Rejuvenating old masonry facades with overcladding

by arslan_ahmed | April 3, 2023 10:00 am

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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 centre 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 facades, foundations, and roof assemblies.

While some historic enclosures merit careful restoration, in other cases, non-heritage or non-culturally significant buildings simply need to be renovated and modernized for the long-term. Commercial, institutional, and government owners are increasingly turning to facade 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 neighbourhoods.

Many cities across North America 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, architects can design a new insulated facade layer and vapour barrier, making the enclosures watertight, energy efficient, and attractive. Examples include a 1907 school 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 esthetic exterior treatment. Similar to a reroof overlayment, adding new envelope construction over existing masonry, concrete, brick, and other facade materials presents an effective and desirable approach for revitalizing building facades in reconstruction projects.

[2]The approach offers the opportunity to incorporate new esthetic 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 Toronto and New York, 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 North American market in the early 1970s, provides an adaptable opportunity for overcladding, insulating, and waterproofing on older or poorly designed masonry facades—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 concrete masonry units (CMUs) or brick veneer.

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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 structure reinforcement and additional columns, beams, or an underpinning foundation.

According to the National Research Council Canada (NRC), the original rainscreen principle consists of “a cladding, made of a lightweight, low water-permeance and low water-capacity material, installed on the exterior of a solid load-bearing brick wall, with a drained and vented air space between the cladding and the load-bearing wall.”¹ This concept evolved to include the “open rainscreen wall” that addresses all forces which could lead to rainwater penetration.

The NRCC Division of Building Research 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 has proved to be 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. For instance, thermal performance and air tightness are significantly improved, which helps eliminate moisture and condensation issues. Further, 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 facade stabilization and insulating options.

Specific considerations for facade overcladding approaches are like those for any enclosure assemblies retrofit 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 in addition to short design and construction schedules.
• Allowing the building to be largely occupied and accessible during construction.
• Limiting the amount of 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 per cent of the dead load threshold for steel structural members, and 10 per cent of building lateral loads.

Done well, overcladding will improve building esthetics 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 vapour barriers transitioning into window openings, and the sealing of all window-wall interfaces.

So where does one start? For example, how much insulation is required, and where should the vapour barrier be located? What are the benefits and disadvantages of overcladding for masonry assemblies? These are 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 vapour barriers. The building configuration, orientation, and the local site’s topography, prevailing winds, external shadowing, and direct sunlight will determine what the enclosure needs during heating and cooling seasons. In all climates, ci 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 modelling (BIM) or U-value calculations to determine enclosure properties. Another option is the simplified building energy model (SBEM), a 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, uses, and location. For projects in Canada, the team should ensure compliance with the National Energy Code of Canada for Buildings (NECB), Part 8.

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Moisture

Water vapour 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, and 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 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 mould occurrence—the project specifiers and architects should have designers determine how much water vapour could be generated within the building and determine the resultant increase in internal vapour pressure above the external air. After making this determination, the performance expectations and physical properties of the enclosure assemblies can be assessed.

Overcladding for performance

These solutions are complicated and challenging to explain to stakeholders who are not building professionals. 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 frequent 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, facade overcladding, and targeted expansions represent cost-effective approaches to making the most of existing K-12 schools, 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 neighbourhood 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. 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 and funding to fix them is allocated.

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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 facade upgrades can be accompanied by the replacement of outdated, thermally inefficient windows. Today, as many older, masonry load-bearing walls are 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 appearance that inspires little confidence in the community the school serves. Instead, overcladding wraps the entire masonry facade 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 facade overcladding of a public school built in the late 19^th century. The aging brick facade of this remarkable school building had naturally begun to weaken after more than a hundred 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 recreated some of the original architectural components, matching them exactly to produce a cohesive look that honours the familiar and the 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 public-school example, the 1907 facility required a means for improving the energy performance of its enclosure, while returning distressed and discoloured 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 severe moisture damage to the academic spaces inside, as revealed by a site survey, to protect students and staff from mould 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.

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The building was determined to be an ideal candidate for facade overcladding. The existing wall could be treated with an exterior parge coat and moisture barrier, followed by a drainage mat. Finally, a new brick face would be installed in a colour 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 were installed over existing, rehabilitated steel. Durable windowsill upgrades included flashing and sub-sill pans, and the parapet, stripped of its original character over time, was rebuilt with concrete curb and hung with an ornamental cornice composed of glass fibre-reinforced concrete (GFRC).

Author’s note: In a future article, the author will discuss/explore ideal placement and attachment of insulation and air barrier within the assembly, critiques of EIFS overclad solutions, various structural considerations including potential thermal bridging and construction costs, appropriateness of face-sealed systems in certain climate regions, and questions about air barriers.

Notes

¹ Visit the National Research Council (NRC) Publications Archive to read “Evolution of wall design for controlling rain penetration.” doi.org/10.4224/40002861[8].

[9]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/rejuvenating-old-masonry-facades-with-overcladding/

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