Low-carbon construction means long-lasting construction. Resiliency, durability and recyclability are the hot buzzwords in sustainable building circles. When calculating the embodied carbon balance sheet for a project, there is probably nothing that goes straight to the bottom line like extending the life of the building does. Avoiding having to tear out major components and engage in long labour- and energy-intensive retrofits will be a coming priority for designers – especially on institutional builds but also on commercial construction if codes continue their present trend. So the pressure is on for facade designers to consider not only how their envelope will meet today’s needs, but also what will happen to it as its components approach the end of their lives. 

Building with more expensive, longer-lasting materials is an obvious answer and part of the equation. But there’s another wrinkle to consider. We know from recent experience that what is considered acceptable and even state-of-the-art today may not be tomorrow. Once upon a time the greatest environmental concern on a jobsite was smog-creating nitrous oxide emissions. Then deforestation entered the chat, encouraging limiting the use of lumber. General production of landfill waste rose up, touching off three decades of obsession with recycling. Next, toxicity from materials such as formaldehyde and asbestos had its day. Then came the big daddy: carbon dioxide. Mitigating that initially took the form of improving air/water tightness. Then thermal performance, which is morphing into solar heat gain as air conditioning becomes a bigger part of the energy budget in Canada. Now we’re moving on to embodied carbon. And don’t forget reflectivity and bird-friendly needs. 

All of this is to support the point that chances are some part of a facade built today (and most likely including the glass) are going to need to be replaced before the building gets torn down. Knowing this, it may be time to think about how glazing can be made easier to remove, replace and upgrade after installation. Moving designs in this direction would also address a long-standing request from property owners that designs be easier to service and maintain, even if their desire to pay for such features has been, uh, “limited.” We may be at a point in history where regulations drive interest in replaceable facades past the cost concerns.

The problem

Most glazed facades today are simply not designed to be taken apart at all, ever. The use of silicone to avoid mullions and caps and create unbroken glazed surfaces for esthetics is a major culprit. Cutting out silicone is “messy and labour-intensive,” according to Peter Dushenski of GlasCurtain, a stick-built fibreglass curtainwall fabricator.

Experts Michael Aoki-Kramer, Graham Finch, Brian Hubbs, Ed Thiessen and James Higgins from RDH Building Science outlined the problems with removing silicone-glazed facades in their 2015 paper, Re-Glazing of All Glass Curtain Wall Buildings. In it, they described replacing the insulating glass on a 48-story tower in Vancouver. “The building uses a unique aluminum-frame curtainwall system where the IGUs are adhered to the frame using structural silicone on the offset edge of the exterior-most lite. The SSG curtainwall achieves an architecturally appealing look with no extruding mullions or snap caps. The original IGU installation work was completed at the factory and the curtainwall frame was then installed on the building. This SSG system presented a difficult challenge with respect to glazing replacement work. The curtainwall frame could not be removed from the building, so the replacement work had to be completed in the field. […] In addition, the design of the curtainwall frame only allowed glazing replacement work from the exterior of the building. This meant the replacement work had to consist of:

1. Removing the IGUs from the curtainwall frame and discarding them;
2. Installing replacement IGUs in the curtainwall frame using structural silicone sealant;
3. Holding the replacement IGUs securely in place while the structural silicone cured;
4. Installing silicone sealant in the joints between the IGUs for water shedding and esthetics.”

RDH came up with a number of innovative solutions to these problems, which was why this paper was being presented at a BEST conference. These included a custom-built scaffolding ring to provide a work platform to lift the units to the required level and proprietary “clip rails” to hold the new IGUs in place while the silicone cured. The refurbishing project cost $6 million.

George Torok of Stantec has seen his share of hard-to-refurbish projects. “I’ve just been through some emergency repairs on a condo here in town with a leaky window wall in two locations,” he reports. “In both cases the culprit was poor cut-and-paste work with sheet stick-and-peel membranes. One location required disassembly of window wall components, which wasn’t too difficult but still awkward because some spandrel components were installed originally from the exterior and so could be removed. A few were not and required some creativity. The second location required disassembly of a ‘cassette-style’ metal composite cladding assembly that was installed shingle-fashion from right to left on each floor and from the bottom to the top of the building. It was theoretically demountable…as long as you were willing to strip from the top down. And the location we had to address was, of course, at the very bottom. 24 floors. Room for improvement in both designs, for sure.”

A common element afflicting most attempts to install replacement IGUs in existing curtainwall designs is the need to do so from the exterior of the building. This requires swing stage work handling heavy units then some method for holding the replacement units in place while the silicone cures. In the case of the RDH project, this went so far as to demand the design and manufacture of new clamping tools. Not something a building owner or renovation contractor wants to take on every day. 

Replacement of large units, even when it can be done from the inside, encounters an almost comical problem: they are sometimes too large to fit into elevators and staircases to be taken up to the installation floor. RDH had to modify the building elevators to take its new units up in the BEST case study.

Possible solutions

One way to start toward making facades more easily replaceable is simply to use stick-built systems. Because they rely on less silicone and more mechanical connections, they are always easier to take apart. But Dushenski notes that even SSG designs can incorporate more mechanical fastenings to make disassembly easier. “You can add a mechanical connection to it, like with toggles,” he explains. “Toggles will twist into the rebate between two of the lites. If there are three lites, it will be the inner two.”

Jeff Makimoto, technical advisor for Fenestration Canada, shared his thoughts on a system concept that would make replacing and upgrading curtainwall much more feasible. He thinks it could be possible to redesign both stick and unitized systems to make it possible to glaze them from inside the building.

1. Design a new integral cap and pressure plate as one hollow die;
2. Put the standard glazing gasket (normally on the mullion in the raceway) on the new cap; 
3. Design a pressure plate that goes around the full perimeter of the IGU;
4. Redesign the back mullion to accept a press-in wedge gasket around the full perimeter;
5. Size the glass and panels so they are taller vertically and installed with a lift and set method;
6. Size the glass and panels so they are smaller than the horizontal daylight opening by a minimum of 0.125 inch.

Makimoto thinks this concept would minimize or eliminate the need for external glass and panel replacements using swing stages and lift equipment (provided the units are sized small enough to travel in the elevator). He points out that replacement would then be much safer for workers and not require them to have large equipment tickets.

In general, older and more conservative facade designs lend themselves more easily to replacement. Punched windows can often be simply popped out and reglazed or replaced on site. Square and rectangular units on flat walls are much easier to remove and reinstall than odd shapes on articulated facades. Lower buildings overall make replacement from the outside more feasible. 

The future

Overall, the idea of making facades more replaceable and upgradeable runs up against a familiar opponent: upfront cost, and what project owners are willing to pay. “I’m not going to hold my breath,” Dushenski says. “The carbon conversations are still mostly in the sphere of larger owner-occupied institutions. Basically universities and different levels of government. They are looking long term and they’ll say ‘If we invest in a little better of a system now our energy costs will be lower and every single year our service costs will be lower for 10, 20, 30, 50, 100 years. And sometimes they will rationalize it in terms of carbon or other environmental things. But the developers will always build the cheapest things possible to satisfy their markets and their investors and their clients.”

Last word goes to Steve Gusterson of Alumicor. “Most curtainwall systems are aluminum framed and incorporate silicone gaskets. They last a very long time. The most common dramatic failures are either leakage – which is usually immediate and can be attributed to poor custom component design or general execution – or IGU failure. If the IGU lasts 30 years, chances are the framing, gasketing, air/vapour barrier and thermal break technology has advanced enough that the existing framing system would probably be unsuitable. To me, that means everything should come off the wall and an entire new facade installed. That offers the building owner an opportunity for a fresh look and the ability to upgrade to more current building envelope technology (for instance, getting rid of spandrel areas) and architectural design, leading to increased revenue. If the owner is upgrading the facade, chances are they are thinking a comprehensive upgrade to many other components as well. Roof, mechanical, interiors. So the most important element is that freaking IGU. It’s gotta last 50 years at least. Maybe VIG will become more affordable if the manufacturer can promise an extended life expectancy.”

Thanks a lot, Steve •