Overcladding masonry facades: Additional practical insights

by arslan_ahmed | July 24, 2023 11:00 am

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By Albert Aronov, AIA

The March 2023 issue of Construction Canada included an article[2] from the author on the topic of overcladding as a solution for owners of commercial, institutional, and government buildings 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, with respect to overcladding of masonry 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.

The essential role of air barriers in the overcladding assembly

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 vapour 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 esthetic 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 vapour-permeable barrier, with a mini-cavity and drainage mat for moisture to escape. This approach results in a waterproof, breathable, and attractive facade.

For projects in cold climates using a rainscreen system instead of a face-sealed solution—whether fibre 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. Experts such as John R.S. Edgar, president of the EIFS Council of Canada, emphasized the placement of ci “outbound of the studs,” adding:

Canadian code-writers have taken note—the National Energy Code for Buildings’ (NECB’s) focus has shifted to the building envelope’s passive performance, limiting reliance on powered mechanical systems in the alternative path options.¹

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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, as long as the ci is installed on exterior side of the vapour barrier. The reverse—heavy interior insulation and little or none outside—lead to condensation occurring on the inside, and the potential for mould 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), in order 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 vapour as well as heat, or lack of it.

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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 vapour 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.

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Teams considering using EIFS for a masonry overcladding application may refer, for example, to the EIFS standards originally published in 2009 and 2010 by the Underwriter’s Laboratories of Canada (ULC). According to the EIFS Council of Canada, the ULC standards have made “the use of a water resistive barrier (WRB) system with EIFS to create a drained cladding assembly over moisture sensitive substrates … a standard requirement for all EIFS applications.”  Any moisture that may penetrate through failed sealants or through cracks or flaws within the applied system can become 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 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—combining elements of systems from different manufacturers can lead to unexpected and sometimes unsuccessful results.

Structural questions and budgetary 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.

For rainscreen-style overcladding systems—whether insulated metal panel, panelized EIFS, terra cotta, or fibre 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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Choosing the right overcladding approach: Face-sealed system considerations

Regarding assembly design for management of water vapour 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 that 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 the majority of climate regions, whether conventional metal panels, fibre cement panel, or EIFS.

Notes

¹ See the article by John R.S. Edgar, “Improving Continuous Insulation,” Construction Canada, November 14, 2016, www.constructioncanada.net/improving-continuous-insulation/[8].

² Read the paper by Anis, Wagdy, FAIA, “Air Barrier Systems in Buildings,” published online by the Whole Building Design Guide (WBDG), www.wbdg.org/resources/air-barrier-systems-buildings[9].

³ Visit the EIFS Council of Canada, EIFS Practice Manual, Version 1.0, p.13, www.exteriors.ca/holt001.pdf[10].

[11]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.constructioncanada.net/overcladding-masonry-facades-additional-practical-insights/

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