Tag Archives: 07 24 00–Exterior Insulation and Finish Systems

Exterior Wall Assemblies: Are you getting what you specified?

All photos courtesy Dryvit Systems Inc.

All photos courtesy Dryvit Systems Inc.

by J.W. Mollohan, CSI, CCPR, CEP, LEED GA

The exterior wall assembly of a building typically results from the integration of numerous individual building—materials from different manufacturers that are installed by multiple trades and subcontractors.

Generally, the specifier selects a basis of design (BOD) for these wall components, drawn from previous experience and trusted advisors’ recommendations. The specifier may also include a list of comparable material options from alternate manufacturers. However, when this process reaches the bidding stage, the design team loses control of which products are selected.

This common practice raises some practical questions. Who is responsible for determining and confirming the installed products are code-compliant as a complete exterior wall assembly? Will this particular wall assembly satisfy the more stringent requirements of the 2012 International Building Code (IBC) and International Energy Conservation Code (IECC)? These codes address multiple and overlapping issues of thermal, moisture, air, and fire performance for both the individual materials as well as specific assemblies of those materials.

When it comes to fire safety, IBC references National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-load-bearing Wall Assemblies Containing Combustible Components.1 This is the standard for fire testing in exterior walls when combustible materials such as foam plastic continuous insulation (ci) and water-resistive barriers (WRBs) are components within the wall assembly.

The stringent and expensive test provides a specific method of determining the flammability characteristics of complete exterior, non-load-bearing wall assemblies/panels. It is intended to evaluate the inclusion of combustible components within wall assembly panels of buildings otherwise required to be of non-combustible construction. As such, the test is designed to emulate the actual fire-resistance performance of the wall assembly in a constructed building.

NFPA 285 compliance is required for Type I–IV commercial buildings of two stories or more where exterior wall assemblies integrate combustible claddings, veneers, and/or foam plastic insulations. For 2012 IBC, WRBs must now also be NFPA 285-compliant for commercial buildings of Type I–IV construction when integrated within wall assemblies above 12 m (40 ft) in height. Whether cited in the specification or not, the test requires the specific assembly of products and materials intended to be installed in the wall is tested to comply.

Typical components of an exterior insulation and finish system (EIFS) system.

Typical components of an exterior insulation and finish system (EIFS) system.

Multiple choice specifications
As already noted, specifiers stipulate what is needed, but commonly accept any combination of competitive materials meeting the same performance criteria. The contract documents convey the design intent to comply with code, or more specifically to comply with NFPA 285. Should this responsibility be transferred to a general contractor or sub-trade? Who is ultimately liable for determining whether the as-installed assembly has been tested and complies? And, at what project stage is this going to take place: pre- or post-bidding?

Everyone wants to minimize the risk of a non-compliant assembly being installed. A code enforcement official requiring a test of the as-bid assembly can create prohibitive additional costs and delays.

This can be extremely complicated, as traditional foam plastic continuous insulation and WRBs may be standalone products with limited, if any, testing as a complete wall assembly. As a result, some manufacturers of these components are attempting to create alliances with various cladding manufacturers to test and offer ‘typical’ code-compliant assemblies.

However, this level of cooperative testing is limited and may not be acceptable to some jurisdictions where attempts are made to simply ‘blend’ individual materials or ‘similar’ assembly test reports together to represent the project specific wall assembly. This may also leave owners and designers questioning whether the general contractor can provide a wall assembly solution composed of individual materials both compatible with one another and code-compliant, from all the possible specified or substituted variations and combinations. That uncertainty is multiplied by separate sub-contractors installing the various components of the exterior wall assembly. It is difficult for the project team to have confidence the constructed exterior walls will satisfy the specifications’ requirement of a code-compliant assembly.

EIFS provide continuous insulation (ci) to meet the latest code requirements, such as National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-load-bearing Wall Assemblies Containing Combustible Components in a wide variety of architectural finish options.

EIFS provide continuous insulation (ci) to meet the latest code requirements, such as National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-load-bearing Wall Assemblies Containing Combustible Components, in a wide variety of architectural finish options.

Specify and install tested assemblies
Rather than exposing the owner to these risks, the project team can identify a sole source responsible for manufacturing, testing, and warranting the complete exterior wall assembly from the sheathing out. Such complete single-source wall assemblies offer the greatest likelihood the installed system will truly meet the design team’s intent, as well as requirements for code compliance, material compatibility, and specified performance. The alternative is to fully test the proposed wall assembly at substantial cost and time in the hopes it will pass.

An exterior insulation and finish system (EIFS) is a prime example of this type of single-source assembly. Structural wall components, such as exterior framing and sheathing, are already in place at the site before application of the EIFS. A single subcontractor then installs the system’s components, often in a single mobilization. All the EIFS components are sourced from a single manufacturer who can offer exhaustive testing, code compliance, and solid warranties on the systems’ quality and performance. The result is a lightweight, high-performance, and code-compliant exterior wall assembly.

Modern exterior insulation and finish moisture-drainage systems meet all current building and energy code requirements through their integration of proprietary WRBs, compatible flashings, continuous insulation, and integrated detailing for the development of continuous air barriers. Additionally, the systems include a finish surface available in various styles, colors, and aesthetic appearances such as stucco, brick, limestone, granite, and metal.

In this project a single-source system with a metallic finish was used.

In this project a single-source system with a metallic finish was used.

EIFS thicknesses, variations, and details are extensively tested and can be installed over a broad range of commonly available structural and non-structural wall substrates in both new construction and renovation.

The benefits of this single-source system include:

  • ease of specification;
  • greater control of the bidding and construction processes;
  • simplified contract administration;
  • improved coordination of entire exterior wall components; and
  • conformance with all aspects of code requirements and architectural design.

Case study: Metro Career Academy
It is not an overstatement to say clay brick masonry is the foundation of modern Oklahoma City. The look of brick and stone masonry continues to be popular with area architects and building owners everywhere. However, the ever-increasing demands of climbing construction costs, energy efficiency, and lifecycle performance led architect Fred Quinn (Quinn & Associates) to research different materials to meet the demands of the high-performance Metro Career Academy (MCA).

The original design of the MCA building called for 2229 m2 (24,000 sf) of clay brick and 1207 m2 (13,000 sf) of cast stone. When Quinn learned he could use an EIFS for the same look and save nearly 50 percent in construction costs versus the clay brick and stone, it was an easy decision.

In addition to this dramatic reduction in cladding costs, making the decision to switch to EIFS during the schematic design phase, allowed the owners of the Metro Career Academy to harvest the full range of benefits from the lightweight cladding, including:

  • less structural support;
  • reduced construction schedule; and
  • projected energy savings and fewer delivery trucks (i.e. reduced environmental impact).

By substituting the 0.07 kPa (1.5 psf) adhesively-attached EIFS with moisture drainage system for the labor-intensive 1.9 kPa (40 psf) masonry and stone, the designer was able to subtract more than 96 percent of the anticipated weight of the building’s skin. Eliminating 646,142 kg (1,424,500 lb) from the exterior walls of the building produced additional savings in the concrete and steel support system required to carry that initially designed load.

Metro Career Academy utilized products to simulate the brick and limestone found throughout the red river area.

Metro Career Academy utilized products to simulate the brick and limestone found throughout the red river area.

Cris Callins, manager of preconstruction with general contractor CMS Willowbrook, estimated the reduced demand for structural support and the rapid installation of the EIFS system allowed the project manager to cut a full 15 weeks from the MCA building’s construction schedule, lowering labor, equipment, and insurance costs while easily meeting the owner’s demanding completion date.

The project used 101.6 mm (4 in.) of exterior continuous insulation (ci) as part of the single-source EIFS system. This helped MCA achieve Leadership in Energy and Environmental Design (LEED) Gold certification. The project earned the full 10 points in the Energy & Atmosphere (EA) Credit 1, Optimize Energy Performance. The computer-modeled performance anticipates an energy usage savings of 34.8 percent and an energy cost reduction of 42.8 percent annually compared to the baseline. Without taking into consideration rising costs of energy or inflation, it is possible to conservatively estimate the value of these energy savings over a 50-year lifecycle of the MCA facility at more than $1.7 million.

Overall, the EIFS assembly allowed the entire project team to increase the insulation value of the wall, enhance the moisture protection of the building envelope, and lower the cost of the exterior cladding, while retaining the desired look of masonry and stone. The single-sourced, fully-tested system meets all of the new code requirements, including NFPA 285.

The Gaylord Palm Hotel in Kissimmee, Florida employed a single-source EIFS.

The Gaylord Palm Hotel in Kissimmee, Florida employed a single-source EIFS.

Conclusion

Everyone involved in the design and construction process has an interest in ensuring installed exterior wall assemblies match the specifications. As demonstrated, this means the assembly must be tested as a complete system. Whatever the authority having jurisdiction (AHJ), the code enforcement official has the right to demand proof of testing compliance in the interest of protecting the public. The licensed design professionals on a project have a similar right to demand compliance with the specifications on behalf of the owner who is paying for a compliant building all in the interest of protecting

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the health and safety of building occupants.

Delivering exterior wall systems through a single-source solution for manufacturing, code compliance, and warranty, is a proven method of assuring these desired outcomes. In addition to creating a high-performance system, this approach saves time and money for all parties. Perhaps most importantly to all of us, it yields an installed exterior wall system that can readily meet the complete quality and performance standards of the specifications.

Notes
1 For more on this standard, see the article, “Specifying NFPA 285 Testing,” by Joseph Berchenko AIA, CSI, CCS. (back to top)

J.W. Mollohan, CSI, has 30 years of experience in the design and construction industry, and is currently a strategic markets manager at Dryvit Systems Inc. He is a member of the Leadership Team of the Kansas City Building Enclosure Council (BEC), and president of the North Central Region of the Construction Specifications Institute (CSI). Mollohan chairs CSI’s national membership committee. He can be reached at jw.mollohan@dryvit.com.

Energy-efficient Building with EIFS: Retrofitting at Silver Creek Resort

Silver Creek in Snowshoe, West Virginia, used an EIFS system which included a fluid-applied waterproofing air barrier to restore the high-rise resort. [CREDIT] Photos courtesy Sto Corp.

Silver Creek in Snowshoe, West Virginia, used an EIFS system which included a fluid-applied waterproofing air barrier to restore the high-rise resort. Photos courtesy Sto Corp.

by Tom Remmele

Far away from any major city, the nine-story, 239-unit, high-rise Silver Creek Resort in Snowshoe, West Virginia, has undergone a complete claddings renovation.

The resort’s exterior was a panelized exterior insulation and finish system (EIFS) that had been experiencing water leaks since its 1985 installation. Incorrect installation and maintenance was the cause of the leaks, according to Sam Collins, general manager.

Once there was a decision to restore the building, the team worked with an architect and considered

metal panels, fiber cement, and other claddings. In the end, however, a 127-mm (5-in.) drainable EIFS was specified because it was deemed to be the best fit and had the best R-value (i.e. approximately R-19 of continuous insulation [ci].)

Specifying EIFS
The system includes a fluid-applied waterproofing air barrier, and finish with a pronounced self-cleaning effect. This project consisted of 11,612 m2 (125,000 sf) of wall cladding.

Snowshoe’s climate includes some of the most extreme wind, snow, and rain in the Southeast. Prior to the renovation, whenever a severe storm came through, management had to deal with damages and continue to ‘Band-Aid’ additional problems.

According to Collins, when the original EIFS was installed there was no option for substrate protection, air barriers, or drainable systems, but this has since changed and staying informed is key.

Before starting the project, building sections had to be opened up to identify the existing condition behind the wall. Issues such as how the EIFS panels were hung on the building, window leakage, and imperfect seals had to be identified so a solid, watertight building with the new cladding could be created.

“We had to remove all the original exterior skin including the EIFS, exterior sheathing, and wet wall cavity insulation before we could begin,” said Gabriel Castillo, of EIFS-installer Pillar Construction. “The trend now is to insulate outbound of the exterior sheathing taking the insulation out of the cavity, and we did just that.”

The renovation begins
Members of the resort’s board of directors knew something had to be done. The building had been leaking for more than 25 years, and the damage would only escalate. After looking at various cladding options, they decided to employ EIFS.

After the initial drawings, they worked with architect Peter Fillat who came up with the design plans to maintain the building’s strong architectural façade.

Adding a continuous air and moisture barrier—now code in most states—gave the building a R-value not compromised by the thermal bridging effect of stud framing. The air barrier was connected to the windows to give it a tight seal. West Virginia has adopted the 2009 International Energy Conservation Code (IECC), which requires both ci and air sealing.

All 740 windows needed to be replaced. The new assemblies were thermal break horizontal sliding and fixed, and played a big part in energy savings. Without thermal breaks, the window frame becomes a thermal bridge to the exterior and a conduit for energy loss and a possible source of condensation in the wall section.

The previous installation had expansion joints between each panel, but because the renovations removed everything down to the studs, the panel-to-panel joints in the substrate were eliminated. This allowed the air barrier to run continuously between the panels and provided less opportunity for water and moisture to get in.

Challenges
The project was completed in two phases over more than two years. The building was occupied during the entire transition with full-time residents and vacationers. Getting all the ownership together was the first challenge, according to Castillo. However, something needed to be done immediately.

The next challenge was the climate. Silver Creek is located on the ski slopes and sits at 1280 m (4200 ft) above sea level. The average annual snow fall is 4572 mm (180 in.). The decision to renovate was made in early 2011, however, because of the winter, construction had to wait.

The final challenge was location. Even the closest hardware store was three hours away, according to Castillo. There is also limited use of cell phones, because of its proximity to the National Radio Astronomy Observatory (NRAO) located in nearby Green Bank. The construction crew committed to work for two to three months at a time, and stayed on the property.

Craig Swift of the project’s structural engineering firm, Keast and Hood, focused on repairing the metal stud backing. Much of the metal stud cladding wall system had deteriorated, though the primary structural system was in fairly good shape.

By using the versatile EIFS system, it allowed the logo and signage to be built into the building. The front logo letters are up to 2.4 m (8 ft).

By using the versatile EIFS system, it allowed the logo and signage to be built into the building. The front logo letters are up to 2.4 m (8 ft).

Testing—One, two, three
Scott Johnson, an inspector with Williamson & Associates, performed window water testing during phase one and tested windows and claddings related to the openings in phase two. The EIFS, windows, and installation all performed well.

“The building tested out fine,” said Johnson. “There was a major storm during the final phase of construction, with 85-mph [i.e. 137-km/h] winds and hard rain. There were no leaks.”

Johnson and his team conducted ASTM E1105, Standard Test Method for Field Determination of Water Penetration of Installed Exterior Windows, Skylights, Doors, and Curtain Walls, by Uniform or Cyclic Static Air Pressure Difference. This evaluates water infiltration performance, capabilities of windows, and related building construction.

The new primary cream color, with a separate forest green color insert, gives the building a distinct profile and more depth, according to Fillat. This was the first time the architect had ever worked with a drainable EIFS cladding, and he feels it solved this longstanding problem.

After the renovations, residents began noticing drastic changes in their utility bills, with savings of 20 to 50 percent, said Collins.

“There has been a big noise reduction from the outside— most likely due to the ‘air-tightening’ of the building envelope,” he said. “Another benefit is from inside my residence I can no longer hear the wind blowing or have snow in my living room each morning when I wake up.”

Tom Remmele, CSI, is the director technical services/R&D for exterior insulation and finish system (EIFS) producer, Sto Corp. He has held technical management positions in the construction industry for more than 25 years. Remmele is a past Technical Committee chair of the EIFS Industry Members Association (EIMA). He can be reached at tremmele@stocorp.com.

To read the full article, click here.

Detailing Masonry and Frame walls with Continuous Insulation and Air Barriers

Photo courtesy Sto Corp.

Photo courtesy Sto Corp.

by John Chamberlin, MBA

According to the U.S. Department of Energy (DOE), buildings account for 39 percent of total energy use in the United States.1 Efforts to reduce this consumption is reflected in recent changes to building practices and codes.

For example, the DOE has mandated all states update their commercial building codes to meet or exceed American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1-2010, Energy Standard for Buildings Except Low-rise Residential Buildings, by October. Two key requirements of ASHRAE 90.1-2010 are continuous insulation (ci) and a continuous air barrier.

ASHRAE 90.1 defines continuous insulation as “insulation that is continuous across all structural members without thermal bridges other than fasteners and service openings.” Meanwhile, continuous air barriers are defined as “the combination of interconnected materials, assemblies and sealed joints and components of the building envelope that minimize air leakage into or out of the building envelope.”

With these requirements and definitions in place, compliance with ASHRAE 90.1-2010 should be easy. However, this may not be the case.

This map shows the U.S. Climate Zones based on 2009 International Energy Conservation Code (IECC).  [CREDIT] Data courtesy Building Energy Codes Resource Center, Pacific Northwest National Laboratory, U.S. Department of Energy

This map shows the U.S. Climate Zones based on 2009 International Energy Conservation Code (IECC).Data courtesy Building Energy Codes Resource Center, Pacific Northwest National Laboratory, U.S. Department of Energy

Why choose continuous insulation and air barriers?
The biggest problem with many insulated buildings involves thermal bridging. These occur when poor thermal insulator materials meet, creating the path of least resistance for heat to pass through.

An easy example of thermal bridging would be studs in a building’s wall. Even though these studs typically have fiberglass batt insulation between them, the insulation does nothing to reduce the transfer of heat through the stud. Insulation materials include a nominal R-value, which is a measure of the material’s ability to retard heat flow. In theory, a wall assembly constructed with an insulating material of a certain R-value would have a minimum of that material’s R-value as an assembly. However, due to thermal bridging, the assembly’s R-value may be much lower than the R-value of the insulating material itself. This has led to the concept of an assembly’s ‘effective’ R-value versus its ‘nominal’ one.

According to studies conducted by the Oak Ridge National Laboratory (ORNL), thermal bridging in metal frame construction reduces the insulating performance of a wall assembly by 40 to 60 percent.2 For example, a 152-mm (6-in.) metal stud wall assembly including R-19 fiberglass batt insulation may only have an effective R-value between R-8 and R-11. Heating systems for buildings are often designed based on the assembly’s nominal R-value, so in many cases unplanned for energy may be expended to heat a structure’s interior. This is where continuous insulation comes into play.

ASHRAE now requires minimum continuous insulation R-values for buildings based on the climate zones in which those buildings reside. The International Energy Conservation Code (IECC) has identified eight unique climate zones throughout the United States (Figure 1). These zones are determined based on the region’s average temperature, humidity level, and moisture level.

Continuous insulation on an assembly’s exterior, either by itself or in conjunction with interior insulation, is the most economical and efficient way of achieving highly effective R-values. Since ASHRAE 90.1 requires continuous insulation be exempt of thermal bridges, its nominal R-value should be much closer to the effective R-value of the assembly.

This shows a sample detail of a wall assembly featuring a fluid-applied air barrier with continuous insulation under masonry veneer on steel stud backup. Images courtesy Sto Corp.

This shows a sample detail of a wall assembly featuring a fluid-applied air barrier with continuous insulation under masonry veneer on steel stud backup. Images courtesy Sto Corp.

Another major cause of energy consumption is air infiltration and exfiltration. Two of the major air pressures on buildings causing infiltration and exfiltration are wind pressure and stack pressure.

Wind pressure on buildings may have a serious effect on energy and moisture-related air leakage. Since wind pressure is not uniform across a building face, the higher up on a building, the higher the pressure is likely to be, especially as the building rises above objects that might restrict the wind’s flow. Wind pressure pressurizes a building positively on the side it is hitting, but as the wind goes around the corner of the building, it speeds up. This causes the pressure to decrease, and change from positive to negative. These changes in pressure can affect how water moves around the building, especially at corners where water may enter the wall if there is an opening at a joint in the cladding. This phenomenon is known as ‘wind wash’—its effects can be avoided as long as the air barrier is intact at the corners.

Stack pressure occurs when there is a difference in atmospheric pressure at the top and bottom of a building. This difference is the result of a variance in temperature at the top and bottom, causing varying weights of the columns of air inside the building compared to outside. In climates where the interior is heated, stack pressure may cause air infiltration at the bottom of a building and exfiltration at the top. In climates where the interior is cooled, exfiltration may occur at the bottom and infiltration at the top. Stack effect can be controlled by designing airtight vestibules, closing off openings (i.e. mechanical penetrations) between floors, and sealing vertical shafts within the building.

Air barrier systems help control air infiltration and exfiltration in buildings. These systems accomplish this by sealing joints, penetrations, and openings to create an airtight assembly. This, combined with venting and compartmentalizing, allows pressure to equalize between the interior and exterior of a structure. Without these differentials, air infiltration and exfiltration is restricted.

Air barrier systems should meet three key criteria:

  1. They should be continuous to not allow opportunities for air leakage.
  2. They should be structural, or in other words, permanently secured to the supporting structure. (Air barriers must be able to withstand wind pressure, stack pressure, and any pressure caused by mechanical effects, and ultimately transferred to the structure. If not a permanent part of the structure, air barriers may tear or displace under stress.)
  3. Air barriers must be durable. (They are typically installed behind a building’s cladding and may require removal of the cladding for any type of maintenance or repair. For this purpose, a highly durable air barrier will always be preferred so maintenance can be avoided.)

Benefits of continuous insulation and air barriers
A study conducted by Morrison Hershfield, “Energy Conservation Benefits of Air Barriers,” focused on the inclusion of both continuous exterior insulation and a continuous fluid-applied air barrier. Using 3D modeling, a prototype medium three-story office building was proposed for Dallas, Seattle, and Toronto climates. Baseline case buildings were set up to meet the minimum requirements of ASHRAE 90.1-2007 for newly constructed buildings.

The installation of fluid-applied air/moisture barrier using spray equipment over sheathing.

The installation of fluid-applied air/moisture barrier using spray equipment over sheathing.

According to the report:

Heating, cooling, lighting, and interior equipment energy consumption were modeled for each load case at 10-minute intervals and the results are summarized on a monthly usage basis in units of kilowatt hours (kWh). This data was then used to calculate energy savings over the base case, and an annual carbon equivalent was calculated based on the annual heating and cooling costs.3

The modeling determined that in terms of energy efficiency, the inclusion of a continuous air barrier actually had a greater impact than the continuous insulation. Annual energy cost savings ranged from $5000 to $19,000, compared to the baseline building which included continuous insulation by itself. Also, there was a diminishing return in energy cost savings as the R-value of the continuous insulation was increased.

The challenges with continuous insulation
The difficulty that arises with continuous insulation is ironically similar to the phenomenon that makes it necessary in the first place. The definition of continuous insulation explains it must be “continuous across all structural members without thermal bridges other than fasteners and service openings.”

In this case, ‘fasteners’ refers to materials such as nails and screws. What this definition does not account for are common details such as ties and shelf-angles in masonry construction or clips and z-grits (i.e. horizontal structural member providing lateral support to the wall panel) in non-masonry cladding assemblies.

In a recent paper prepared by RDH Building Engineering Ltd., entitled “Thermal Bridging of Masonry Veneer Claddings and Energy Code Compliance,” 3D-thermal modeling was used to determine the effects these types of details might have on the effective R-value of a wall assembly including continuous insulation. This value would change based on the actual construction assemblies and structure size. According to RDH:

metal cladding support connections occupying less than 0.5 percent and even less than 0.05 percent of the wall’s surface area can have a profound impact on effective R-values (i.e. anywhere from 10 percent to greater than 50 percent).4

Using masonry construction as an example, RDH goes on to explain different types of masonry ties (e.g. steel versus fiber) and various backup materials (e.g. wood stud, concrete, or steel backup) also have an impact on the degree of thermal bridging that may take place.

Continuity of the air barrier is maintained at a transition from sheathing to foundation through the use of a flexible transition membrane embedded in a fluid-applied air/moisture barrier.

Continuity of the air barrier is maintained at a transition from sheathing to foundation through the use of a flexible transition membrane embedded in a fluid-applied air/moisture barrier.

Due to their low insulative value, steel masonry ties may reduce the insulation effectiveness by five to eight percent, depending on the type of steel and backup materials. Even more impactful, direct attached masonry shelf angles may reduce the effective R-value by 40 to 55 percent in conjunction with typical exterior insulation thicknesses and steel masonry ties.

Another study by Morrison Hershfield, “Thermal Performance of Building Envelope Details for Mid- and High-rise Buildings,” looked at 40 common building design envelope details and again used 3D modeling to determine the effect thermal bridging might have on the overall thermal efficiency of buildings including continuous exterior insulation.5

This study noted the addition of more materials with higher insulating values did not greatly improve the overall thermal performance of the wall assembly so long as these thermal bridges existed. It also points out quite clearly that even in buildings including continuous exterior insulation, all thermal bridges must be considered to determine a structure’s overall thermal efficiency.

Continuous air barrier challenges
There are numerous products that qualify as air barriers including:

  • building wraps;
  • fluid-applied barriers;
  • interior drywall;
  • sprayed polyurethane foam (SPF);
  • extruded polystyrene (XPS) insulation boards;
  • self-adhered membranes; and
  • polyethylene sheets.

These products help prevent air leakage. If it was possible to construct buildings out of one material, and in a vacuum, any of these would work as an air barrier.

Unfortunately, buildings are constructed out of thousands of different parts assembled together in climates with changing weather patterns, temperatures, and pressures. For an air barrier system to be continuous, it needs to be able to address joints and seams where sheathing materials meet.

Transitions between dissimilar materials must be taken into account. For example, there is the transition from the sheathing of a building to its foundation. Air barrier products should be able to bond structurally to multiple types of substrates as well as being durable enough to bridge transitions where substrates may be out of plane with one another. Movement joints are included in buildings to account for anticipated expansion and contraction. As a result, the air barrier system should also be able to accommodate expansion and contraction.

These air barrier products are also going to be subject to thermal changes that will cause additional stress on the materials during the building’s lifespan. The result is products such as kraft papers and building wraps may ultimately tear or pull away from the building. Other products like common joint tapes or self-adhered membranes may lose adhesion if not properly installed, causing discontinuity of the air barrier and potentially creating opportunities for moisture to intrude. If air barrier systems do not account for the same stresses the building will experience, then they may not only lose effectiveness, but can also actually create problems within the wall cavity that may not be detected until extensive damage has already been done.

The aging Lido Beach Towers (Long Island, NY) were retrofi tted with an exterior insulation fi nish system (EIFS), resulting in a more than 30 percent energy saving.

The aging Lido Beach Towers (Long Island, NY) were retrofitted with an exterior insulation finish system (EIFS), resulting in a  more than 30 percent energy saving.

The construction of an airtight building envelope greatly reduces the risk of moisture problems as a result of air leakage and condensation. However, airtight construction may be less capable of drying than air-porous construction in the case of water leakage or other unplanned circumstances that might allow water to enter the wall assembly.

Water is able to penetrate the building envelope through numerous means. For example, wind may drive rain through incidental cracks or holes in the building’s cladding, or capillary action in porous materials, cracks, or holes may draw water toward the interior. Further, water vapor may be transported by air or diffusion that can condense on cold surfaces within the building envelope.

As mentioned, there are various products that may be classified as air barriers, but not all of them can be classified as water-resistive barriers (WRBs). In fact, the International Building Code (IBC), International Residential Code (IRC), and IECC have specific requirements that must be met for these products to qualify as both an air barrier as well as a water-resistive barrier.

In the case of air barriers, an individual product will be tested according to ASTM E2178, Standard Test Method for Air Permeance of Building Materials. Further, WRBs must meet ASTM D226, Standard Specification for Asphalt-Saturated Organic Felt Used in Roofing and Waterproofing, if they are to be considered waterproof.

Common tests, such as American Association of Textile Chemists and Colorists (AATCC) 127, Water Resistance: Hydrostatic Pressure Test, measure a product’s ability to resist water penetration under adverse conditions, such as wind-driven rain, which is simulated by placing the product under hydrostatic pressure.

Traditionally, asphalt-saturated felt, kraft waterproof building paper, or building wraps have been used as the moisture protection component of wall construction. Installing these types of barriers usually involve shingle-style lapping and mechanical fastening to the sheathing with nails, screws, or staples. While these installation methods are common, because they disrupt the continuity of the air and water-resistive barrier, they actually provide opportunities for air leakage and moisture intrusion.

The best choice for an air and water-resistive barrier is one that meets a number of durability requirements and is able to resist wind and rain loads. Common criteria to look for include:

  • resistance to puncture, pests, and low-sustained negative pressure from building stack effect and HVAC fan effect;
  • ability to withstand stress from thermal and moisture movement of building materials and stress from building creep; and
  • resistance to mold growth and abrasion.

Fluid-applied barriers are gaining popularity in both commercial and residential construction due to their ability to form a full monolithic barrier, as well as their durability and ease of application compared to a traditional wrap or paper product. Many of these products act as both an air barrier and a water-resistive barrier.

Queen’s Landing condominium community in Kent Island, MD, was also retrofi t with an energy-effi cient EIFS assembly. Some of the EIFS installations included a secondary water/air management system, while some were fi t with a hybrid stucco system.

Queen’s Landing condominium community in Kent Island, MD, was also retrofit with an energy-efficient EIFS assembly. Some of the EIFS installations included a secondary water/air management system, while some were fit with a hybrid stucco system.

Fluid-applied barriers are generally rolled or sprayed onto sheathing or concrete masonry unit (CMU) backup and fully adhere, becoming part of the structural wall. Some manufacturers use adhesion testing, such as ASTM C297, Standard Test Method for Flatwise Tensile Strength of Sandwich Constructions, to verify a full bond between the barrier and the substrate. It is often found the adhesion may actually exceed the strength of the substrate itself. However, this is not the case with paper-type products where material may tear or blow off the building, or with self-adhered membranes where a loss of adhesion may cause edge peeling or a loss of the barrier altogether.

As fluid-applied barriers are initially in liquid form, there is no lapping of materials that can create discontinuity of the barrier. Once a fluid-applied barrier is completely installed on a building’s wall, the material acts as a single monolithic barrier. Fasteners such as nails, screws, and staples are not needed to apply fluid-applied barriers, so additional holes where rain can enter are less of a concern. Also, because fluid-applied barriers may be rolled or sprayed, the possibility of installation error is greatly reduced. Proper installation of paper-type products and self-adhered membranes frequently require cutting, folding, and use of special tools and accessories. Improper installation of these barriers can be costly and time-consuming to correct; all too often, these important details may be ignored altogether.

Conclusion
Plenty of research has been done to show the advantages of continuous insulation and air barriers. The inclusion of these elements in new construction should help enhance the overall energy efficiency of buildings and allow owners to realize energy cost savings as well. For design professionals, however, the task of creating an energy-efficient building may be just as difficult. New products and new resources are being developed every day to make this task easier, but in the meantime, the key point to remember is with both continuous insulation, as well as continuous air barriers, the details must be carefully considered to realize maximum energy efficiency.

Notes
1 For more, see U.S. Department of Energy (DOE) 2008, Buildings Energy Data Book. This resource was prepared for DOE’s Office of Energy Efficiency and Renewable Energy (EERE) by D&R International. (back to top)
2 For more, see “Thermal Performance of Steel-framed Walls,” by E. Barbour, J. Godgrow, and J.E. Christian, published by the national Association of Home Builders (NAHB) Research Center in 1994. (back to top)
3 See Morrison Hershfield’s “Energy Conservation Benefits of Air Barriers–StoGuard: The Effect on Energy Conservation,” by Chris Norris. (back to top)
4 See G. Finch et al.’s “Thermal Bridging of Masonry Veneer Claddings and Energy Code Compliance.” The proceedings are taken from 12th Canadian Masonry Symposium, held in Vancouver, B.C. in 2013. (back to top)
5 See the Morrison Hershfield report, 1365-RP, “Thermal Performance of Building Envelope Details for Mid- and High-rise Buildings.” (back to top)

John Chamberlin is product manager for StoGuard and StoEnergy Guard at Sto Corp; these divisions are focused on heat, air, and moisture management within the building envelope. Prior to this position, he served as product manager for StoCoatings and as associate product manager for StoPowerwall and StoQuik Silver. Chamberlin earned a Master’s in Business Administration at Atlanta’s Emory University and is a graduate of the University of Tennessee, with a Bachelor of Science degree in Marketing. He can be reached by e-mail at jchamberlin@stocorp.com.