International Energy Conservation Code Archives

Understanding LEED for Green Metal Buildings

Posted on May 21, 2019 by MBCI

Designing and constructing sustainable buildings has become a mainstream expectation of most building owners. Whether for reduced energy costs, higher returns on investment, or as an organizational philosophy, “green” building solutions are in demand. Perhaps the best known and most often cited program to achieve these goals is the US Green Building Council’s (USGBC’s) LEED^® rating system. While some may think that green buildings are more complicated and costly to build, that is not actually the case. This is especially true when metal building materials are used. In fact, metal buildings are an ideal and economical way to pursue sustainability goals and LEED certification. How? We break it down as follows:

The LEED^® Program

The LEED program has been in use since 1998 and is now used worldwide. It is a voluntary, point-based rating system that allows for independent review and certification at different levels. These levels include Certified (40-49 points), Silver (50-59 points), Gold (60-79 points), or Platinum (80 or more points). Since it allows for choices in which points are pursued, innovation and flexibility are entirely possible as long as specific performance criteria are met. It also encourages collaborative and integrative design, construction and operation of the building.

Points are organized into six basic categories, many of which can be addressed through metal building design and construction, as summarized below.

Location and Transportation: Metal buildings can be manufactured and delivered to virtually any location. That means they can support LEED criteria for being located near neighborhoods with diverse uses, available mass transit, bicycle trails, or other sustainable amenities. Metal building parking areas can also be designed to promote sustainable practices for green vehicles and reduced pavement. This all contributes toward obtaining LEED eligibility.

Sustainable Sites: Adding a building to any site will certainly impact the natural environment already there. Delivering portions of a pre-engineered metal building package in a sequence to arrive as needed means that the staging area on-site can be minimized—reducing site impacts. Additionally, using a “cool metal roof” has been shown to reduce “heat island” effects on the surrounding site and also qualify for LEED.

Water Efficiency: Any design that reduces or eliminates the need for irrigation of plantings and other outdoor water uses is preferred. Incorporating metal roofing with gutters and downspouts, as is commonly done on metal buildings, allows opportunities to capture rainwater for irrigation or other uses. It also helps control water run-off from the roof and assists with good storm water control.

Energy and Atmosphere: Metal buildings can truly shine in this category. Creating a well-insulated and air-sealed building enclosure is the most important and cost-effective step in creating an energy conserving building. A variety of insulation methods for metal building roof and wall systems are used to achieve this. Typically, metal building construction uses one or more layers of fiberglass insulation and liners combined with sealant and air barriers. Alternatively, insulated metal panels (IMPs) provide all of these layers in a single manufactured sandwich panel with impressive performance. Windows, skylights and translucent roof panels can provide natural daylight, allowing electric lighting to be dimmed or turned off. For buildings seeking to generate their own electricity, standing-seam metal roofing provides an ideal opportunity for the simplified installation of solar photovoltaic (PV) systems. Metal roofs generally provide a sustainable service life in excess of 40 years. This means they can outlast the PV array, thus avoiding costly roof replacements during most PV array lifespans.

Materials and Resources: Life Cycle Assessments (LCAs) are recognized by LEED as the most effective means to holistically assess the impacts that materials and processes have on the environment and on people. Fortunately, the Metal Building Manufacturer’s Association (MBMA) has collaborated with the Athena Sustainable Materials Institute and UL Environment to develop an industry-wide life cycle assessment report. There is also an Athena Impact Estimator that can help with providing LEED documentation. Metal buildings support exceptional environmental performance through the significant use of recycled steel and the reduced need for energy intensive concrete due to lighter weight buildings.

Indoor Environmental Quality: Most people spend much more time indoors than outside, which impacts human health. Therefore, LEED promotes or requires using materials that don’t contain or emit harmful substances. It also promotes design options for natural daylight, exterior views and acoustical control to promote psychological and emotional well-being. Metal buildings are routinely designed to readily incorporate components that help achieve these indoor qualities.

In addition, some LEED points are available for demonstrating innovation and addressing priorities within a geographic region.

Considering the qualities listed above, metal buildings clearly provide a prime opportunity to pursue LEED certification at any level. To find out more about the LEED rating system, visit https://new.usgbc.org/leed. To find out more about successfully designing and constructing metal buildings pursuing LEED certification, contact your local MBCI representative.

Reducing Peak Demand Costs with Cool Metal Roofs

Posted on May 9, 2017 by Candy McNamee

Among the many benefits offered by cool roofs—including a decrease in urban heat island effect or increased roof system longevity—perhaps the most significant is a reduction in peak demand energy usage which directly affects building expenses.

Peak demand is the highest point in the day at which a building draws electrical consumption. A facility’s monthly utility rates are largely determined by the power usage level at this time, so anything that can be done to drive usage down will significantly reduce utility costs. As evidenced by their test values, cool roofs are an effective way to decrease air conditioning loads during peak demand times.

Cool roof values are expressed in terms of solar reflectance and thermal emissivity. The combination of these values is used to determine how hot a surface will become by its ability to reflect solar energy and radiate heat away from itself. Cool roofsare capable of reflecting solar heat away from a building by more than 70 percent. In fact, the U.S. Environmental Protection Agency estimates that ENERGY STAR® qualified roofing products can lower roof surface temperatures by up to 50°F.

According to Jeff Steuben, executive director, and Carolyn Richter, communications manager, Cool Roof Rating Council (CRRC), in a recent Florida Roofing article, “Building occupants can experience improved comfort as compared to a conventional dark roof, as the building’s interior is subject to less thermal flux and stays cooler during warm seasons,” and, “Reduced indoor temperatures lead to energy savings from reduced cooling energy loads.”

Along these lines, contractors can also access a CRRC-provided listing of cool roof rebates, codes and voluntary cool roof programs at: www.coolroofs.org/resources/rebates-and-codes.

Cool Roofing Longevity

In addition to energy efficiency, cool metal roofs are known for extended durability and longevity, with most products offering a 40-year finish warranty.

In fact, a well-noted extensive study, Natural Exposure Testing in California, conducted by the Oak Ridge National Laboratory, found that pre-painted metal roofing maintained higher levels of reflectance, over a three-year period, due to its ability to shed particulate matter, as compared to conventional roofing materials. Further, pre-painted metal roofing has been found to retain 95 percent of its initial solar reflectance over this same three-year period.
Increasing performance and energy savings, solar reflective pigments in cool metal roofs offer higher total solar reflectance and thermal emittance, even in darker colors. With cool roof technology, the ability for the roof to store heat and radiate that heat into the building after sundown is dramatically reduced.

Heitmann Residence featuring a Cool Metal Roof

Cool metal roofs are proven to deliver environmental and performance benefits, of which the most significant to building owners is their contribution to the bottom line. Although savings will vary based upon geography, materials and insulation, the U.S. Environmental Protection Agency estimates that reflective roofs can save up to 40 percent of a building’s cooling energy costs.

When utilizing the U.S. Department of Energy’s Cool Roof Peak Calculator, contractors will discover that the total value of energy savings offered by a cool roof averages more than $1,000 annually in most climate zones for a typical commercial building. Furthermore, this applies to both cool roofing installed over both existing roof insulation and new insulation.

Proven Strategy

As established by documented study and significant heat build-up reduction levels, cool roofs are a proven strategy for supporting longer lasting roofs, reducing both utility costs and decreasing a building’s environmental footprint as Steuben and Richter conclude, “cool roofs are one of the most effective ways to obtain energy savings and environmental rewards through building envelope design and re-roofing projects.”

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)

Selecting Metal Panels Based on Roof Slope

Posted on November 1, 2016July 29, 2024 by Jason Allen

If you’re reading this article, then you are probably already aware that metal roofing can provide many benefits, including longevity, durability and water shedding—not to mention the aesthetic features of today’s metal roof products. When specifying a metal roof system, choosing the correct panel is a key factor. Roof slope is critical in determining that choice. Let’s take a look at some of the main things to consider when choosing a metal roof panel with regard to roof slope, including building codes, minimum slope requirements and typical applications.

Building Codes

Building codes are perhaps the most important driving force dictating the roof slope to choose. Different types of roofs have distinct specifications for installation. According to the 2012 International Building Code (1507.4.2 Deck slope), minimum slopes for roof panels need to comply with the following:

The minimum slope for lapped, non-soldered seam metal roofs without applied lap sealant shall be three units vertical in 12 units horizontal (25-percent slope).
The minimum slope for lapped, non-soldered seam metal roofs with applied lap sealant shall be one-half unit vertical in 12 units horizontal (4-percent slope). Lap sealants shall be applied in accordance with the approved manufacturer’s installation instructions.
The minimum slope for standing seam of roof systems shall be one-quarter unit vertical in 12 units horizontal (2-percent slope).

Minimum Roof Slope Requirements

Depending on the roof profile, there are minimum roof slope requirements for each panel, which need to be considered. The profile refers to the shape the metal sheets take when they bend to form panels. Metal roof slope is expressed by a ratio indicating the roof pitch, which notes the vertical rise of the roof (in inches) for every 12 inches the roof runs horizontally—in other words, dividing the vertical rise and its horizontal span. The most common slopes are: 3:12, 1/2:12 and 1/4:12. When looking at metal roofing panel, you will need to consult with the manufacturer to ensure that the metal panel you selected will work for your application.

Applications: Low Slope or Steep Slope

Commercial Application– Low Slope Roofs

A low-slope roof is one whose slope is less than 3:12. Low slope roofs have several benefits. They have simpler geometry that is often much less expensive to construct and low slope metal roofs require fewer materials than a steep slope, which reduce material costs. Metal roofing panels are excellent solutions for roofs with low slopes. Commercial roofs are typically low slope (less than a 3:12 slope), and larger than residential roofs. This is due to low slope metal roofs being a bit easier to build on large structures.

Cecilia Junior High in Cecilia, Louisiana uses 7,180 sq. ft. of MBCI’s SuperLok®. This panel requires a minimum slope of 1/2:12.

Residential Application– Steep Slope Roofs

A steep slope roof is one whose slope is greater than 3:12. Steeper slopes are ideal for areas that have higher snow loads and will also prevent the possibility of ponding water on the roof. When it comes to residential construction, your roof is a visible part of the structure. Choosing a metal roof for residential construction involves choosing a panel profile that will be aesthetically pleasing.

It is common to use steep slopes in residential applications, such as this home in Guntersville, Alabama that utilizes MBCI’s LokSeam® (requiring a minimum slope of 3:12).

Conclusion

Regardless of whether you’re choosing metal panels for a commercial or residential structure, slope matters. Following common standards, doing your research and paying attention to manufacturer guidelines regarding minimum slope will ensure you’re reaping the full benefit of your metal panel selection.

For More Information

To learn more about metal roof slopes, check out:

The Benefits of Integrating Daylighting Systems with Metal Panels

Posted on July 25, 2016July 29, 2024 by MBCI

When metal roofing and wall systems of insulated metal panels, or IMPs, are combined with integrated daylighting and electrical lighting systems (such as with skylights, windows and translucent panels) it can improve occupant wellness and overall building performance. Are you curious if the return would be worth your investment? Uncover the recent advancements in daylighting technologies, the benefits and how to measure your building’s success.

Advancements in Daylighting Technologies and IMPs

In recent years, IMP assemblies have seen significant improvements, including more effective seals and thermal breaks as well as better thermal performance.

A range of novel daylighting products and technologies have been introduced in recent years that aid in the deployment of natural illumination for a multitude of occupancies—maximizing daylighting effectiveness while also maintaining the envelope’s barrier and thermal performance. These tools include pre-engineered, integrated metal envelope and roof solutions with compatible curbless skylights, light tubes, pan-type prismatic skylights, automated dimming controls for lighting, motorized shades and other components.

One example of how new tools are replacing more traditional products is the use of domed and pan-type units with prismatic embossing, which refracts and directs two to four times as much illumination into the indoor spaces when solar incidence angles are more acute, such as in the early morning and late in the day. These prismatic elements also help eliminate “hot spots” and reduce glare and ultraviolet (UV) deterioration from daylighting.

Benefits of Investing in Daylighting

Overall, using the current crop of novel skylight products in combination with a highly thermally efficient base system of metal panel walls and roofing will reduce excessive solar heat gain as they reduce the electrical base load for lighting. Highly diffusing acrylic and polycarbonate lenses and spectrally selective glass openings are very effective for maximizing functional visible light indoors while inhibiting unwanted heat gain. Many of the skylight aperture designs block 85% of infrared (IR) and 99.9% of UV light, which also reduces the unwanted degradation of products and materials inside the buildings. Additionally, the new generation of skylights also optimizes solar harvesting because many of the lenses have a minimal effect on VT.

In this way, the use of skylights with metal roofing and IMPs can be an effective way to meet the requirements of IECC 2012 and state energy codes. The skylights reduce overall electrical loads without adding unacceptable levels of solar heat gain, and their small relative area means the overall roof U-values remain low.

How to Measure the Success of Daylighting

Building teams will encounter a number of key variables that help measure the effectiveness of proposed daylighting designs. The most common (and valuable) daylighting performance metrics in use today include the following:

• Daylight factor
• Window-to-wall ratio, or WWR
• Effective aperture, or ea.
• Daylighting depth
• Solar heat-gain coefficient, or ShgC
• Haze factor
• U-factor

Using the above tools and terminology, building teams can better assess the benefits of daylighting strategies with skylights, prismatic pan-type products and solar light pipes, among others. In particular, these are important for meeting the widely used 2012 International Energy Conservation Codes (IECC) and ASHRAE 90.1 as well as state energy codes and “reach targets” such as green building certifications, the Passive House standard and others.

How to Learn More

The use of building systems combining metal roofing with skylights and integrated lighting provide significant life-cycle performance. Much of this is due to the research and development behind the individual products and materials used for these applications.

For a more in-depth look at daylighting within the context of metal roof and wall systems, please refer to MBCI’s whitepaper, Shining Light on Daylighting with Metal Roofs, which showcases the strong rates of return of using integrated daylighting systems with novel prismatic optics and high-efficiency lighting on metal envelopes with good thermal and barrier performance.

3 Energy-Saving Technologies to Consider with Metal Roofs

Posted on December 16, 2015 by Amy Crenan

A roof’s primary function is to keep a building weatherproof. A roof’s secondary function—and approaching nearly equal importance—is to be an energy-efficient element of the building envelope. From an energy efficiency standpoint, we’re accustomed to the inclusion of insulation. Are we as accustomed to the ideas that roof color and air leakage matter for energy efficiency? The building industry is embracing all of these technologies in an effort to save energy. So how does an installer make it all work?

Insulation

Photo Courtesy of NAIMA

Insulation requirements for roofs on metal buildings (according to the 2015 IECC) range from R-19+R-11 LS up to R-30+R-11 LS, depending on climate zone. The first layer is draped over the purlins and requires a thermal spacer block with an R-3.5. A second layer is installed at perpendicular and is required to include a liner system (LS), which is a continuous vapor barrier installed below the purlins and is uninterrupted by framing members. The crisscrossed layers help reduce convective air movement within the insulation layer, making the insulation layer more effective. And, good news!—the vapor barrier can also be an air barrier. So, on to air barriers.

Air Barriers

Even small air leaks in buildings can account for a 30 to 40% heat loss during heating season (winter), regardless of the amount of insulation. It can’t be overstated—air barriers are critical to an energy-efficient roof and overall building envelope. The LS, or vapor barrier, can be an air barrier only if the seams of the LS are sealed to prevent air passage. The junction between the air barrier in the roof and walls is critical; it must be joined to be continuous. Often, a separate material (adhered membranes or spray-applied foams) is used as the transition from wall to roof. Or, the roof and wall air barriers might end on opposite sides of a perimeter beam or purlin, connecting the two air barriers. Also, any penetrations through the roof need to be sealed to the air barrier. Being continuous/having continuity is key to constructing a properly functioning air barrier!

Roof Color

We’ve heard a lot about roof color. Where air conditioning is prevalent (e.g., the Southwest), highly reflective roofs make sense, especially if there is minimal insulation. Where heating is prevalent, roof color becomes less effective for energy efficiency for a couple reasons. One, buildings require significant amounts of insulation, and two, there is much less direct heat gain from the sun over the course of a year. Where heating and cooling are both used regularly (e.g., Nashville, Chicago), it’s not a matter of “black or white.” There are many metal roof colors that are moderately reflective, so they balance reflectivity and heat gain as the seasons change.

Contemplate the interaction of insulation, roof color and air barriers on each metal roofing project.

A Common Misconception About Determining Thermal Resistance

Posted on November 24, 2015 by Brad Johnson

Photo courtesy of the U.S. Department of Energy

As an architect, you’re required to design a building’s wall to meet the code-required R-value (or U-factor) in the International Energy Conservation Code. So you design the wall and add up the manufacturer-stated R-values of the components. Done, right? That method only makes sense if walls have no joints, seams, windows, or doors! Let’s think about this.

Accounting for Thermal Discontinuities

The manufacturer-stated R-value of an insulated metal panel (IMP) should really be the R-value in the center portion of the panel, if the manufacturer uses terminology consistent with ASHRAE 90.1. However, a wall is made up of many IMPs, and there are joints between the IMPs. We’ve all seen the infrared photos showing the heat loss at joints between panelized anything—plywood, insulation boards…and IMPs. The joints between each and every IMP are thermal discontinuities, commonly called thermal bridges. These are locations where the R-value is not what you read in the manufacturer’s literature. There are also metal clips and attachments that reduce the R-value of the IMP wall system. If you’re designing a wall system, don’t specify the R-value of the panel and assume it is the R-value of the wall system!

Calculating the R-Value of a Complete IMP System

A building owner deserves a wall that meets or exceeds the code-required minimum R-value or U-factor. The mechanical engineer needs to properly size the building’s mechanical systems based on the ‘real’ characteristics of the building envelope.

Let’s put some numbers behind this idea. Let’s consider a 42 inch-wide panel, 2 inches thick, with a stated R-value of 12. The outer surface of the panel is close to the exterior temperature—say 30 degrees. The metal wraps through the joint, decreasing the temperature of a portion of the metal on the backside of the panel everywhere there is a joint. Clearly this reduces the overall R-value of the IMP as a system. Let’s estimate that the thermal bridging effect of the joints reduces the R-value 5 inches along the edges of the panels to an R-6. That means 30 inches of the panel has an R-12, and 10 inches of the panel has an R-6. That calculates to an average R-value of 10.5 for the panel overall, which is more than a 12% loss of R-value. This is why blindly using the famous equation of R=1/U is dangerous. That equation is only true if the R-value and U-factor involved are consistent with how thermal bridging is or isn’t represented.

U-Factor Testing for Higher Accuracy

It’s clear that the panel joints are thermal bridges, but the extent of loss is really an educated guess. But there is a solution! The forward-thinking IMP manufacturers are performing U-factor testing and finite element modeling, and that includes joints between panels. The U-factor testing is a more accurate determination of thermal resistance.

As an architect designing the wall system, if you use stated R-values, recognize that you’ll need to account for the loss of R-value because of the joints. Or, simply specify panels whose manufacturers are determining the U-factor for their IMPs!

Codes: More than the IBC and IRC

Posted on October 13, 2015 by Brad Johnson

We all know to look to IBC Chapter 15 and IRC Chapter 9 for information about roof systems. These two “Roof Assemblies and Rooftop Structures” chapters include the requirements for fire, wind, impact, materials, and reroofing. But did you know the scope of the building code (IBC Section 101.4) references additional model codes that are considered to be part of the requirements of the IBC? From a roofing perspective, this scoping reference brings into play the International Energy Conservation Code (IECC) and the International Existing Building Code (IEBC).

The creators of the model codes are attempting to ensure that buildings (and roofs, in our case) are designed and built according to the most recent model codes even if they haven’t been specifically adopted by a state or local jurisdiction. If a jurisdiction adopts and enforces the 2015 IBC, by reference the 2015 IECC and 2015 IEBC are in effect.

How do 2015 IECC and 2015 IEBC affect roofs?
The IECC Commercial Provisions include energy efficiency requirements for the same buildings for which IBC Chapter 15 roofing requirements are required. The IECC includes minimum insulation, air barrier, and reflectivity requirements for building envelopes. Prescriptive R-values and U-values are provided for roofs, and they are based on climate zone, metal buildings, and attics. Minimum levels of solar reflectance and thermal emittance are required for low-slope roofs on buildings with air-conditioning in climate zones 1, 2 and 3.

Air barriers—used to reduce or eliminate air leakage—are required for new construction. These are based on materials, systems, or the whole building. Sheet steel and aluminum are listed as materials that meet the air barrier requirements. Of course, the joints and seams are critical to the effectiveness of metal roofing panels when considered to be air barriers. When reroofing, air barrier requirements are not triggered, which is significant. But the insulation requirements are triggered.

Roofing and structural considerations
The 2015 IEBC includes sections about reroofing (Section 706, which is new in the 2015 IEBC) and structural considerations (Section 707). The IEBC divides “Alterations” of buildings into three types: Levels I, II and III. A level I alteration includes the removal and replacement of existing materials. Reroofing is a level I alteration, which triggers the requirements of Chapter 7. The Structural section includes a requirement to upgrade a wind-resisting roof diaphragm when more than 50 percent of the roof is removed where the design wind speed is greater than 115 mph, and in special wind zones. While these are small portions of the United States, it’s important to understand this requirement.

Build roofs with the full scope in mind
Look beyond the roofing chapters to ensure that you design and build buildings according to the most recent building codes.

Code Requirements for Cool Roofs with Climate Zone Specifics

Posted on June 8, 2015 by Brad Johnson

There is still a lot of discussion—some agreeable and some not so agreeable—about the necessary color of our rooftops. One side of the discussion revolves around keeping the surfaces of our built environment “cool,” so there’s a movement to make all rooftops “cool” by making them white, or at least light-colored. Those on the other side of the discussion claim that cool roofs are necessary to reduce a building’s energy use. Cool roofs can be a really good idea, but let’s not mix up the reasons why cool roofs matter—are we cooling the urban areas (that is, reducing urban heat islands), or are we saving energy costs for individual buildings?
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The average building height in the United States is less than two stories, but “white roofs” are mostly desired in dense, urban areas…and how many buildings here are less than two stories? Tall buildings are typically found in dense, urban areas, with shorter buildings dominating the fringe urban areas. In the suburbs and rural areas, one- and two-story buildings are more the norm. So we have a mix of building heights in the United States, but the conflict is that the “cool roof” focus is often where the tallest buildings exist.

And unfortunately, a cool roof on a 20-story building isn’t going to reduce its energy use, especially if the code-required amount of insulation exists on that roof. Rather, reducing energy use of a 20-story building hinges on the energy efficiency of the 20-story-tall walls—R-value of walls, percentage of windows, and solar blocking eaves, just to name a few items. Conversely, the energy efficiency of a one-story big-box store comes down to its roof. And for these buildings, roof color definitely can make a difference. However, our building codes don’t differentiate based on building proportions, but only on geographic location—and that’s problematic. But as designers, we can improve on the code requirements.

The 2015 International Energy Conservation Code provides specific information about cool roofs, which are required to be installed in Climate Zones 1, 2, and 3 on low-slope roofs (<2:12) directly above cooled conditioned spaces. There are two ways to prescriptively comply with this requirement: use roofs that have a 3-year-aged solar reflectance of 0.55 and a 3-year-aged emittance of 0.75. Notice that initial (i.e., new) reflectance and emittance are not specified; long-term values are more important. The second method to comply is to have a 3-year aged solar reflectance index (SRI) of 64. SRI is a calculated value based on reflectivity and emittance. It’s important to understand why a cool roof is desired and to make appropriate design decisions.

To locate metal roof products that meet the IECC requirements, go to http://coolroofs.org/products/results and use the search function to narrow your results or view our finishes’ SRI ratings on our Cool Metal Roofing page.

Air Barriers and Vapor Retarders

Posted on May 13, 2015 by Brad Johnson

Building design and code requirements are readily becoming rooted in building science, which is the study of heat, air, and moisture movement across the building envelope.

Reducing the heat energy transfer (which is bi-directional based on geography and climate) is why insulation is used. And arguably more important is the need to reduce airflow (aka, air leakage) across and through building envelopes. This airflow often includes a lot of heat and moisture; therefore, buildings’ HVAC systems work hard (and use energy…and cost money) to make up for the heat and moisture gains and losses in order to maintain proper interior temperature and humidity levels. Environmental Building News, in an article titled The Hidden Science of High-Performance Building Assemblies (Nov. 2012) , stated “Air infiltration and exfiltration make up 25%-40% of total heat loss in a building in a cold climate and 10%-15% of total heat gain in a hot climate.” This is why the model codes are now mandating air barriers.

The 2012 International Energy Conservation Code (IECC), Section C402.4, Air leakage (Mandatory) provides the requirements for air barriers in new construction. Prior to 2012, building codes did not include air barrier requirements. The first step taken in the IECC was to mandate air barriers in Climate zones 4, 5, 6, 7, and 8 (locations north of the Mason-Dixon Line, in a broad sense). Climate zones 4 through 8 are heating climates, where the largest potential for heat loss occurs. The IECC provides three ways to comply; air barriers requirements can be met through material, assembly, or whole building testing. A blower door test, used to test a whole building, seems to be the most common way used to show code compliance currently. The IECC included a list of materials that prescriptively meet the code requirements for air barrier materials; sheet steel and aluminum are on that list.

Three years later the 2015 IECC went a step further. Section C402.5, Air leakage—thermal envelope (Mandatory) extended the requirement for air barriers by mandating their use in all climate zones in the United States except zone 2B, which is a hot/dry zone. Climate zone 2-dry includes only southwest Arizona, southwest Texas, and a small part of Southern California. Essentially all new buildings in the United States are required to have air barriers, and sheet steel and aluminum remain prescriptive air barriers. It’s important to know that when reroofing, the air barrier requirements do not apply.

The IECC is available for purchase on ICC’s website: www.iccsafe.org.

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