LEARNING OBJECTIVES

After reading this article, you should be able to:

• Describe the new and more restrictive energy codes to be introduced in 2013 and how those codes and standards will affect building enclosure design.
• Explain typical code requirements for continuous insulation (CI) and the benefits of this enclosure detail for building performance and sustainability.
• List the types of materials used for air barriers and the general requirements of air barriers for improving building energy efficiency.
• Discuss other factors improving enclosure weather tightness, including moisture control and light transmission, and how those affect energy use.

With this year’s scheduled code updates, project teams are focused more than ever on constructing new and retrofitted building envelopes for the highest possible performance. Employing a variety of new and improved enclosure designs on the market today, it’s possible (and often relatively straightforward) to meet new energy codes, sustainability standards and even increasingly strict building codes.

Still, getting the envelope right is far from simple. Design-phase compromises, value engineering, material incompatibility and jobsite defects or craftsmanship issues can hobble a building’s performance even when all the right features seem to be in place. And in the operations phase, some buildings have displayed issues with uneven thermal protection, moisture and air infiltration that undermine the intended performance level of their overall enclosures.

Bridging the gap from effective design to proper operational functioning is difficult enough. Yet, today’s ever more restrictive codes make it even more urgent, and in some ways tougher, to pull off. To deal with these magnified challenges, project teams are increasingly turning to manufactured wall systems and pre-engineered, panelized wall products.

These industrialized technologies include metal enclosure systems such as flat-plate and lap-seam panels, composite sandwiches of metal and foam insulation, and metal-faced honeycomb and thermoplastic cores. Other insulated structural composites adhere concrete or wood panels to foam insulation, while some use polycarbonate and other clear materials combined with translucent insulation. A similar array of pre-engineered assemblies—tested as systems but built up onsite according to manufacturer specs—are variously called backup systems or universal barrier walls (UBWs). These can receive various claddings, such as rainscreens and troweled-on coatings, while maintaining a uniform substructure and barrier behind.

This robust market of varied enclosure solutions provides project teams and building owners with plenty of choices. Recently, say experts, many of the systems have been enhanced or retooled to meet the needs of more restrictive building codes and energy laws.

“There are many codes and standards on a state, regional and national level that affect both building construction and design. At this point, what has our focus are the upcoming energy code changes mandated by the Department of Energy (DOE) that will come into effect on October 18, 2013,” says Bob Dazel, AIA, LEED Green Associate, a registered architect in Ohio and marketing manager, strategic accounts for Dryvit. The October deadline will bring state energy codes for commercial buildings in line with the 2010 version of ASHRAE Standard 90.1, with many exceeding the rule.

More than a dozen states have begun using the 2009 version of the International Energy Conservation Code (IECC) or an equally stringent standard, earning them DOE grants. A few have accelerated the process, requiring adherence to the more aggressive 2012 IECC in some jurisdictions.

Code regimes will depend on who is building and where. “The IECC is used by the federal government, but states will adopt or modify the energy codes through a legislative process so that it becomes state or local law,” says Dave Evers, vice president of research and development for Butler Manufacturing and former energy committee chair for the Metal Building Manufacturers Association (MBMA). “While we do see early adopters that have already incorporated the 2012 IECC, including Massachusetts, Washington and Illinois, most are not yet even using the 2009 versions. Some states, like Missouri, do not have statewide codes, so local jurisdictions are in the lead.”

Other standards and codes will add to the challenges, including the National Fenestration Rating Council (NFRC) and the American Architectural Manufacturers Association (AAMA), says Bruce M. Keller, vice president of marketing, Kalwall. The two groups are introducing new minimum performance levels for air leakage, U-factor and solar heat-gain coefficient (SHGC) for vertical glazing assemblies.

Additionally, wall assemblies with foam plastic have to conform as noncombustible and fire-rated construction types, complying with Chapter 26 of the IBC, says Heidi Larsen, product manager, Parex USA Inc. “The building codes required that exterior walls of Types I, II, III and IV construction must be noncombustible construction,” she adds. “NFPA 285 has become the primary test to evaluate and regulate the fire performance of combustible materials used on or in exterior walls that are required to be of noncombustible construction.”

Rules for air barriers, thermal insulation and moisture protection are also seen in more codes and standards demanding stricter performance. “Air leakage causes major energy losses,” says Keith Boyer, director of design and development, CENTRIA. “The 2012 International Building Code has language originally established in the 2010 version of ASHRAE 90.1, part of which requires complete air barriers on the building enclosure. The 2012 revision has been adopted in four states already, including Maryland, so air barriers will be more prevalent in the marketplace.”

These and other new requirements for the building enclosure are also seen in green building standards, says Robert A. Zabcik, PE, LEED AP BD+C, director of research and development, NCI Group Inc. “While ASHRAE 90.1 remains the main authority on energy efficiency and their high-performance standard, ASHRAE 189.1 is finally gaining traction; today the USGBC’s LEED certifications rule the green building landscape,” he explains. “But there are other new standards and programs that are gaining popularity.” Among the most important to watch? The International Green Construction Code (IgCC) is poised to take on a significant role because of its integration into the IBC and IECC, says Zabcik, adding that the military branches and the General Services Administration (GSA) will drive the market to some degree when they choose their respective standards.

“Eventually, LEED will become the cutting-edge standard while the others will govern the jurisdictions that want green performance but don’t necessarily need to be the cutting edge,” Zabcik predicts.

Responding to Codes and Standards

In addition to LEED, new design standards are challenging old assumptions in building envelope design. “These include the International Living Building Institute’s Living Building Challenge, the AIA 2030 Challenge and the net-zero building movement; they are encouraging change also,” says Keller. “The codes and standards in force in Western Europe have always been far ahead of the U.S., and have been a driving force for us resulting in our ability to more clearly foresee what is inevitable here.”

But experts like Keller assert that ASHRAE 90.1 will remain the most important standard affecting codes, and that most authorities will refer to the IBC, IECC and IgCC, which incorporate 90.1. The later the version, the higher the expectations for performance. According to the DOE, commercial buildings designed to the 2010 version of ASHRAE 90.1 will deliver energy savings of 18.2 percent as compared to those built to the 2007 iteration.

Dazel and many others on the supply side are working to educate the industry about what these codes say and how they will affect the day-to-day for builders and architects.

“According to the DOE, buildings account for 39 percent of total energy use and 38 percent of total carbon dioxide emissions in America,” says Dazel, a frequent industry educator with more than 15 years experience in the EIFS industry. “Since the DOE is committed to reducing both of these, the new code changes coming this fall will present tighter regulations on new construction, including requiring the adoption of updated energy-related building codes across the country.”

How Manufactured Systems Meet the Need

To meet the demands for energy efficiency and high-performance green building, experts recommend that project teams consider a variety of enclosure approaches to improve the odds of beating the codes and standards. These include techniques for controlling thermal transfer, cutting thermal bridging, reducing solar heat gain and eliminating air and moisture infiltration—all of which undermine the energy performance of building walls, roofs and foundations.

“The reason pre-manufactured components are favored is that they can be tested for total R-value and for air and water resistance,” says Keller. “So the systems are known to meet the codes and certifications required as a system—not just as a material or single component.”

Many of the systems also offer exterior continuous insulation (CI) as well as air- and water-resistive barriers. “These are the most effective ways to meet the new code requirements, by eliminating thermal bridging and air leakage issues often found with traditional stud framing and cavity insulation,” says Dazel.

Other products focus on ways to shield and add structure to the insulation and barrier layers. Insulated metal panels (IMPs) are one example, says Zabcik. “IMPs provide excellent structural capacity, durability, insulation performance and a continuous air barrier in an all-in-one solution,” he explains. “But don’t count out high-performance fiberglass systems either. Liner systems and filled cavity systems minimize the batt compression that has been rejected in recent codes.”

Novel techniques for proven building systems, such as EIFS, offer ways to increase overall R-value of the wall assembly, says Larsen. “The typical insulation used in EIFS is expanded polystyrene, or EPS, which provides an R-value of 3.85 per inch,” she says. “This can be installed up to six inches thick or more, a proven method to deliver superior energy conservation in a lightweight wall assembly.”

Beyond R-value alone, other techniques for improving energy performance include the use of low-emissivity (low-E) glass and coatings, as well as light-colored or reflective surfaces. “It is surprising how much of a difference roof color can make,” says Zabcik. “Fine-tuning the solar reflectance and thermal emittance with the building and site climate can shave a few additional percentage points off with no extra cost, at least for a metal roof.”

Many of these systems are designed for opaque enclosures, which are increasingly specified due to the focus on controlling a wall assembly’s solar heat gain coefficient (SHGC). Yet increased daylight and more views to the outdoors are desired by many green building standards. “Adding improved daylighting possibilities are products such as translucent structural sandwich panels, which are highly insulating and light-transmitting fenestration systems,” says Keller. (See sidebar, “School Balances Energy Efficiency and Daylighting,” page 61.)

As for the air- and moisture- barrier construction, methods such as insulated metal panels—and UBWs, also known as insulated composite backup panels, or ICBPs—offer project teams a way to ensure that the required enclosure barriers are provided using a single product or system type. These help address transitions from one cladding material to another—often a weak point for the enclosure—and at interface zones, such as at window openings and through-wall penetrations. “For this reason, we’ve focused on the need for an insulated composite product that can establish the four needed barriers as a backup panel,” says Boyer, describing the ICBPs. “The cladding is an exposed exterior element that can vary, but you have a consistent backup using these insulated composite backup systems.”

New Focus on CI and U-Factor

One of the benefits of panelized and pre-engineered enclosures is the ability to specify a continuous layer of insulation that is not interrupted by metal studs, girts or steel columns that can act as thermal bridges carrying heat and cold unintentionally across the envelope assembly. “With a system like EIFS, the insulation is installed on the exterior of the building, so thermal bridging is eliminated—resulting in a 20 to 30 percent reduction in annual energy costs,” says Dazel.

In fact, about 90 percent of U.S. jurisdictions now mandate CI for all enclosures above grade that are framed with heavy or light-gauge steel, except the areas across the southern states located in DOE climate zones 1 and 2.

“Energy codes have changed so much that the code-mandated R-values are much higher now for opaque walls, although window R-values haven’t changed as much,” says Boyer. “About 10 years ago in climate zone 4, ASHRAE 90.1 required R-8.1; today the minimum is R-15.6—almost double—for solid wall areas.” An even more restrictive insulating value of at least R-10 is required across the entire envelope in the 2012 IgCC and ASHRAE standard 189.1, the highest now mandated. Cavity insulation must supplement the CI layer to achieve at least R-13 in climate zones 3 and up.

By definition, CI must run across the enclosures without interruption, such as mineral wool, spray foam or rigid foam insulation. It can be installed within the enclosure assembly, on the exterior or interior, depending on which approach is best for controlling associated concerns, such as condensation and heating/cooling efficiency.

However, Zabcik says, “There is quite a bit of misinformation about continuous insulation requirements in the marketplace.” For example, the purpose of requiring CI is to make the total in-place thermal performance of an assembly closer to that of insulation alone with no breaks by limiting thermal bridges. While R-value tables in the codes provide simplified descriptions of assemblies needed to get to a certain performance level, they are often misunderstood to be an absolute code requirement, which is not the case, Zabcik explains. “Most codes offer a U-factor compliance path as well, and at the end of the day, the lowest total assembly U-factor is the winner, regardless of whether it uses continuous insulation or not.”

In other words, says the DOE, if the full specified assembly provides a U-factor that is “less than or equal to the appropriate climate-zone construction requirements,” it doesn’t matter what kinds of insulation or R-values are used, Zabcik notes. The IECC Table C402.2 provides details on both prescriptive and performance-based compliance. A whole-building energy analysis is another alternative method for determining if the enclosure design is adequate. 

The ROI of CI

Examples of the benefits of CI are not hard to come by. In designing the Metro Career Academy in Oklahoma City, for example, architect Fred Quinn substituted a brick-face EIFS system instead of brick masonry or veneer. This decision not only cut costs and at least 15 weeks from the construction plan, but it also ensured that an uninterrupted blanket of CI would earn energy savings of at least 34 percent and cut energy costs by almost 43 percent annually. For a single 12-month period, electric usage was a full one-third lower than a baseline established by another of the academy’s campus buildings, saving about $17,500; natural gas use was lower by almost three quarters, for a savings of about $4,800.

By using continuous exterior insulation instead of clay brick, the Metro Career Academy became the first LEED Gold-certified building for career technologies in Oklahoma, says Dazel. “The efficient, sustainable design of this high-performance building was important for it to fulfill its purpose,” he adds.

Another option for CI similar to EIFS is insulated stucco, says Larsen. “Stucco has been used for generations and provides a highly desired aesthetic and a strong outer shell to act as the cladding and thermal continuity for a structure,” she explains. “Like EIFS, stucco-clad wall assemblies can be designed with continuous insulation of EPS or other insulation types, up to two inches thick, thus offering an advanced, energy-efficient assembly.”

When using the EPS or other foam insulation, the façade assemblies must also meet the requirements of the National Fire Protection Association (NFPA) standard NFPA 285. Required in the IBC, the test is used to show that the combustible foam plastic insulation does not propagate flame across the exterior or into the wall assembly. It involves a relatively elaborate setup: a full-scale, two-story mockup of the proposed envelope construction is subjected to a fire plume that is emanating from a room below. Wall assemblies that pass NFPA 285 show limited vertical and horizontal spread of the fire, as measured by temperatures in the wall area and visual damage, measured in feet.

The main challenge of the test? It does not apply to individual materials, according to Jesse J. Beitel, a senior scientist, Hughes Associates. “NFPA 285 is a test of a complete wall assembly and applies only to the tested construction—similar to ASTM E119,” says Beitel. Substitutions of one material for another may cause different test results, including combustible materials such as insulation and weather-resistive barriers (WRBs). This fact tends to lead many project teams to use manufactured panels and other pre-engineered assemblies because they have typically been tested and approved to meet NFPA 285.

Air Barriers, Getting Better

As noted by Beitel, the codes require that if any combustible WRBs are included in a wall design more than 40 feet tall, they must meet the standard test for flame propagation. Because WRBs—including air barriers, vapor barriers and waterproofing layers—are now called for by many codes, project teams have even more incentive to consider using enclosure assemblies that have already passed the fire tests.

“The energy codes and standards have numerous, specific requirements for air barriers,” says Larsen. “By using air barriers, climate-controlled interior air stays inside and uncontrolled air stays out of the building, reducing the building’s HVAC system energy consumption to maintain the desired air temperature and humidity.” Air barrier materials include the company’s liquid-applied combined air barrier and WRB, as well as an array of self-adhering sheets, medium-density sprayed polyurethane foam (SPF), and mechanically fastened commercial building wraps and board stocks, according to the Air Barrier Association of America (ABAA).

The key test for any air barrier material is ASTM E2178 – Standard Test Method for Air Permeance of Building Materials. Different from “air leakage” through openings in an air barrier, permeance describes the capacity of the product used to allow air to migrate through the body of the material, says ABAA. Barriers are considered to be impermeable even though they may allow some air through; one definition widely used in the codes is the standard ASTM E-2357, which states that an air barrier material must have an air permeance of less than 0.02 liters per second per square meter at a pressure differential of 75 Pascal, usually abbreviated 0.2 L/(s·m2) @ 75 Pa. Water-vapor permeance is another measure for air barriers that are also used to resist vapor intrusion. Other tests are recommended for the barrier materials, including the following required for all products listed by the ABAA:

• Self-adhered sheet air barriers are tested for air permeance, water vapor permeance, resistance to puncture, tensile strength, water resistance, peel or stripping strength of adhesive bonds, lap adhesion, low temperature flexibility, nail sealability, pull adhesion, tear initiation and propagation, and crack bridging.
• Liquid-applied membranes are tested for air permeance, water-vapor permeance, nail sealability, pull adhesion and crack bridging.
• Medium-density SPF is tested for air permeance, water-vapor permeance, flame-spread characteristics, thermal transmission, compressive strength, density, tensile strength, dimensional stability, water absorption, open cell content, pull adhesion and crack bridging.
• Mechanically fastened commercial building wraps are tested for air permeance, water-vapor permeance, dry tensile strength or dry breaking force, pliability and water resistance.
• Boardstock, or rigid cellular thermal insulation board, is tested for air permeance, water-vapor permeance, compressive strength, thermal resistance, flexural strength, water absorption, dimensional stability and tensile strength.

Once the right material is selected, the next challenge is for the project team to ensure the entire air-barrier assembly conforms to the codes and meets the requisite level of performance. In this way, panelized and manufactured systems help to ensure the air barrier is structurally supported and continuous across the entire façade area. “When it comes to barriers for air and water, the most important thing is that the products are not just tested as a material or single component, but that the assemblies meet all test criteria,” says Keller. “For panels that are already fabricated, you don’t have to worry about onsite coordination of the exterior cladding, so there is less chance for errors and there are fewer joints to seal.”

A number of federal agencies require air barriers for their building projects, and some jurisdictions and several states have already made air barriers a firm mandate, including Massachusetts. “As more codes—such as the DOE’s October 18, 2013, mandate—come into effect across the country, governing and regulatory bodies are constantly requiring builders and designers to use techniques that better control air and water barriers,” says Dazel, encouraging architects, builders and building owners to seek out solutions for ensuring both their new construction and renovation projects meet requirements.

The stakes are high for individual building performance as well as across the national stock of facilities. According to DOE, as much as 40 percent of the energy used for mechanical systems is required to counteract losses from uncontrolled air leakage. The agency says its goal to reduce building energy consumption by 50 percent before 2020 will require the use of more air barriers.

Many of the panelized, prefabricated enclosure systems have included continuous, structural air barriers for decades. “Metal panel systems have always been good air barriers,” says Zabcik. “Our industry has used assembly air-barrier tests long before they were a code requirement. We learned many years ago that it just takes good, careful installation.”

Moisture Control: Drain and Dry

“Air barriers can also provide a water-resistive barrier, which provides a structure with a durable, seamless moisture barrier resulting in superior drainage protection,” says Larsen. As an ally in protecting the building from degradation and reduced insulation effectiveness, among other challenges, the WRB is essential. But experts say so is a means for drainage and drying of the enclosure, so that moisture from rain, condensation or water vapor is drained out and away from the building, and moved down and outward by means of layered materials such as barrier materials, flashing and waterproofing.

Another concern is preventing the movement of water vapor from areas where it can cause moisture accumulation. “It really is a matter of designing and installing the product assemblies properly so that they are not exposed to water vapor where the temperature crosses the dew point,” says Zabcik. “There are excellent software tools available now that allow the designer to model the assembly using climatic data and ensuring the vapor barrier is in the proper place.”

Other means for water to enter the building enclosure include effects that occur with porous materials, such as inward vapor drive, which impels moisture into the enclosure, as well as capillary action, which can pull exterior moisture upward and inward. In these cases, an air space in the enclosure backed by a WRB across a continuous drainage plane will help prevent propagation of the moisture beyond porous claddings including wood, manufactured stone, concrete panels and the like. Manufacturers caution that traditional underlayments, such as commercial roll “wrap” materials and asphaltic papers, may not be sufficient to stem moisture migration; in addition, any WRB material will benefit from use of a ventilated gap of at least 3/8 inch, which can be maintained with a variety of materials or details. Modeling and testing by some manufacturers ensures that diffusion and drying in the ventilated gap will be sufficient to allow moisture to exit the envelope assembly too. 

According to CENTRIA, windward-facing walls are subject to more driving rain than leeward, protected walls. Wind parts as it flows around the building, so the center of the wall tends to be less vulnerable. At the sides and top edges of the wall, the wind accelerates, driving more rain into these façade areas; the taller and narrower the building, the more discrepancy in wetting intensity. An effectively designed enclosure will also be able to resist water penetration caused by air-pressure differential outside and inside the building. The movement of water behind the cladding caused by pressure differences—for example, during wind-driven rain—is tested for many prefabricated exterior systems using such standards as ASTM E 331, which is used for exterior windows, curtain walls, skylights and door assemblies. Insulated metal panel systems, EIFS claddings and insulated translucent façade systems also have been tested to E 331.

Boyer advises the use of nonporous cladding materials to help reduce overall moisture penetration and associated enclosure problems it can cause. Engineered metal systems, for example, offer advanced joinery technologies that control the entrance and formation of moisture and water vapor, he adds.

In summary, an effective, water-managed enclosure system requires four components, says Dr. Joseph Lstiburek, P.Eng., principal, Building Science Corp., who investigates building failures. “Flashings and other layered materials, weep holes or other means for water to exit the envelope, a continuous WRB drainage plane, and an air space between somewhere between the cladding layer and the drainage plane.”

In spite of how important this is to high-performance building envelopes, however, some new energy codes and green building codes do not include provisions for moisture control. The 2009 IECC, for example, does not have language requiring vapor retarders and similar measures. Instead, the IBC and International Residential Code (IRC) have been modified to include the key requirements for moisture protection.

Summary: Controlling Heat, Air and Moisture

In all cases, the most important part of ensuring conformance to new energy codes is to control HAM—heat, air and moisture. Project designs for energy-efficient walls require an understanding of the climate as well as specific computations for condensation, expected air leakage of typical assemblies and materials, and other psychrometric properties. Some façade systems should be studied for the impact of stack effect, in which pressures are generated by warm air rising within the enclosure and the building. Material properties for the enclosure and typical weather data help complete the picture.

Another part of controlling heat is thermal gain from sunlight, which is more pronounced in glazed assemblies. Yet while the new codes will focus on reducing heat gain, many of the sustainability standards will reward increased daylight and views for building occupants.

This will be a fundamental challenge of tomorrow’s building enclosures, say experts. New versions of energy codes and building codes will call for lower window-to-wall ratios: prescriptive requirements in the 2012 version of the IECC, for example, call for 30 percent window-to-wall ratio (WWR) and 3 percent skylight area, which is stricter than the 40 percent and 5 percent, respectively, allowed by the 2010 version of ASHRAE 90.1.

According to experts in the energy codes, the ratios can be used as prescriptive rules, but there are also performance-based criteria based on total wall U-factor, for example. As long as the whole-building energy consumption meets the requirements of IECC or the 90.1 standard—proven through calculations or modeling software—the enclosure design will pass muster. To improve the performance of walls with large portions of glazing, a number of low-E coatings are available to improve SHGC while keeping desired attributes such as visible light transmission (VLT) levels as high as possible. Some solar control products are available that can be built into the façade. Many of these glazing products, shades and light shelves are available with today’s manufactured and prefabricated enclosure systems.

With this year’s updates to energy codes and international building codes, it is more critical than ever to build high-performance exterior systems. Manufactured wall systems and pre-engineered, panelized wall products are more frequently used by project teams to reach their energy-efficiency goals and to achieve sustainability certifications, too. With the many new and improved enclosure designs on the market today, there is likely an ideal solution for every type of building and project need.