Recladding for renewal

Photo courtesy WZMH Architects.

A few decades after its construction, a tall office building begins to lose its lustre. Its exterior may look a little behind the times, which can negatively affect tenant retention. Capital repair also becomes a pressing concern when certain components of the building envelope are approaching end of life.

Recladding is key to renewing such buildings. Experience has borne out that close collaboration between architects and engineers is essential to the success of these projects.

A shift in motivation

Recladding modernizes and upgrades the building envelope either through the tactical replacement of one or more components, such as glazing or spandrels, or by replacing entire façades. This can address capital repair issues, improve tenant comfort and update a tower’s appearance—but in recent years, there has been a major shift in clients’ motivation for undertaking such projects. In an era of net-zero targets, decarbonization and environmental, social and governance (ESG) issues, recladding can help them reach their sustainability goals.

Collaboration between architects and engineers is essential to success.

Instead of demolishing an aging office tower and replacing it with new construction, recladding can revitalize a building while retaining the structural materials that constitute the bulk of its embodied carbon footprint.

“When you’re replacing a component that’s at the end of its service life, whatever you put in there is likely to be there for the next 50 years,” says David De Rose, managing principal at Toronto-based consulting engineering firm Synergy Partners. “So, make sure it’s tied to an overall decarbonization plan for the entire building.”

On any recladding project, the first steps are to gain an understanding of the client’s objectives and thoroughly examine existing building envelope conditions. Engineers’ detailed building investigations, which involve destructive testing and verification of as-built conditions, are a prerequisite in ensuring new design solutions can be included or excluded with confidence.

If the recladding is part of a comprehensive retrofit with a net-zero target, then the consulting engineering team and owner will develop an emissions reduction plan to be progressively implemented over time. Which cladding system components are approaching their end of useful life and which could be retained for longer-term use? The answers will help determine the best approach to the project.

In one recent recladding by WZMH Architects, building science engineers used in situ smoke tests to identify where air and water leakage was occurring. They proposed a detail to establish air barrier continuity and improve wall assembly resistance to water penetration.

Exp helped WZMH renovate 95 Wellington Street West to improve insulation, airtightness and water resistance in the roof and envelope. Photo courtesy WZMH Architects.

Choosing a method

There are many approaches to recladding, ranging in cost and complexity, that can be used alone or in combination on the same project.

At the lower-cost end of the scale, windows can be replaced with new insulated glazing units (IGUs). ‘Non-window’ exterior wall surfaces can also be renewed. Removing spandrel cladding panels allows access to fasteners that may need repairs and provides an opportunity to replace insulation and air water barrier (AWB) systems in the wall cavity to improve thermal performance, before installing new spandrel cladding panels. The existing spandrel cladding panels can either be repaired and reinstalled or discarded and replaced with new. As all of these cases involve retaining and reusing the back section of the existing mullions, the proportion of glass to solid wall remains unchanged.

Another option is to retain a portion of the existing mullions while attaching new cassettes, i.e. panelized units integrating new glazing and spandrels. This approach can streamline construction and makes it possible to alter the window-to-wall ratio, if desired.

When existing masonry wall assemblies are too onerous to remove, overcladding offers a solution. The masonry is retained and may be repaired, with a new envelope installed outside the existing one.

The aforementioned options are all suitable for buildings that will remain occupied during construction, as the bulk of the renovations are undertaken from the exterior by workers on height-adjustable ‘mast climber’ platforms, while any work that does need to be done inside can be scheduled outside of business hours.

“Make sure it’s tied to an overall decarbonization plan for the entire building.” – David De Rose, Synergy Partners

It is not always feasible, however, to retain and reuse a building envelope’s components. With a technical understanding of how recladdings are constructed, architects and engineers propose design solutions that can be implemented practically on-site. In some cases, this will mean ‘reskinning’ a building with a complete curtain wall replacement.

Looking ahead, new technological developments that are becoming increasingly relevant for recladding projects include building-integrated solar photovoltaic systems and vacuum insulating glazing (VIG).

Case studies

One example of a building that needed recladding is 95 Wellington Street West in downtown Toronto. This 23-storey tower, measuring 330,000 sf, is part of the TD Centre office complex, owned and managed by Cadillac Fairview (CF).

Decades after its completion, the stone façade’s fasteners were corroding, due to overtightening during their installation. Air and water leakage became problematic.

Building science engineers at Exp helped WZMH Architects lead a renovation project that combined insulation, airtightness and water-resistance improvements in the roof and envelope, replacing the reddish-pink granite on the exterior with new Bethel White granite. A new, self-adhered membrane installed in the cavity reduced water infiltration and increased airtightness to significantly enhance energy performance, while the upgraded insulation improved the building’s thermal performance.

The reskinning of Bell Canada’s tower at 76 Adelaide Street West incorporated double-glazed vision and spandrel glass. Photo courtesy WZMH Architects.

“With the recladding completed, all tenants are much happier with their workplace,” says Carlo Guido, CF’s senior director of project management and development.

Another example is a building owned by Bell Canada since its completion in 1965. Also located in downtown Toronto, at 76 Adelaide Street West, is a 16-storey, 432,000-sf tower with above-average ceiling heights.

By 2020, more than 50 years’ exposure to the elements had caused several components in the main façade’s integrated cladding system to deteriorate severely. Based on the findings of a destructive investigation, Bell opted for a complete reskin.

Prior to the removal of the building’s existing skin, a temporary wall was constructed in behind it, both to protect the interior and to create a zone for construction activities.

“On this project, we had an open canvas,” says Harrison Chan, principal at WZMH, which consulted on the project.

Approaches to recladding range in cost and complexity.

The team specified large-format glass panels with concave curvature on their exterior surface. Integrating double-glazed vision and spandrel glass, the panels spanned floor to floor. The slab edge detail included curved anchors and fire stopping to resolve the geometry between new and existing elements.

The project illustrated how recladding system types can be combined to address different conditions in different parts of a building, as a non-insulated overcladding has been completed on its mechanical penthouse. In the future, new insulation and cladding installed overtop the blank side walls could further improve building performance.

Today, WZMH is part of a multidisciplinary team conducting a study commissioned by Desjardins for recladding and decarbonizing an office tower at 95 St. Clair Avenue West in Toronto. As it happens, the architecture firm will be directly affected by the study’s outcome—since its head office is in the building.

Jennifer Davis is a licensed architect and the strategic business development lead for WZMH Architects, which recently launched Remake It Better: The WZMH Recladding Guide. For more information, visit www.wzmh.com/news/recladding.

This article originally appeared in the May/June 2024 issue of Canadian Consulting Engineer.