute of Building and Home Safety (IBHS) to our Houston headquarters to witness ASTM E1592 testing on MBCI’s standing seam roof panel Double-Lok. This test is designed to evaluate the structural performance of a standing seam roof system under uplift loading experienced by roofs during wind events.

IBHS conducts research to improve loss prevention-related design practices and better understand the risks of insuring buildings and homes. IBHS’s facilities include a full-scale wind tunnel in South Carolina which recently tested a 30’ wide, 50’ long building by our sister company, Ceco Building Systems, using the same standing seam roof system used in the E 1592 test. IBHS’s researchers joined our testing to observe how manufacturers test their own products so they may develop design-related loss prevention strategies which can help reduce insurance costs for consumers of metal roofing.

NCI’s Senior Research and Development Engineer Mark Detwiler, who was present at the testing, said “[IBHS] indicated that the test they witnessed reinforced that the industry rigorously tests their roof systems. They also noted that the failure mode they witnessed was consistent with what they have seen in their loss investigations, meaning that the test yields realistic, predictable results.”

Learn more about Double-Lok, ASTM E1592 testing and IBHS and their research efforts.

Part 1 – The Importance of Consensus in Building Standards

Posted on March 3, 2015 by MBCI

Most people understand the purpose of a building code: To ensure the safety of the occupants and to establish the minimum accepted performance level of the building and its systems. Fewer people understand that because building codes are adopted into law by a governing body, technically referred to as an Authority Having Jurisdiction or AHJ, they are an in fact an extension of the law or ordinance that brings them into effect. Knowing that, you should not be surprised to learn that like laws, building codes in America can’t just be arbitrarily made up by somebody having the authority and know-how to do so. Instead, they must have gone through some type of consensus process in which all affected entities or their representatives have the opportunity to participate. This concept, called Due Process of Law, is central to many governmental charters such as the Magna Carta and The Constitution of the United States of America and is designed to ensure that a person’s individual rights are not unfairly taken away.

Under the US Constitution, laws are written by Congress and interpreted by judges. Members of Congress are elected by their constituents and judges are either appointed by elected officials or elected themselves. Similarly, building codes are written by consensus bodies, like the International Code Council or ICC, and interpreted by Building Officials, who are generally appointed by elected officials. The code development process used by ICC is one where any interested member of the public can participate and is guaranteed a forum to propose changes and comment on the proposed changes submitted by others using a system governed by Roberts Rules of Order. After discussion and debate, the code committee votes on the individual proposals and those that pass are incorporated into the code, guaranteeing due process. (Actually, it’s quite a bit more complicated than this but for purposes of this blog, let’s just leave it at that.)

However, building codes commonly do not actually spell out all of the requirements for buildings and building systems. More and more, the code will delegate low-level detailed requirements to a different type of document called a standard, and then brings the requirements contained within by referencing the standard in the code by name. Likewise, these standards then must also be developed through a consensus process administered by an adequate standard development body. But because all standard development bodies are structured a little differently, it is not realistic to mandate that consensus process directly. Instead, another independent body called The American National Standards Institute or ANSI, certifies standard development bodies as having a sufficient consensus processes to be deemed as meeting the incorporating code requirements for due process. Examples of these bodies are the American Society of Civil Engineers (ASCE) who develop ASCE 7, the document that determines the minimum load requirements for buildings; the American Society of Testing and Materials (ASTM) a group widely known for developing material and testing specifications for general use; and the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE), who develops ASHRAE 90.1, the document that spells out the minimum building energy efficiency requirements. If you are an architect or engineer, all of these acronyms should sound very familiar to you.

Another acronym that you are probably familiar with is LEED, which stands for Leadership in Energy and Environmental Design. It is developed and maintained by the US Green Building Council (USGBC) and is the premier green building program in the world. Interestingly though, the development landscape changes drastically when it comes to green construction programs like LEED. You see, the USGBC is not an ANSI accredited standard developer and thus LEED is not an actual official standard, hence the use of the word “program”. How then is it possible that USGBC can have so much say in how buildings, particularly publicly owned buildings, get built? The answer is that they get around this limitation by structuring LEED as a voluntary program and then lobbying the potential owners of buildings, like the US and state governments, into using their program by executive order rather than legislating the requirement directly. If you’ve watched TV at all in the last year, particularly with respect to immigration reform, you know how controversial this approach can be. Nevertheless, it is perfectly legal in this context.

This really has not been a significant issue to date because LEED does have a consensus process (albeit not an ANSI accredited one) and LEED credit requirements have been fairly uncontroversial in past versions. However, LEED v4, the latest generation of the wildly popular green building program, changed all of that by adding credits that are less about design and functionality of the building and more about transparency with respect to building product ingredients to ensure occupant health and comfort. Let’s be clear: Most reasonable people, including building product manufacturers, don’t have a problem with increased transparency and want more occupant comfort and health. But it is how LEED defines “transparency” in version 4 has many people up in arms and they point to the hypocrisy of developing a definition to the word “transparency” during a closed-door meeting with no manufacturers at the table as what is wrong with green building as it exists today. My next blog will explore that concept further.