Additional practical insights on overcladding masonry facades

by arslan_ahmed | August 24, 2023 4:00 pm

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By Albert Aronov, AIA

The November 2021 issue of The Construction Specifier included an article from the author on the topic of overcladding as a solution for commercial, institutional, and government buildings owners that are structurally composed of masonry and beginning to show the impacts of age, weather, neglect, and deferred maintenance on the enclosure. This is a follow-up article speaking to additional questions in this system type. The topics to be addressed in this article, when it comes to overcladding masonary facades and foundations, as well as roof assemblies, include the following:

• Placement and attachment of insulation and air barrier within the assembly.
• Considerations for the use of exterior insulation and finish system (EIFS) overclad solutions.
• Structural considerations, including thermal bridging and construction costs.
• The appropriateness of face-sealed systems in certain climate regions.
• Questions regarding air barriers.

Insulation and air barriers

One premise of the original article is that the bearing walls of many government and school buildings across North America, built in the last century with solid masonry, are now experiencing moisture intrusion. These areas of leakage and incursion are leading to severe degradation and damage to brickwork, window openings, and interior assemblies with plaster and other finishes. As an alternative to removing and replacing the original masonry—an approach that can negatively impact structural integrity—project teams and architects are encouraged to design an insulated facade layer with vapor barrier, creating a new enclosure that is watertight and energy efficient, and possibly more attractive. This raises a question about how to ensure the ideal placement and attachment of the insulation, air barrier, and cladding.

The project case studies in the original article were school buildings built in the early part of the 20^th century with masonry, and particularly brick and brick veneer. The approach employed for these structures has been intended to accomplish restoration and renovation using a face brick system that would improve the enclosure performance while retaining the original aesthetic in some measure. In these cases, the new face brick overcladding was applied directly to the existing load-bearing masonry (after any needed repairs) without adding any layers of insulation between. The technique includes parging the original masonry to create a smooth surface for application of a fluid-applied vapor-permeable barrier, with a mini-cavity and drainage mat for moisture to escape. This approach results in a waterproof, breathable, and attractive facade.

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For projects in cold climates using a rainscreen system instead of a face-sealed solution—whether fiber cement, metal panels, terra cotta, or siding—insulation is essential and must be continuous to be most effective. The International Energy Conservation Code (IECC) adopted a requirement of continuous insulation (ci) in the building enclosure in 2012 because of its effectiveness in increasing thermal resistance of a wall. However, even if it were not required, inclusion of CI in the exterior overcladding system represents an opportunity for optimizing energy efficiency for the balance of the building life span. In a case study presented at Building Enclosure Science and Technology (BEST5) Conference, on overcladding a critical-care patient tower for a Baltimore, MD hospital, the authors noted:

Without a continuous insulation system in the masonry cavity the concrete masonry units of the backup wall and the edge of the concrete floor slabs became major contributors to heat loss due to thermal bridging…With the exterior assembly uninsulated, the interior framed wall realized heat loss through thermal bridging due to the metal studs exposure to the uninsulated concrete masonry units…¹

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In addition, the exterior CI can prevent issues related to condensation and moisture. Many dew point calculations in rigorous building science studies have proven that walls with no insulation between studs and using only exterior ci are fully protected from air leakage condensation during cold weather, if the ci is installed on exterior side of the vapor barrier. The reverse—heavy interior insulation and little or none outside—lead to condensation occurring on the inside, and the potential for mold and rot with the attendant structural deterioration and occupant health risks. For overcladding scenarios, rainscreen systems provide the best opportunity for including ci.

Important air barrier considerations

The purpose of an air barrier is to stop airflow or resist air pressure within the enclosure (or between conditioned and unconditioned spaces) to control the flow of heat and moisture. As such, any air barrier must be continuous and durable, with all transitions and penetrations carefully sealed. Unchecked air movement creates both moisture management problems and thermal performance issues, since air carries moisture and water vapor as well as heat, or lack of it.

With respect to overcladding masonry, the act of repairing and smoothing the existing wall by parging, as well as by tending to and sealing cracks in masonry and mortar, results in an enhanced air barrier function. This is further improved with the installation of a fluid-applied vapor barrier within the overclad assembly, creating an additional impediment to the movement of moisture through the system. To state plainly, the air barrier is not a single component of the enclosure assembly. When thinking of the air barrier, one should think about the flow of air through the assembly in total, as an integrated system.

How much air should pass through the enclosure? Typically, the answer is none. To the definition that an air barrier should be continuous, structural, and uninterrupted, according to Wagdy Anis, FAIA, writing for the Whole Building Design Guide. As he stated, the enclosure and the overcladding layer should address three types of air leaks through an architectural enclosure:

1. Orifice flow, e.g. in a slit unintentionally left between a window rough opening and its frame.
2. Diffuse flow, such as through some brick or concrete block.
3. Channel flow, the common type of air leaks where the air entry point and exit point are distant from each other, giving the air enough time to cool below its dew point and deposit moisture in the building enclosure.²

Taken together, these principles help to effectively design and specify overcladding for one of the most common challenges faced by long-term building owners: poorly performing and unattractive masonry walls. Failure modes in masonry facades where the masonry wall is supported from steel lintels begin with age alone and can be exacerbated by older practices, such as missing or ineffective masonry expansion joints. Some cavity wall construction may lack thermal insulation as well.

Thermally displaced masonry will result from the lack of expansion joints, which may be visible in brick facades. In extreme cases, these may impact glazing systems. Some exterior walls may not even comply with modern codes for resisting lateral imposed loads.

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Questions about EIFS overcladding

The original article also included some discussion of exterior insulation and finish system (EIFS) applications as an effective and frequently utilized approach for face-sealed overcladding to address aging or inadequately designed masonry facades. However, there is an interest in knowing whether there has been any skepticism or criticism of this approach among industry professionals, whether based on the technique or performance outcomes. The best answer is, there should be, depending on the particular EIFS product and application techniques utilized.

First developed and marketed in the 1970s, this once novel system has evolved quickly with greatly improved efficacy in more recent iterations. There continue to be some contractors and trades groups in the marketplace who may incorporate outdated systems and products in their solutions offered, but these must not be used for exterior overcladding of masonry in part because some of those systems provides no means for moisture management, including draining or drying of the system.

Teams considering using EIFS for a masonry overcladding application should refer to ANSI/EIMA 99-A-2017, Standard for Exterior Insulation and Finish Systems (EIFS) and EIFS with Drainage. According to the EIFS Industry Members Association (EIMA), the standard outlines “the generic materials, details, and design considerations for EIFS and EIFS with drainage,” noting that building professionals should consult manufacturer product literature for specifications, application instructions, and specific details. Thorough attention to the above will help avoid moisture penetrating through failed sealants or through cracks or flaws within the applied system and becoming trapped, creating deleterious conditions.

Water penetration must be mitigated with drainage and drying, and that is what newer EIFS systems are designed to do: drain and dry. This makes properly designed, applied, and assembled modern EIFS products highly effective as overcladding solutions for structural masonry. It is an adaptable approach that can succeed regardless of texture, joint design, and fenestration detailing, with benefits ranging from elimination of water penetration to enhanced wall R-value.

Building teams should keep in mind the success of this approach hinges on a sound masonry wall, parged smooth, and free of contaminants. As outlined in the ULC’s EIFS Standards, attempts to apply EIFS to masonry that is crumbling, spalling, loose, or cracked will likely result in system failure. Contractors and trades should consult the standards for all requirements of a successful application including dryness, temperature, substrate flatness and, perhaps most importantly, compatibility. It is important to note that combining elements of systems from different manufacturers can lead to unexpected and sometimes unsuccessful results.

Structural and budgetary questions and concerns

With respect to the solid masonry school buildings which are overcladded with face brick, the design solution and detailing typically includes creating
a brick shelf to support the face brick with modifications to the existing stone base. Above the first floor and grade level, where the new cladding must be attached directly to the existing backup wall, new relieving angles are attached to the load-bearing masonry wall to support the face brick. Note that structural engineers must verify the load-bearing capacity of the existing foundations and walls. Also, the design must consider the potential for the brick to expand, which can create tension and interactions with the attachment assembly.

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For rainscreen-style overcladding systems—whether insulated metal panel, panelized EIFS, terra cotta, or fiber cement board—the system generally is supported by a light-gauge metal subframe of either galvanized steel or aluminum. The subframe is cantilevered from the backup with a rail system
or with adjustable brackets. In consultation with structural engineers, the sub-framing system must be designed to address dead load, wind load, seismic concerns, thermal expansion and contraction, and deflection for different backup conditions.

Regarding cost impacts, masonry overcladding solutions tend to be driven by budget-conscious solutions. For this reason, variations in costs associated with particular products or assembly components tend to be marginal, in the author’s experience.

Moving onto thermal bridging, metal frames, brackets, and rail systems do carry the potential for thermal transfer. Metal brackets and subframes attached directly to the masonry backup tend to conduct cold temperatures, contributing to the building’s heat loss. For these reasons, many manufacturers produce components made from low-thermal-conducting metals, and systems incorporated with thermal breaks. Whether or not the building team specifies products from one of these manufacturers, it is critical to design an assembly that includes thermal breaks in the subframe system to avoid thermal bridging, and to enhance the enclosure’s thermal performance.

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Face-sealed systems and climate region appropriateness

Regarding assembly design for management of water vapor and moisture, it is important to consider whether face-sealed systems are appropriate as an overcladding solution in any climate region. Whether a given face-sealed solution is stucco, EIFS, or system such as metal paneling with joints sealed with caulk or similar, these systems for exterior overcladding create challenges for enclosure design teams, who understand there must be a way for moisture to drain or dry—as they are not ideal in most climates.

The recommended and appropriate uses of face-sealed overcladding systems would be generally for low-rise buildings in very or relatively dry climates with lots of sun and little rain. Even in these scenarios there could be benefits for designing and specifying one of the open, drained system types recommended for many climate regions, whether conventional metal panels, fiber cement panel, or EIFS.

Notes

¹ See the article by McKelvey, Wilson, Copley, and Foster, “A Sustainable Repurposing of the Aging Facility,” published by BEST5 Technical Committee, April 16, 2018, www.brikbase.org/content/sustainable-repurposing-aging-facility.

² Read the paper by Anis, Wagdy, FAIA, “Air Barrier Systems in Buildings,” Whole Building Design Guide, www.wbdg.org/resources/air-barrier-systems-buildings.

³ Visit the EIFS Industry Members Association, “Standards,” www.eima.com/technical/standards.

Author

Albert Aronov, AIA, is a partner with RKTB Architects, P.C. Aronov specializes in building restoration, as well as new construction in the academic, residential, and commercial sectors. He has led his firm’s education studio since 2004.

Source URL: https://www.constructionspecifier.com/additional-practical-insights-on-overcladding-masonry-facades/

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