Tag: energy efficiency

Fire Resistance for Insulated Metal Panels

Posted on by MBCI

When it comes to understanding fire ratings for wall panels on buildings, one of the first things to overcome is incorrect information or misunderstanding that sometimes emerges around this topic. In an effort to achieve some greater clarity, let’s look at some of the basics of fire resistance ratings, particularly for insulated metal panels (IMPs).

Building Code Requirements

The fundamental reason that any wall needs to provide some degree of fire resistance is to allow people enough time to safely evacuate from a space or building in the event of a fire, or to prevent the spread of fire between defined areas or whole structures. Building and fire codes have been developed and adopted, in part, specifically to define the situations, building types, conditions and circumstances where different degrees of fire resistance are required to protect the public health, safety and welfare. Therefore, when looking at a specific building and the fire resistance ratings required, the applicable codes must be consulted and the proper determination made regarding the minimum fire resistance requirements for the different exterior and interior walls of that building.

Ratings-Based on Testing

The established means for knowing whether or not a wall meets a particular fire resistance rating is based on conducting a fire test in an independent laboratory. For IMPs, that means a manufacturer needs to submit full-size product samples to a laboratory such as Underwriter’s Laboratories (UL), which will then prepare and carry out the test according to standard, agreed-upon procedures such as ANSI/UL 263, “Standard for Fire Tests of Building Construction and Materials.” The procedures dictated by a standard such as this are intended to be the same for all similarly tested materials or products to determine the actual fire resistance rating for each. When the products are subjected to the prescribed heat and flame under uniform laboratory conditions, then they can be classified based on how well they performed. Some products, for example, may survive the test long enough to qualify for a 1- or 2-hour rating, while others may only qualify for a 30-minute rating before succumbing to the fire.

Urology Medical Office Building MBCI
The Urology Medical Office Building in Virginia Beach, Virginia utilizes 7.2 Insul-Rib® and CF Architectural – Horizontal insulated metal panels. View the product data sheets for these products for information on their fire resistance ratings.

Selecting Products

In creating or renovating a building, then, it is incumbent on the design and construction team to choose products and materials that have a proven, tested fire rating that meets or exceeds the building code requirements for the particular building at hand. If a manufacturer of IMPs has been identified ahead of time, then it may be possible to ask for evidence of the UL or similar test to prove that the selected product or assembly meets the code requirements. But many times, there is a need to first determine the requirements, and then look for the available products and manufacturers who can provide the needed fire resistance. Fortunately, UL maintains an online directory of all of the products that they have tested and certified. Their online certifications directory allows users to input selected criteria to search for specific result reports. Using this resource for IMPs, the UL Category Code of BXUV and the UL File Number of U050 should be entered to do a search. This will yield a summary list referencing the ANSU/UL263 test with a link to the BXUV.U050 test report for IMPs. There you will see under item 2: “Metal faced panels, nominal 42 in. wide by nominal 4 in. thick (for the 1 Hour Rating) nominal 7 in. thick (for the 2 Hour Rating) or nominal 8 in. thick (for the 3 hour rating) installed vertically or horizontally. Panels supplied factory double tongue and grove joint.” This lets the design and construction know that 1-, 2-, or 3-hour ratings are available depending on the thickness of the IMP and given that the factory joint is provided. Hence, the manufacturer can label their products accordingly.

By specifying and selecting the proper products that have been correctly tested and certified, then building code compliance is not only streamlined, the building will meet the inherent fire and safety requirements for the people who will occupy it.

For fire resistance information on MBCI panels, please review the product data sheets.

Combatting Thermal Bridging with Insulated Metal Panels

Posted on 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.

  1. Thermal bridging must be mitigated. In other words, the designer or installer has to try to eliminate as much of it as possible.
  2. 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.

assembled side joint
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

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

Beauty and Braun: The Benefits of Mixing Insulated Metal Panels with Single-Skin Panels in Commercial Design

Posted on by Joe Moore

Commercial projects aren’t one size fits all. By bringing in metal panel products to suit the individual need, designers and architects can provide custom solutions for a variety of applications. Single-skin metal panels and insulated metal panels (IMPs), if used correctly, can together add both aesthetic and functional value to your projects.

While IMPs can provide superior performance with regard to water control, air control, vapor control and thermal control, you may sometimes find your project requires—from an aesthetic perspective—the greater range of choices available in single-skin profiles. Let’s spend a little time looking at some of the reasons behind the growing trend of specifying a combination of insulated metal and single-skin panels.

Benefits of Insulated Metal Panels

Insulated metal panels are lightweight, composite exterior wall and roof panels that have metal skins and an insulating foam core. Their much-touted benefits include:

  • Superior insulating properties
  • Excellent spanning capabilities
  • Insulation and cladding all in one, which often equates to a shorter installation time and cost savings

Benefits of Single Skin

Single-skin panels, on the other hand, with their expansive array of colors, textures and profiles, may have more sophisticated aesthetics. They can be used on their own or in combination with IMPs. It should be noted, too, that single-skin panels can—in their own right (as long as the necessary insulation is incorporated) —satisfy technical and code requirements, depending on the application.

Beyond aesthetics, when it comes to design options, single-skin products offer a wide range of metal roof systems, including standing seam roof panel, curved, and even through-fastened systems. As for wall systems, those may include concealed fastened panels, interior wall and liner panels, and even canopies and soffits, not to mention exposed fastened systems. Therefore, you have a wide range of not only aesthetics options but VE (Value Engineering) options as well.

Why Mix?

So, in what situations might the designer or architect choose to combine the two panel types? Let’s examine a couple of specific scenarios related to the automotive or self-storage worlds as a means of illustration. In both of these types of applications, it is not uncommon for the designer to recognize the importance of wanting to keep the “look” of the building consistent with branding or to bring in other design elements.

Coalville Wastewater Treatment Facility
The Coalville Wastewater Treatment Facility in Logan, Utah combines the insulated CFR panel with the single-skin Artison L-12 panel.

Single-skin panels can be used as a rain screen system in the front of the building or over the office area, and would provide the greater number of design options. In the rest of the building, designers can take advantage of the strength, durability and insulation benefits of IMPs. Although you could use one or the other for these examples, the advantage of mixing the two would be achieving a certain look afforded by the profiles of single-skin, while still adhering to stringent building codes and reducing installation time—which is the practical part of using IMPs.

Focus on HPCI IMP Systems

One great example of a current trend we’re seeing at MBCI is the use of the HPCI-barrier IMP system, along with single-skin panels. The High Performance Continuous Insulation (HPCI) system is a single system that is a practical and effective replacement for the numerous barrier components found in traditional building envelopes.

HPCI Insulated Metal Panels
The HPCI Insulated Metal Panel is quick and easy to install and provides an economical solution to conventional air, water, thermal and vapor control without sacrificing thermal efficiency.

A big benefit to using the HPCI system is that the barrier wall is already in place. In terms of schedule, the HPCI barrier system is typically installed by contractors who are also installing the single-skin system, eliminating the need for multiple work crews, and thereby minimizing construction debris and reducing the likelihood of improper installation. With a general lead time of four to six weeks for the HPCI and a week or two for the single-skin, the installation goes fairly quickly. Therefore, it appeals as the best of all worlds—a single system meeting air, water, thermal and vapor codes (ex.: IBC 2016, NSTA fire standards) plus the design flexibility of a single-skin rain screen product. (Note: The HPCI panel must be separated from the interior of the building by an approved thermal barrier of 0.5″ (12.7mm) gypsum wallboard to meet IBC requirements.)

Bottom line, HPCI design features and benefits include the following:

• Provides air, water, thermal and vapor barrier in one step
• Allows you to use multiple façade options while maintaining thermal efficiency
• Easy and fast installation, with reduced construction and labor costs

Conclusion

As designers, architects and owners are getting smarter about a “fewer steps, smarter dollars” concept and an increased awareness of applicable codes and standards, not to mention lifecycle costs, the trend towards maximizing the strengths of available systems will continue to grow. Whether the right choice is an IMP system, single-skin or some combination, the possibilities are virtually endless.

A Storehouse of Storage Solutions

Posted on by Jeremy Silverstein

With more than an estimated 54,000 storage units spread across the U.S. in 2015, according to IBISWorld, and 2.63 billion square feet of existing rentable self-storage space in 2014, the self-storage industry is booming. In fact, U.S. storage facility revenue topped off at an estimated $29.8 billion in 2014, rising to $31 billion in 2015 and is expected to reach $32.7 billion in 2016. In this growing market, storage builders and facility owners face increased competition and must build and maintain more efficiently and effectively than ever. Metal panels can be a differentiator for this market, especially through multi-story and climate controlled storage facilities.

MBCI Self Storage
Southlake Self Storage in Weatherford, Tex. is a multi-story storage facility utilizing MBCI’s PBU, PBD and PBR metal panels.

Maximizing Sustainable, Rentable Space

Among the cladding and roofing materials available to build these specialized facilities, insulated metal panels (IMPs) are highly energy efficient, deliver a full weather barrier and can be designed without exterior wall framing. This boosts rentable square footage by eliminating exterior wall framing typically built with studs, batt insulation, and liner panels.

Made from 90 percent closed foam, encapsulated inside of two metal panels and impervious to water, IMPs offer a high R-value, which is a big benefit for all storage types, particularly cold storage facilities. Steel panel facings create a vapor barrier and provide long-term thermal stability, virtually eliminating off-gassing found with rigid board insulation. IMPs give design professionals the opportunity to design functional, attractive, sustainable storage facilities, and facility owners the opportunity to lower construction, operating, energy consumption, and maintenance costs throughout the life span of a building.

As an all-in-one air solution—delivering an air, vapor and water barrier with continuous insulation—building teams can strip down the multiple trades to one single application. This means there are no gaps or voids to sap thermal value, and no degradation by air or moisture. Furthermore, IMPs are the most efficient product available, providing an R-value of 7 to 8 per inch vs. the 4.5 for batt insulation, essentially doubling performance. So not only do building teams come away with a thermally superior product, but the IMP storage facility will meet increasing continuous insulation code requirements, such as those mandated by ASHRAE 90.1.

Of course, increasing rentable square footage is one of the biggest draws about IMPs for building owners as those extra four to six inches on the perimeter go straight to the bottom line.

A Modern Style for Storage

Evolving from the standard-looking, plain boxes, today’s storage facilities are taking on a more architectural look to better blend into the office complexes, residential communities and retail complexes surrounding them.

With a variety of high-performance coatings, colors, reveal joints and corrugated sheets with assorted patterns, IMPs offer a large selection of design options to architects looking to create these more trendy designs.

Metal Panels for Self-Storage Buildings
A-AAAKey Mini Storage in utilizes modern colors with 55,000 sq. ft. of MBCI’s Ultra-Dek® metal roof panels.

“The calculated use of smooth, concealed-fastener panels harkens to contemporary design styles with an eye toward the future,” states Ryan Rogers, managing partner, RHW Capital Management Group, Orange, Calif., in an Aug. 2016 issue of Inside Self-Storage. “This can create the perception of innovation and dynamism, communicating to customers that your facility is on the cutting edge of the industry and, as such, a successful leader.”

In order to capitalize on the design and performance options leveraged by IMP panels, architects are advised to integrate these systems from the project’s onset in order to maximize efficiencies and potentially take advantage of longer stands, greater distances and heavier steel gauges.

Multi-Level Storage Facilities

Moving forward, designers can expect to see an increase in multi-story storage facilities, particularly in urban areas, where building owners are being forced onto smaller lots.

Explaining the trend in a Sept. 2016 issue of Commercial Investment Real Estate magazine, Michael Haugh, CCIM, senior director of revenue management, Storage USA, Memphis, states, “Increased land costs have forced developers to build up, particularly in urban markets where land tracks of four or more acres necessary for single-story developments are nonexistent. In some cases, a multistory project can be built on as little as 1.5 acres.”

Or in regions where there is little space for new construction but a high demand for storage, like New York City, storage companies are renovating upward. For example, Stop & Stor partners with door and storage solution company, DBCI to convert existing buildings into high-end, multi-level storage facilities. Using existing building blueprints and outline unit placement, DBCI created a custom storage solution in a space that is both conveniently located and functional For more information, read “Urban Storage Units” in Metal Architecture’s Jan. 2016 issue.

Filling the Storage Niche

From multiple stories to designer-end architecture, IMPs are actively filling an important niche in the self-storage industry as a durable and aesthetic, all-in-one building enclosure solution.

Calculating Cool Roof Energy Savings

Posted on by Candy McNamee

Whether it’s providing waterproofing, reducing thermal expansion and contraction, or supplying chemical and damage protection, cool metal roofing has much to offer. Of course, the most substantial benefit is the energy savings gleaned from reduced rooftop heat levels driving down air conditioning loads. In fact, the Lawrence Berkeley National Laboratory’s heat island group projects a whopping $1 billion reduction in cooling costs if cool roofs were to be implemented on a nationwide basis.

To assist architects in determining the kinds of energy savings that can be expected from cool metal roofing, the Oak Ridge National Laboratory (ORNL) has parlayed the data it gathered from a three-year evaluation of metal roofing products into a whole building energy savings calculator.

Cool metal roofs are offered in a variety of colors.
In addition to energy efficiency, cool metal roofs are known for extended durability and longevity.

Cool Roof Calculator

This calculator is called, simply enough, the Cool Roof Calculator. The easy-to-use tool is described as a quick way to compare overall energy costs and savings for a variety of roof and building conditions. Unlike some energy modeling calculators, which are limited to steep slope residential roofs with attics, ORNL’s tool models the typical low slope commercial roof with insulation placed directly over the deck and under the roofing membrane.

To calculate approximate energy savings offered by a cool metal roof, architects are instructed to input the building’s location, proposed roof R-value, roof reflectance and emittance, base energy costs, equipment efficiencies, electrical demand charges and duration.

While experts suggest that it may be difficult to accurately predict the base use and peak demand without detailed construction and cost information, tools such as the ORNL’s cool roof calculator can be a useful way to gather helpful performance estimations for a variety of building types and locations.

Attempting to do just that, the calculator outputs a number of values to offer an approximate estimate of potential energy savings, broken down into cooling energy savings—a calculation of air conditioning savings from base use and peak demand reductions—and cooling season demand savings, an estimate of the peak demand charge reduction enabled by enhanced roof reflectivity.

Accessible at http://rsc.ornl.gov, users can also compare the energy performance offered by a cool roof vs. a conventional black roof.

“It’s a nice tool to give people a feel for where a cool roof would actually help them and have the greatest impact in terms of energy use,” relates Robert A. Zabcik, PE, LEED AP BD+C, director, research and development, NCI Group Inc., Houston, in a Metal Construction News article.

Roof Reflectance Baseline

Roof reflectance and emittance, requirements and options, can be found in energy codes such as IECC, ASHRAE 90.1, California Title 24, and other local codes. Requirements may vary based on roof slope and climate zone, and may allow for either aged or initial solar reflectance, thermal emittance and/or SRI.

Fortunately, MBCI continues to stay current with individual testing and also maintains third-party tested and verified product listings through entities such as the Cool Roof Rating Council, and the U.S. EPA’s ENERGY STAR®.

Design and Color Trends in New Metal Construction

Posted on by Shelby Shipman

Design and color trends in metal roofing products are not exactly black and white. In fact, a whole host of options are available when choosing textures and colors for new metal construction projects, depending on specific criteria. Some are practical, some are aesthetic—but all are shaping how designers are specifying metal products, coatings and paints. Let’s walk through a few of the top trends in the industry now.

More color options for coil coatings

Bright Color Options in Coil for Design
Through vertical integration, manufacturers are offering more color options than ever.

It used to be that coil options were limited to standard stock choices and availability was determined by the coil coaters. Now, with evolving industry strategies, such as NCI’s vertical integration, many more manufacturers are properly positioned to enter into the market with multiple color choices across multiple brands without as much deviation. This also allows manufacturers to quickly adapt to requests for custom colors—both internally or externally.

Ratings and regulations are leading to more energy-efficient choices

Moreover, color requests based on aesthetics and paint systems have evolved based on changing code requirements. For additional benefits, specifiers can turn to many rating systems, such as the Cool Roof Rating Council and ENERGY STAR®, as well as earn LEED points by having specific SRI (Solar Reflectance Index) values.

Much has changed over the past 10 to 15 years. For instance, the components industry has evolved from customers merely selecting colors based on preference to a more integrated approach accounting for aesthetics, cost and energy efficiency. Today, owners and architects are more likely to consider a color such as Solar White to save on insurance or receive tax rebates. Environmental considerations and regulations have changed the way customers purchase steel, incorporating such issues as unique regulations for different states and weather conditions, LEED points and reflectivity into the atmosphere.

Insulated metal panels used in higher-end architectural projects

Another design trend in the industry is a move towards insulated panels, mimicking what is typical in the aluminum composite material (ACM) world. High-end car dealerships are known for design with ACM. This includes blocked-off designs that can be elongated, can be different colors or have joints in different places. This application has been ACM’s primary wheelhouse for decades. Now that ACM manufacturers have entered into the insulated metal panel (IMP)  industry, more of the design community is considering a thinner, horizontal IMP. The intention is to replicate the appearance of an ACM panel, while reaping the major cost and insulating benefits of IMPs.

Depth of color and texture: the rise of metallic colors

Architecturally, more metallic paints are being used. Historically, metal panels were white, tan or Galvalume. The current trend has expanded to a wider color palette, including mica fluoropolymer. These metallic coatings give depth to the color, adding sheen and sparkle. In fact, there are actually metal flecks in the paint. Metal oxide-coated mica pigments offer up the metallic look and add to the durability.

Signature® 300 Silver Metallic Color Design
Vasa Fitness in Lehi, Utah features MBCI’s FW-120 panel in Signature® 300 Silver Metallic paint.

What’s behind this trend? Designers are thinking about metal roofs in a whole new way. They are looking to leverage colors and properties of paint to bring out a unique architectural appearance not previously available.

Conclusion

Trends in metal construction are as broad as the choices of color and coatings. Whether a reaction to energy savings criteria or simply a desire of an educated consumer to bring new life to their project, it’s worth taking the time to investigate all your options when specifying your next metal project.

The Benefits of Integrating Daylighting Systems with Metal Panels

Posted on 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.

Daylighting with Metal Roofing

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.

Download the White Paper, Daylighting with Metal Roofs

Thermal Bow vs. Thermal Expansion: A Look at Thermal Efficiency in Insulated Metal Panels

Posted on by kbuchinger

Insulated metal panels  (IMPs), a type of lightweight factory-fabricated metal panel,  are a compelling alternative to more conventional roof panel choices. IMPs have a continuous insulating core that works together with metal skins to create a barrier against air, water vapor, and thermal conditions. One major benefit of IMPs, is their thermal efficiency, averaging R-7.0 to 7.2 per inch as compared to R-5.6 per inch for unfaced urethane board stock. Insulated metal roof panels are commonly available in thicknesses ranging from two- to six-inches which generally correlates to R-14 to 42.

Structure of IMPs

IMPs consist of two single skin metal panels and a foamed-in-place core. The foam insulation is made of non-chlorofluorocarbon (non-CFC) polyurethane foam. As an example, MBCI’s IMPs consist of closed cell structure and nominal density of 2.2 pounds per cubic foot. Its closed cell structure also prevents the foam from absorbing water.

Thermal Bow in IMPs

Thermal Efficiency of IMPs
Thermal expansion of insulated metal panels is accommodated by thermal bowing.

An interesting phenomenon with IMP roof panels is that you don’t have to deal with thermal expansion the way you do with single skin panels. On wide, through-fastened roofs, you can have issues with panels slotting around the fasteners. And with standing seam roofs, you have to ensure that the panel clips can handle the anticipated thermal movement. However, insulated panels experience something called “thermal bow.”

An IMP’s exterior metal skin will still expand as it heats up. But, instead of causing the whole IMP to grow in length,  the exterior skin of the IMP will bow up slightly between purlins/joists because the interior metal skin of the IMP maintains a relatively constant temperature. The insulating foam that adheres to this metal skin flexes to allow for this bow. Because of this, thermal expansion is accommodated by the small incremental growth (and bowing up) of the exterior metal skin between each purlin/joist, which are usually spaced five to seven feet apart.

­­­­­Conclusion

Insulated metal roof panels are fixed roof systems that will experience thermal bow between the purlins as opposed to single skin systems, which are designed to allow for expansion and contraction in the panel. With its thermal efficiency benefits, IMP roofs are beginning to get noticed as an alternative for designers looking for a progressive choice to achieve flexibility and function.

Daylighting 101

Posted on by MBCI

In the age of increased energy efficiency requirements in buildings, designers often find themselves spending time and resources squeezing performance out of systems with relatively little gain in efficiency. More and more, building insulation systems seem to fall into this category. The authors of the building codes recognize this as well and have reacted by turning their focus on other metrics like air infiltration where more substantial gains are to be had. A similar situation exists with lighting efficiency. However, when it comes to daylighting, designers are often pushed out of their comfort zone because lighting concepts and terminology is quite esoteric and difficult to comprehend.

Daylighting
m
The truth is that most people take light for granted and aren’t aware of the complexity of lighting for human activity and comfort. Probably the biggest reason for this complexity is the fact that the human eye is the only way we can judge light and although the eye is an evolutionary masterpiece, it has its own idiosyncrasies and no two eyes work identically. For instance, the typical human eye can discern shades of green at much greater accuracy than other colors and because of this sensitivity, green light is often perceived as brighter than other colors at the same energy level. Therefore, quantifying light level for human comfort and function must take this sensitivity into account, leading to some complexity. Here are some basic principles that you need to understand:

A steradian is a unit of solid angle measure. You can think of a 1 steradian solid angle as a cone cut out of a sphere with the apex of the cone at the center of the sphere and cross-section angle of approximately 66 degrees. A unique property of a 1 steradian solid angle is that the area of the semispherical “cap” captured by the cone is equal to the radius of the sphere squared. This makes it a convenient shape to use in measuring the amount of light projecting from a source at the apex of the cone through its interior and onto the cap because the amount of energy passing through any cross-section along the way is always the same. There are 4π, or approximately 12, steradian in a sphere.

Surface area of the "cap" is equal to radius of the sphere squared.

Light is generated at the molecular level by the outer bands of electrons surrounding a given atom. When these electrons become excited at a high enough level, they emit a burst of energy in the form of electromagnetic radiation of a wavelength interval unique to the emitting atom in order to return to a lower energy state. If the energy level is just right, this wavelength will be in the visible light spectrum and viewed as a specific color. White light is formed when many atoms respond at various energy levels distributed across the entire visible spectrum in a pattern such that the energy transmitted is roughly constant with wavelength. The human eye is not responsive enough to discern the different colors hitting it, so an overall stimulation results in a static or “white” response. (There is a similar concept for sound as well, called “white noise”, when the ear cannot detect the individual vibration frequencies.)

The absolute brightness of light is given by the total energy it transfers through electromagnetic modulation. It is determined by summing up the energies transferred by each incorporated wavelength. As light travels from a point source, this energy spreads, causing the amount of energy arriving at a single point in space to decrease as that point is placed farther away from the light source. Brightness decreases with the square of the distance from which it is viewed. In other words, a light will appear ¼ as bright when viewed from a distance twice as far.

Because the human eye is more sensitive to green light than other colors, the brightness it perceives from different lights can only be effectively compared at the same color or wavelength. For light used for human function and comfort, it has been standardized to quantify the brightness at the 555 nanometer wavelength, which is near the center of green in the visible light spectrum, and then adjust for the effect of other colors consistent with how the human eye perceives them. Color is accounted for by weighting the energies transmitted at other wavelengths using the luminosity function. The resulting quantity is called perceived brightness. The luminosity function is similar to a bell curve and it represents how relative brightness of various colors is perceived by the typical human eye. As you might expect, the luminosity curve peaks at a wavelength near 555 nanometers.

Absolute brightness is measured in watts and should only be used when comparing lights of the same color. This should not be confused with power consumption, which is also measured in watts. Perceived brightness is instead expressed in candela and is the only way light of mixed color (on non-monochromatic) can be compared. A one candela light source with a wavelength of 555 nanometers transmits 1/683 of a watt of energy.

It is also important to be able to quantify total light output of a light source. Real-world light sources are not usually of equal brightness in all directions, so candela is not the best measurement to use. To account for spatial variation, total light output is defined as the sum total of light passing through every point in a cross-section of a one steradian solid angle, considering a light source at the apex, divided by the area of the section. This results in the same quantity regardless of the location of the cross-section. So, if a light were to transmit one candela through each point in the cross-section of a unit steradian, then it would be said to produce one lumen of light. Likewise, a 555 nanometer light source radiating one watt per steradian of energy produces 683 lumens.

Finally, the effect of light projected onto a surface must be defined, commonly called illumination level. If a light projects through a solid angle of one steradian at a uniform perceived brightness of one candela, the illumination level achieved one foot away is called a footcandle. This definition confuses many people because it is contrary to what the name might imply. But because a unit steradian is used as the basis, a footcandle equates to one lumen per square foot and it is generally much easier to think of illumination level in this way. Lux is the metric equivalent to a footcandle and there is about 10.8 lux in a footcandle. Since illumination level differences of one tenth of a footcandle are not detectable by the human eye, this is often simplified to 10 lux per footcandle.

To put this all into context, a dome skylight 24” in diameter, elevated a foot above a 30’ high roof on a 20’ x 20’ grid on an open building in El Paso, Texas, achieves about 25 footcandles at a level 4’ above the floor at noon on March 21st (typical spring equinox). Compare this versus the following recommended illumination levels for various tasks as recommended by The Whole Building Design Guide:

Whole Building Design Guide Illuminatin Levels

Understanding these concepts will help you get more out of MBCI’s latest whitepaper, Shining Light on Daylighting with Metal Roofs, where MBCI explores the subject in detail, wholly within the context of metal roofs and metal wall systems. We hope you find it…err, enlightening.

Download the White Paper, Daylighting with Metal Roofs

3 Energy-Saving Technologies to Consider with Metal Roofs

Posted on 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

NAIMA.org
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.

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