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Net-Zero Renos

September 30, 2021  By Andrew Snook

Updating older buildings to meet today’s standards can pose a number of unique issues including incompatibility of materials and added strain on the existing façade. Photo credit: © Shanshan533 |

Countries around the world are constantly looking for new ways to reduce their carbon footprints to decrease the speed of global warming.  As part of this global effort, Canada and 120 other countries have committed to reaching the goal of net-zero carbon emissions by 2050. One of the keys to successfully meeting these targets will be reducing the carbon emissions produced by existing and new buildings.

This means national goals and standards for building energy efficiency will only continue to increase. 

“I do think it poses new challenges, but it also poses new opportunities. The industry is constantly changing and we’re constantly improving and trying to get better,” says David Heska, director for southwestern Ontario building sciences at WSP Global. “Yes, this is a bigger step forward, but it’s not like we haven’t seen change in the past.”

Heska says façade designers and glazing installers have had to re-vamp and adjust as standards and building energy targets have changed over the years, and they can do it again.


From a new building design perspective, Heska says the new energy efficiency goals will stress more consideration being placed on looking at every aspect of the building envelope as being connected.  

“The building envelope and mechanical system is connected,” he says. “It is much more common now to have the building envelope renewed at the same time you’re considering what type of heating and boilers and HVAC systems you need inside your building. If you’re going to do both, do them together. Don’t think you’re just going to tackle the building façade and not touch the mechanical systems at all because if you make your façade way tighter you increase the R-value from R2 or R3, which is most glass buildings, to R5 or even up to R10, then the amount of heating and cooling you need changes drastically. You have to consider them both in line.”

For glazing contractors, Heska believes the new goals will mean a shift in focus on air tightness. 

“All of the details – where the connections of the roof ties into the top of the walls, where the penetrations occur, where there are thermal breaks at balcony slabs or other locations, the amount of air barrier detailing – a spotlight is going to be shined on that in the next five to 10 years,” he says. “This will result in glazers not just having to be glass installers but also thinking about the air and vapour barrier. All of their caulking and sealant detailing is critical to installing this curtainwall or window wall glass system.”

Ted Redlarski, owner of Noram, says the technologies are available to counter any challenges related to meeting energy targets for existing and new buildings. The question is whether a building owner is willing to pay for those solutions.

“No question the technology is there, but it’s expensive. Therefore, few clients are willing to buy. Some lose money on it because the benefits aren’t compensating the costs fast enough,” he says. “As technology gets invested into further, it will get cheaper. Right now, most of the novelties are expensive for the average investor in any market. The rich companies or governments that spend on PR are going to those novelties, but there’s not a high enough return for the average investor.”

Existing buildings
Will there be significant differences in older building structures that make it harder to integrate today’s windows and curtainwall? Well, it depends.

“Some buildings are easier to integrate than others,” Heska says. “Some buildings we are able to reuse and salvage some of the framing elements in place, if it was designed to be able to take larger structural loads. In other cases, we’ve installed a secondary outer skin – left the first façade and glazing system in place and just re-skinned over top of it and almost abandoned the one in the wall below.”

He says that re-skinning over the existing framing can prevent having to demolish an entire section of a building.

“It’s helped with some of the façade renewal because, if you don’t have to rip everything off, then you can just get rid of those glazing components and vision glass areas once you get there,” Heska says. “Contractors and building owners and occupants like it if it can be done in one day because it’s fast.”

George Torok, principal, façade specialist, at Morrison Hershfield, says the challenges with existing buildings will be wide-ranging depending on the kinds of buildings someone is looking at upgrading. 

“Are you considering replacing isolated elements? For instance, if you have an older building with individual punched windows. Or are you thinking about replacing and tearing off exterior skin and starting again? There’s a huge difference there, because if you’re replacing individual elements, then there’s only so far you can go,” he says. “There’s also a certain rationality there that, typically, windows are the weak point thermally in a building envelope. So, it doesn’t make a lot of sense to take a window to the point where it’s better than the rest of the surrounding building envelope. Then you’re just transferring problems from one element to another.”

Different sized openings
When it comes to different-sized window openings, Heska says staying up to date on codes and standards is vital.

“We design professionals need to be on our toes and staying up to the current best practices related to the various changes that are occurring to the Ontario Building Code and other guidance,” he says.

This is true for safety as well as energy efficiency.

“The industry building inspectors, as well as some architects, haven’t considered all of the factors they need to when designing large window openings,” Heska says. “Especially in higher levels of buildings because the wind loads that those glass elements and glazing elements need to take are higher. They also need to withstand any sort of impact load.”

Incompatible materials
While not a common issue, some glazers have experienced issues with their current adhesives being incompatible with some of the older adhesives.

One of Torok’s colleagues, many years ago, experienced this issue while working on a building that was built with structural silicone-glazed insulating glass units. Constructed in the 1970s, the early days of structural silicone glazing, the units had reached the end of their useful life and needed to be replaced. But when Torok’s colleague tried to replace them, he found the new adhesive wouldn’t bond with the original adhesive.

“The problem they found was in trying to find new structural silicone sealant that would adhere to the old sealant. Generally, you try to remove as much of the old sealant as you can, but you don’t want to damage the surface of the existing frame. So, there will always be some residue on the metal surface,” Torok explains. “They could not find a new silicone to bond to the old silicone, so they had to add very thin strips of metal on to the existing frame and mechanically bond that to the frame, which provided the new surface.”

Beyond that more sophisticated example, Torok says other issues with older sealants can occur.

“Older sealants, if they go back long enough, might be linseed-oil-putty-based,” he says. “It might be very difficult to remove them because they’re extremely hard and removing them could cause damage to the underlying material.” 

That said, there are pre-construction reviews that glazers need to go through for a structural silicone glazing project, and one of those is adhesion testing.

“You want to make sure the sealant will stick to the substrate. Adhesion quality can change depending on the finish material like the paint. You might need to use a primer with a particular sealant. A primer-sealant combination might not work, and then you might have to change,” Torok says.

Exceeding weight limits
Older structures can sometimes present a challenge with not being able to handle the weight of today’s façades.

“If you’re looking at really old systems that are single-glazed, and you’re simply adding another layer of glass in it, making it double-glazed, that’s an extra three pounds per square foot for a 6-millimeter-thick glass. So, it does add load,” Torok says. “If you need to have a more robust system of glazing, then the existing framing may no longer support it. Existing anchors may not be good enough, so you may have to tear the whole system out and re-engineer the anchors.”

Heska says he has not worked on any catastrophic failures related to structures not handling the weight of today’s façades, but he has heard of projects failing.

“There is a project I’m aware of where the façade loading was too large and, as a result, some of the existing structure began to crack,” he says. “Those are one-offs and not common. A designer cannot just assume that the original building can just take this new load. Calculations and analysis need to be undertaken to determine if the new façade works.”

Although it is possible for an older structure to encounter weight restrictions, Redlarski says it’s unlikely to occur.

“This is applied engineering that can always be solved with different costs, I don’t foresee a problem,” he says. “Typically, the new façades are lighter than the old ones, and the old structures, they would stand the test of time.”

Redlarski says that the real issue is justifying costs to building owners.

“Some owners still withhold going ahead for updating buildings to standards that are leading edge because they cannot increase rents to offset this.” he says.

Ventilation challenges
In the old days, people relied on opening their windows to get fresh air but, for decades, people have relied much more on mechanical systems. But with a desire to include more exterior ventilation to help meet future emissions targets, many challenges lie ahead.

“With the people thinking ahead to those aspirational goals – the 2030 and 2050 challenges – there is a desire to include exterior ventilation,” Torok says. “But how do you integrate that with the mechanical systems of a building? That’s a big question.” 

In existing residential buildings, one of the bigger issues is window-mounted air conditioners.

“I’ve been in buildings where people have taken hammers and hacksaws to aluminum windows to fit their air conditioners,” Torok says. “It makes far more sense to buy a new air conditioner that’s smaller that fits better into the opening. But, you own it already, and you have to go out and buy [the new unit]. So, you need an incentive to get rid of the old unit.”

Torok watched a presentation years ago by Toronto Community Housing where they were trying to solve the challenge of retrofitting their older buildings where residents were using a variety of older air conditioners causing the building’s energy costs to soar. To help solve this issue, residents were offered floor-based air conditioners that have a simple duct system that is placed into the window openings. This solution significantly reduced issues related to air leakage, water leakage and trouble accessing exterior walls for maintenance.

“It saved them operating costs. It was actually cheaper to give everyone a new air conditioner,” Torok says.

Insulation and thermal break challenges
The insulation of new façade systems has higher insulating values that the Toronto Green Standard (for example) is calling for, and that standard (and similar ones) is resulting in a greater focus on where the weakest points have been, which are the thermal breaks and transitions, Heska says.

“With all of those thermal breaks and insulation challenges, there are typical details and best practices that can be followed,” he says. “Designers now have the ability to determine, if you were to construct it using this certain drawing and details, then you’re going to achieve an R-value of five. Where, if you made this slight improvement, you can get an R-value of eight. We can do that when we’re designing, but we also need to have the installers in line and understand why these changes have been made. If we just design it, and it doesn’t get constructed that way, it’s kind of a waste of time.”

Heritage buildings
Heritage buildings can sometimes present additional challenges since there is typically a strong desire to maintain the original look of the building as much as possible.

“In can be difficult,” Torok says. “For instance, if you have an existing building with steel framed windows, steel can be very high strength. So it can be very narrow, and it provides potentially a very light appearance to the glazing. If you’re bound to keep that, it’s difficult to achieve that in any material other than steel. It is possible to get thermally broken steel-framed windows that look very similar to traditional, non-broken, steel-framed windows. But that’s expensive to deal with and the thermal performance is not that great. So, then it becomes a question of looking at other aspects. Are the frames still in good shape? Are there other elements surrounding the windows that might need repair that would justify a replacement?”

Heska says there are certain buildings that can’t be brought up to the current standards for air tightness and thermal insulation, because if glazers and designers were to do that, it would cause other issues to the heritage elements of the buildings. 

“There has to be some discussion between the owner of the building, the engineer-designer, and the local jurisdiction looking at imposing the efficiencies of buildings, because there’s a bit of trade-off between the two in some cases. Most of the people that I’ve talked to on the owner’s side, and the enforcement side with inspectors, understand they don’t want the nicest building in downtown Toronto that are heritage to all of a sudden have components falling off the outside face because they’ve insulated the inside too much.” •

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