Exterior Wall Assemblies: Are you getting what you specified?

by Molly Doyle | April 7, 2014 1:30 pm

[1]

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 [2]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.

[3]

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.

[4]

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.

[5]

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.

[6]

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.

[7]

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 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[8],” by Joseph Berchenko AIA, CSI, CCS. (back to top[9])

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[10].

Source URL: https://www.constructionspecifier.com/exterior-wall-assemblies-are-you-getting-what-you-specified/

---