## A Common Misconception About Determining Thermal Resistance

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!

## Wellness and Envelopes: Four Ways Single Skin & Insulated Metal Panels Keep Us Healthy

Is there a connection between building design and human health?

We know the answer must be yes, but figuring out how the connection works is the job of experts like the team behind the WELL Building Standard®, a new certification that takes on the question. Among the solutions that can help make a building better? Metal roofing and siding, according to many healthy building experts.

First, let’s learn about WELL. According to the International WELL Building Institute, the WELL Building Standard “takes a holistic approach to health in the built environment addressing behavior, operations and design.” Their performance-based system measures and monitors such building features as air, water, nourishment, light, fitness, comfort, and mind. Two ratings have been offered: WELL Certified™ spaces and WELL Core and Shell Compliant™ developments. Done properly, these “improve the nutrition, fitness, mood, sleep patterns, and performance of occupants.”

Pilot programs are currently available for retail, multifamily residential, educational, restaurants and commercial kitchens projects. In many of these projects, the use of metal claddings and insulated metal panels (IMPs) is recommended by many health-focused professionals. Why?

#### 1. Occupant comfort

IMPs tend to have excellent R-values and very good thermal efficiency – including long-term thermal resistance, or LTTR, a key measure of how the building will perform over time. For the wellness factor from pure thermal comfort, IMPs are highly effective over conventional construction.

#### 2. Nourishment of people and earth

IMPs are often made with recycled metals and improve the energy performance of the building. With energy cost savings ranging from 5 percent to 30 percent, they cut the carbon footprint of the facility. Plus the interior and exterior skins include up to 35 percent recycled content – and they are 100 percent recyclable – reducing impact on the global carbon load.

#### 3. Daylight for all.

Using metal roofs with skylights or light-transmitting panels in conjunction with integrated dimming lighting is a highly cost-effective strategy, and IMP systems also have integrated window systems that increase available sunlight within building interiors. Light is essential for healthy buildings, and daylight is the best kind of all.

In addition, because rigid insulation per inch offers more R-value than per inch of fiberglass insulation and IMPs have metal liner skins, day-lighting fixtures such as light tubes can be integrated more easily with these roofs.

#### 4. Proper moisture and air control.

Issues such as leaky walls and wet, moldy construction materials are anathema to wellness, and must be controlled for healthy building certifications. Mold has a negative impact on indoor air quality and indoor environmental quality, and one of the main culprits is trapped moisture. This can also corrode the metal studs and furring members, even if they are galvanized, leading to structural issues such as reduced fastener pullout resistance and leaks.

### How Does a Building Become WELL Certified?

IMPs used as either rainscreens or as sealed barrier walls backing up a rainscreen are shown to protect against moisture issues and mold over time. They also serve as a continuous layer of insulation and air barrier. In this way, the single-component system can eliminate the need “for air barriers, gypsum sheathing, fiberglass insulation, vapor barriers, and other elements of a traditional multicomponent wall system,” says one industry executive. In fact, many masonry buildings are being upgraded with IMP retrofits on the exterior, directly over the old concrete, brick or stone.

All of these traits of IMPs certainly contribute to more healthy buildings, but do they add up to WELL Building certification levels, such as Silver, Gold or Platinum?

To get there, building teams must undergo an on-site WELL Commissioning process with rigorous post-occupancy performance testing of all the features. If it meets the “preconditions” — the WELL features necessary for baseline certification — WELL Certification is given. If the team pursues “optimization features,” the higher levels of achievement are granted.

## Codes: More than the IBC and IRC

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.

## Storms and Safety: Metal Building Systems, Standing Strong

Welcome to hurricane season, says NOAA! Erika was a near miss, and Henri went off to sea, but with multiple storms stirring up the Pacific and a major El Niño threatening severe weather this year, building teams are focused on resilient, high-performance envelope and roofing assemblies.

## The Durability of Metal Roofs

Resiliency is the watchword, and the stringent Miami-Dade County code language or similar standards are being adopted in many communities. The Florida Building Commission, as well as FEMA and NIST, have done studies of building performance during severe storms, and metal buildings were shown to perform exceptionally well. According to MBMA reports, insulated metal panels (IMPs) perform well under stresses of high winds and projectiles such as hail and wind-borne debris.

The post-storm studies everywhere from Texas to New Jersey confirmed the durability and resistance to driving rain and severe pressure differentials, too. Standing-seam roof systems and IMP façades remained intact during Katrina even as winds hit 120 mph. According to Metal Roofing Alliance, “metal roofing can have a 140-mph wind rating, meaning it can withstand wind gusts up to 140 miles per hour.” MBCI, which has achieved these ratings, has also pointed to another critical standard: wind uplift testing in accordance with Underwriters Laboratories’ UL 580, Standard for Tests for Uplift Resistance of Roof Assemblies.

### Performance During Storms

Detailing of the roof-wall interface is essential to protecting against uplift. To reduce damage from wind-driven rain, manufacturers like MBCI use test protocols from Miami-Dade or the ICC (TAS No. 100-95). These standards show the security and integrity of the seams in IMP and metal roofing systems. For hail and wind-driven projectiles, the metal systems often are able to absorb impact and remain functional and retain their protective metal layers intact even if they may suffer cosmetic damage, as MetalRoofing.com forums have shown. Last, IMPs and metal roofing systems perform very well during lightning strikes — a fact that is counter intuitive but proven. In fact, use of metal roofs does not increase the chance of a lightning strike, as scientific studies show and the Metal Construction Association reported in BD+C, and as you can read more about in our blog post.

Similar to the three pigs of fable, some buildings will do well through hurricane season, while others nearby will suffer from softer connections, more porous materials and less stringent assembly designs. Many building owners will do well with metal roofing and vertical assemblies: with rugged embossed metal sandwiches over high-R-value, rigid insulation, held firmly in place with interlocking joints or lapping seams.

Best of all, the systems are complete assemblies that install as weather-tight barriers without coordinating various components and trades. They also have higher rated values than, for example, EIFS planks or fiberglass panels, some of which may suffer lost R-value when wet. With these benefits – and following the damage and disruptions caused by Hurricanes Katrina and Sandy in the United States – metal is an attractive roofing choice for weather resistance.

## Rooftop Solar Energy

The “Sustainability begets resilience” blog ended with a nod to rooftop energy production. So, how will you respond when, not if, a building owner asks you about rooftop solar energy? An appropriate and accurate answer is, “The combination of a metal roof and solar energy is a recipe for a long-term, high-performance roof system,” or something like that. The fact is a metal panel roof is an ideal substrate for a solar energy system.

### Installation Methods

Solar energy is the broad term for two sub-categories: photovoltaic (PV) systems (electricity) and solar thermal (hot water) systems. Besides the obvious differences, the rooftop attachment concepts for both systems are quite similar. PV panels and solar thermal panels are commonly rigid with metal frames. Attachment to metal roofing panels can be direct or include rails. Both methods use a customized clip that attaches to the metal roofing panel seam; then, metal-framed PV panels or rails are attached. The need for rails (think “purlins”) depends on the seam spacing and layout of the roof panels relative to the size and layout of the PV or solar thermal panels. Overall roof slope matters, too. Directly attached solar energy systems match the slope of the roof, which is not necessarily the optimum slope for energy production.

### Structural & Performance Requirements

Other considerations include the structural load, fire resistance, wind resistance and the use of code-approved materials and components. A solar energy system adds weight to the roof. Does the structure need updating to carry the gravity load as well as any increased wind uplift loads? Adding panels to the roof will increase the sliding load (i.e., drag load) on the clips holding the roof panels to the substructure. And let’s not forget about the potential for snow retention or increased snowdrifts that will add weight.

Fire and wind resistance should be discussed with the manufacturer or designer of the PV or solar thermal system. Fire and wind design are incredibly important, and there are very specific code requirements to meet.

### Layout Considerations

Rooftop layout of solar systems, especially PV, should not block drainage or impede roof maintenance. Also, clearance at roof perimeters and access to critical roof areas (e.g., drains, rooftop units) is necessary. Last but certainly not least, check with the metal panel roof system manufacturer about warranty issues regarding a rooftop solar energy installation.

While there are many things to consider when installing solar energy systems on roofs, the long service life of metal panels and the ease of installation certainly make metal roofs and solar energy a great combination!

## Sustainability Begets Resiliency…In Practice

Sustainability is the buzzword started by USGBC that is pushing us to design and build environmentally friendly buildings.  And that’s a good thing.  However, from a practical—and roofing—standpoint, what we can most readily do with roofs is design them to be resilient.  Roof system resiliency is the tangible aspect of sustainability that the “regular” population can get their heads around.  Resiliency—the ability to bounce back—is understandable.

Loosely speaking, a resilient building can withstand an extreme weather event and remain habitable and useful.  It follows that a resilient roof system is one that can withstand an extreme weather event and continue to perform and provide shelter.

What makes a metal roof system resilient?  It needs to be tough and durable, wind and impact resistant, highly insulated and appropriately reflective, and perhaps be a location for energy production.

An extreme weather event typically means high winds.  A resilient metal roof system needs to withstand above-code wind events.  Remember, codes are minimum design requirements; there is nothing stopping us from designing metal panel roofs above code requirements!  If a building is located in a 120 mph wind zone, increase the design/increase the attachment as if it were in a 140 mph wind zone.  And, very importantly, increasing the wind resistance of the edge details is critical to the wind resistance of a roof system.

Toughness is important.  Increasing the thickness of a metal panel roof system increases resistance to impacts and very likely increases service life (of the metal panel, at least).  Tough and durable seams are important, too.  A double-lock standing seam is one of the best seam types for metal roofs.  A little bit of extra effort at the seam can go a long way for durability, weatherproofing, and longevity.

Highly insulated and appropriately reflective are also traits of resiliency.  High R-value means less thermal transfer across the roof assembly.  Two layers, staggered or crisscrossed, provide a thermally efficient insulation layer.  Using thermal breaks between the metal panels and the metal substructure adds to the thermal efficiency.  Reflective roofs help reduce heat transfer through the roof assembly.  The effectiveness of a roof’s color and reflectivity to save energy depends on many items, such as location, stories, and building type.

Enhanced wind resistance, improved impact resistance and toughness, high R-value, and reflectivity and color are passive design elements that increase the resiliency of a building’s rooftop.  And let’s not forget that rooftop energy production can provide electricity to critical components of a building, such as a freezer section of a grocery store.  Hurricane Sandy put resiliency on the public radar; resilient buildings are here to stay.

## All Those Sustainability Acronyms Mean Something, Right?

By now I’m sure you’ve heard about PCRs, LCAs, and EPDs.  Simply put, a PCR is a set of product category rules; an LCA is a life cycle analysis; and an EPD is an environmental product disclosure.  But what do they mean and what’s the purpose of it all?  In the broadest sense, these are mechanisms used for the sustainability movement.  The most granular is the EPD, which is a product-based discussion (i.e., disclosure) of the environmental effects caused by a specific product or product type.   Architects and building designers use EPDs to compare products in order to select the most environmentally friendly products to be used in environmentally friendly buildings.

Developing an EPD can only happen after the creation of a set of product category rules (PCR).  A PCR sets the rules for creating LCAs and EPDs.  An example of a PCR is “Product Category Rules for Preparing an Environmental Product Declaration (EPD) for Product Group: Insulated Metal Panels & Metal Composite Panels, and Metal Cladding: Roof and Wall Panels,” which was developed by UL through the efforts of the Metal Construction Association (MCA).

Only after a PCR is developed can a verifiable LCA or EPD be developed.  An LCmA and EPD are similar but different.  An LCA uses industry-average data, and an EPD is specific to a product or product type.  For example, “LCA of Metal Construction Association Production Processes, Metal Roof and Wall Panel Products” provides industry-average information about the environmental aspects of three key products: steel insulated metal panels, aluminum metal composite material panels, and steel roll-formed claddings.  This LCA is based on 24-gauge material.

EPDs are typically more product specific.  (An EPD is typically based on an LCA, so most often LCAs are developed prior to EPDs.)  For example, the EPD titled “Roll Formed Steel Panels For Roof and Walls” provides similar environmental data as an LCA, but includes information about 29-, 26-, 24-, 22-, 20- and 18-gauge materials.  This provides additional product specific information that can be used by designers when an industry average is not adequate.  And importantly, more LEED points are garnered from a product-specific EPD than an LCA because of the specificity.  LEED is certainly a driver of this!

LCAs and EPDs used in the roof industry are often focused on cradle-to-gate analysis, and exclude the use phase and end-of-life phase.  Ideally, an LCA or EPD should include the use and end-of-life phases so architects and designers have a complete cradle-to-grave analysis.  Without the use phase, designers are allowed to freely select the service life of a metal roofing product, for better or worse, without industry guidance.  And, the advantages gained through metal recycling at the end of life are also omitted from MCA’s LCA.

It’s all about standardized disclosure of environmentally based product data.

## Code Requirements for Cool Roofs with Climate Zone Specifics

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

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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