Overcladding for old masonry façades: Why it is important to think performance first

by brittney_cutler | November 3, 2021 8:00 pm

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By Albert Aronov, AIA

Older masonry structures from many eras, including libraries, town halls, commercial blocks, and school buildings, stand at the geographic center of many communities, holding symbolic meaning and serving varied needs and purposes. As they age, many begin to show the effects of neglect, weather, and deferred maintenance on their façades, foundations, and roof assemblies.

While some historic enclosures merit careful restoration, in other cases they simply need to be renovated and modernized for the long-term. Commercial, institutional, and government owners are increasingly turning to façade overcladding as one solution for poorly performing brick, stone, and stucco clad buildings.

Investing in smart, context-sensitive overcladdings—as well as upgrading older masonry buildings with new, energy-wise envelope improvements—can contribute to not just better buildings but also improved neighborhoods.

From Portland, Maine to Portland, Oregon, many cities are contending with government and school buildings from the last century, built with solid masonry bearing walls.

“Many are leaking,” according to Carmi Bee, FAIA, of RKTB Architects. “The resulting degradation can be severe, damaging to brickwork, window openings, and interior plaster walls.”

Instead of removing original masonry, which can affect structural integrity, the architects can design a new insulated façade layer and vapor barrier, making the enclosures watertight, energy efficient, and attractive. Examples include a 1907 school in Queens, New York, where a team at RKTB Architects including Bee designed and specified a restoration of the original architectural features lost over time while protecting the interiors from moisture degradation with an overcladding system of a parge coat, moisture barrier, drainage mat, and new face brick recapturing the original school’s silhouette.

What is Overcladding?

Overcladding is not consistently defined across the architecture, engineering, and construction (AEC) fields, but it generally means a performative layer added to an existing building, not a decorative or purely aesthetic exterior treatment. Like a reroof overlayment, adding new envelope construction over existing masonry, concrete, brick, and other façade materials presents an effective and desirable approach for revitalizing building façades in reconstruction projects.

The approach offers the opportunity to incorporate new aesthetic materials, additional insulation, and even air barriers and moisture control layers often required by authorities having jurisdiction (AHJs) or owner/client groups. In some cities such as New York and Toronto, in fact, new green codes are incentivizing the use of overcladding to improve building energy performance without penalizing the owners for exceeding limits on added floor area ratios (FARs).

Two effective and common approaches to overcladding are exterior insulation and finish system (EIFS) applications and the hanging of insulated metal panels (IMPs) on a new outer subframe or furring. EIFS, a relatively new system type introduced in the United States market in the early 1970s, provides an adaptable opportunity for overcladding, insulating, and waterproofing on older or poorly designed masonry façades, regardless of texture, joint design, and fenestration. Successful applications hinge largely on having a sound masonry wall beneath. Benefits of the EIFS overclad include the elimination of water penetration as well
as improvements to wall R-value.

As for IMPs, there is a growing field of examples showing effective overcladding with metal panel products. The Metal Construction Association (MCA) has contended that varied overcladding approaches—from insulated rainscreens to backup walls to metal profiles and other panel assemblies—work well over varied substrates as well as steel or concrete structures. They also provide an effective barrier, delivering continuous insulation (ci) across overclad areas. Retrofit wall applications commonly use metal panels or IMPs hung on an existing exterior surface such as CMU or brick veneer.

In this way, overcladding shares characteristics with rainscreen systems, and overclad enclosures can be considered as rainscreens in design and construction evaluation. It allows building exteriors to be updated even in load-bearing segments of concrete and masonry walls without having to undertake expensive reinforcing of structure and additions of columns and beams or underpinning foundation.

According to the Center for Window and Cladding Technology (CWCT), “a rainscreen cladding system consists of a plane of panels designed to protect the wall from rain. It may be constructed as overcladding supported on a brick or block wall or as an integral wall supported from mullions or studs spanning from floor to floor.”

The CWCT also notes rainscreen overcladding often works effectively as part of building rehabilitation projects. In these solutions, the rainscreen walls are supported from framing members with a second inner barrier wall assembly that carries wind load and provides for requisite air permeability.

Early experience with overcladding in cities such as Toronto proved highly effective. Kevin Day, a project principal with Sense Engineering, says this success led to “a movement to facilitate the renewal of high-rise residential buildings” in Canada and elsewhere. Whether the architect uses insulated composite exterior metal panels or another rainscreen-type overcladding, the solution “can improve not only the performance of the building, but also the comfort of the occupants.”

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Principles and Precepts

While this kind of overcladding is an extensive project, it offers several attractive benefits: thermal performance and air tightness are significantly improved, helping eliminate moisture and condensation issues. In addition, overcladding can boost desirable acoustic isolation and attenuation. Properly executed, overcladding can also optimize the use of a masonry enclosure’s thermal mass. It can add decades to the structure’s service life expectancy without decreasing room sizes, as with interior façade stabilization and insulating options.

Specific considerations for façade overcladding approaches are like those for any retrofit of the enclosure assemblies that are predominantly masonry, including bearing walls and brick veneer. Design goals include:

• Increasing thermal performance;

• Providing an air and water barrier;

• Providing fire/smoke containment to enhance
building resilience;

• Modest costs and short design and construction schedules;

• Allowing building to be largely occupied and accessible during construction; and

• Limiting disturbance to occupant or tenant operations.

Another critical consideration is the retrofit approach should allow the limiting of overcladding system weight to stay below structural framing load capacities. Typical limits for steel-framed, masonry veneer systems, for example, would be about five percent of the dead load threshold for steel structural members, and 10 percent of building lateral loads.

Done well, overcladding will improve building aesthetics with relatively minimal impacts to occupants during installation. Green retrofit projects and building rehabilitations should be designed to tighten up the building envelope for better thermal efficiencies, not to mention dramatically reduced air and moisture infiltration. Overcladding options include energy-efficient insulated wall systems, silicone sealant and gaskets for glazed areas, new air and vapor barriers transitioning into window openings, and the sealing of all window-wall interfaces.

But where does one start? For example, how much insulation is required, and where should the vapor barrier be located? What are the benefits and disadvantages of overcladding for masonry assemblies? Good questions, and the project team should start with the basics, as a pioneering enclosure guru, the late Wagdy Anis, would say: heat, air, and moisture, or HAM.

Heat (and cold)

Overcladding, as with all enclosure design opportunities, hinges on climate. The climate zone will dictate many of the design choices, such as the location of air and vapor barriers. The building configuration and orientation and the local site’s topography, prevailing winds, external shadowing, and direct sunlight will determine the enclosure needs during both heating and cooling seasons. In all climates, continuous insulation is important—the insulating layer should not be interrupted by structural members or thermal bridges, such as metal elements that extend from the building interior through the insulation layer to the exterior. Thermal breaks at window frames, for example, ensure effective ci.

Project teams can use Building information modeling (BIM) models or U-value calculations to determine enclosure properties. Another option is the Simplified Building Energy Modeling (SBEM) calculation methodology, a national standard used to determine the energy efficiency of commercial properties. The methods allow project teams to evaluate heat flows and the overcladding design’s impact on energy performance. Variables include window-wall rations (WWRs), insulation levels and barrier types, use, and location.

Moisture

Water vapor in the air as well as bulk moisture must be addressed in the overcladding design. Rainscreen-type overcladdings drain behind the exterior finished wall, while barrier enclosures such as EIFS drain at the exterior plane. The chosen building overcladding application should balance moisture inside and outside the building, as well as allow the building and the enclosure assemblies to dry out. Moisture accumulation inside the building and within the enclosure should be offset by equivalent drying.

One concern for over overcladding is the potential for trapping excess moisture within the building but also within the enclosure assembly itself, for example between the new exterior cladding and the original masonry walls. To limit the negative effects of excessive condensation—which can lead to oxidation, deterioration of building materials, and potential mold occurrence—the project specifiers and architects should designers determine how much water vapor could be generated within the building and determine the resultant increase in internal vapor pressure above that of external air. After that determination, assess the performance expectations and physical properties of the enclosure assemblies.

Air

How much air should pass through the enclosure? More often, the answer is none. The air barrier should be continuous, structural, and uninterrupted. As Anis himself wrote in the Whole Building Design Guide, the enclosure and the overcladding layer should address three types of air leaks through an architectural enclosure:

1. Orifice flow, such as 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.”

The issues of unchecked air movement also create moisture management problems since air carries moisture and water vapor.

Taken to together, these HAM principles advanced by Anis 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 façades 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, too.

Further inspection may reveal aging flashings and the use of parged cementitious coating on concrete masonry unit (CMU) as an air barrier. Thermally displaced masonry will result from the lack of expansion joints, which may be visible in brick façades. 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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Overcladding for Performance

These solutions are complicated and challenging to explain to stakeholders who are not building professionals. But once the project team has the confidence of decision-makers, a community will be able to enjoy a piece of its legacy, an iconic architectural landmark, for decades to come. After all, in addition to providing the setting for teaching and learning, school buildings in many cities and towns are frequently places where residents of those communities go to vote, attend meetings of various kinds, gather for social and cultural events, and participate in other types of civic engagement.

Masonry strengthening, façade overcladding, and targeted expansions represent cost-effective approaches to making the most of existing K-12 facilities, university buildings, civic structures, and older commercial and residential architecture. The approach can benefit a wide and diverse group of users. They can also contribute to improved neighborhood cohesion, helping to celebrate and build upon the legacy of each existing or historic building.

Case Studies: Urban Public Schools

These conditions may be seen in older school buildings around the country. Unfortunately, the combined forces of time, climate, and lagging maintenance can leave school districts’ facilities teams with significant, and often unexpected challenges. Schools typically age faster than funding to fix them is allocated.

For some municipalities, this leads to a continuing cycle of each newly composed school board deferring addressing the problem to the next one, while student populations change and expand, and the natural wear-and-tear process accelerates. For officials to address the deleterious effects of time, weather, and full occupancy on masonry school buildings, overcladding has emerged as a valuable strategy. The relatively simple, energy-conscious façade upgrades can be accompanied by replacements of outdated, thermally inefficient windows. As many older, masonry load-bearing walls are today degrading considerably, now porous and leaking, the damage to brickwork, window openings, and interior plaster walls can be severe.

Complicating the rehabilitative projects are issues mandated by building, energy, and life-safety codes. Replacing masonry is typically not going to be an option—and even when it is possible, it can lead to an unappealing patchwork look that inspires little confidence in the community the school serves. Instead, overcladding wraps the entire masonry façade with a new, performative outer layer that allows the introduction of more modern architectural thinking to older schools.

The following example is one approach to façade over-cladding at P.S. 73 in Brooklyn, New York. Built in the late 19th century, the aging brick façade of this remarkable school building had naturally begun to weaken after more than 100 years of service. A site visit by architects revealed the original copper cornices were deteriorated and gone, and pieces of brick and mortar were working their way loose, presenting a potential hazard to passersby. These were red flags, and a project team began to address the issue.

To rehabilitate the structure, the designers working with School Construction Authority (SCA), or New York City recreated some of the original architectural components, matching them exactly to produce a cohesive look that honors the familiar and locally beloved school. Apart from these cosmetic approaches, a considerable amount of effort went into the use of grout injection technology to strengthen the aging masonry from within. Filling every void and hairline crack, the hydraulic lime grout has enhanced the structural integrity and prevented future damage from penetration by moisture.

In another example, P.S. 88 in Queens, New York, a 1907 facility required a means for improving the energy performance of its enclosure while returning distressed and discolored architectural details to some measure of their former glory. Over the decades some architectural features had been removed, including the original parapets, cornices, and other neoclassical detail. At the same time the rehabilitation project would have to address the severe moisture damage to the academic spaces inside revealed by a site survey, to protect students and staff from mold and other moisture-related health hazards. The project team tested exterior walls to determine the amount of water ingress and relative structural integrity, inspecting the headers, wood window jambs, interior clay tile, and plaster finish.

The building was determined to be an ideal candidate for façade overcladding. The existing wall could be treated with an exterior parge coat and moisture barrier, followed by a drainage mat. Last, a new brickface would be installed in a color and style to match the original masonry deemed strong enough to support the addition. The overclad stabilized the school building and extended its service life. At the base, cast stone masonry replicas preserved the building profile, and lookalike cast-stone headers are installed over existing, rehabilitated steel. Durable windowsill upgrades include flashing and sub-sill pans, and the parapet, stripped of its original character over time, has been rebuilt with concrete curb and hung with an ornamental cornice composed of glass fiber-reinforced concrete (GFRC).

Author

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

Source URL: https://www.constructionspecifier.com/overcladding-for-old-masonry-facades-why-it-is-important-to-think-performance-first/

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