Glazing Retrofits Represent an Opportunity to Improve Performance and Comfort
by Jordan Scott
Performance, cost, sustainability and speed: these are some of the main drivers of commercial window retrofit in the U.S. If an owner wants better performance from their building’s windows or façade, replacement will cost less and be completed faster than demolishing the structure and starting over with new construction — plus the environmental impact will be lower.
Benefits of commercial window retrofit include maintaining historical integrity, reducing energy costs, improving energy performance and increasing occupant comfort.
“There’s a lot of good building stock out there and I think it’s a benefit to keep that and try to upgrade it rather than tearing it down, sending everything to the landfill and building something new,” says Anthony Cinnamon, associate principal at Wiss, Janney, Elstner Associates Inc., headquartered in Northbrook, Illinois. “In the next few years, the focus is going to be on how we can do more with the existing building stock when possible.”
“The most sustainable building is the one that’s already built; by retrofitting an existing building you are avoiding the additional carbon coming from manufacturing/construction of the structural elements,” adds Kayla Natividad, architectural technical services engineering for NSG Pilkington based in Toledo, Ohio. “The additional embodied carbon of new façade materials being installed are costs that in turn could provide significant savings to operational energy performance.”
While commercial window retrofit projects have unique technical, strategic and logistical challenges, understanding these challenges and how to overcome them can help minimize project obstacles and ensure success.
Current State of Retrofit
Due to the pattern of settlement in the U.S., East Coast cities such as Boston or New York have an older average building age than West Coast cities such as Los Angeles or Seattle. Because of this difference, many of the buildings erected before 1980 are still single-glazed, according to Stephen Selkowitz, FTI board member, Lawrence Berkeley National Lab (LBNL) affiliate and former group leader for LBNL’s windows and envelope materials group.
“Those are the buildings that are going to have the biggest challenges in terms of energy performance and, more importantly, in terms of comfort,” he says, explaining that in addition to poor thermal performance created by single glazing, metal frames, worn weather stripping and seals, the windows also likely have poor acoustical performance. “In many urban environments, better acoustical properties provide another market amenity.”
Certain types of buildings stand out as being good candidates for commercial windows retrofit. “From an aesthetic standpoint it’s buildings with historical significance or iconic façades; buildings that you do not want to or potentially are restricted from changing the appearance of but would like to see improvements in energy use and occupant comfort,” Natividad explains. “Realistically it’s something with good bones. If the structural integrity of the building is in good health, it can compensate for the addition of new and better insulating materials, and its design can meet occupants’ needs, it may be a good candidate. The façade elements can also impact if it’s a good candidate for window retrofits. If every other part of the building’s exterior is leaky and uninsulated, you can put in the highest performing windows and still have a leaky, uninsulated building. Heat transfer takes the path of least resistance.”
Cinnamon has seen a trend in Chicago where owners target highrise residential buildings from the 1950s and 1960s with non-thermally broken, single-pane glazing for window replacement.
“A lot of building owners have been trying to put a Band Aid on their windows, but they’ve finally gotten to the point where they realize that it’s an occupant comfort issue as well as a dollar and cents issue. They can save money on their heating and cooling bills by replacing those windows,” he says, adding that if the building’s HVAC system is being replaced but the windows are inefficient, then they won’t be getting the most out of that investment.
In large cities like New York, general retrofitting of apartment buildings for energy efficiency improvements and maintenance reduction remains the focus. However, adaptive reuse is also popular. Cinnamon has seen a turn-of-the-century office building become a hotel, and warehouses have been converted into offices. This trend is happening across the U.S.
“Most retrofit projects nationwide are adaptive re-use applications, such as converting warehousing and factory structures into living space. Many of these are driven by federal and state historic tax credits,” says Josh Wignall, chief marketing officer at Quaker Windows & Doors in Freeburg, Missouri.
“With the benefit of tax credits aside, building owners are seeking to improve the overall energy efficiency of their buildings to reduce the HVAC load and decrease utility costs,” adds Gary Shinault, national architectural consultant at Quaker. “Another driver is the elimination of maintenance. An older wood or steel window will require paint re-application every five to seven years to stave off water damage, which rots wood and rusts steel. Since deterioration of these is so common, the building owner may have no choice but to replace them.”
Sustainability is integral to commercial window replacement. Wignall points out that while modern building design emphasizes energy efficiency, retrofitting an older building with new windows can close the gap to today’s performance standards without sending the rest of a building’s materials to the landfill.
“Since most of the heat gain and loss occurs through the fenestration units in a typical older building, replacing those with new products designed for higher energy efficiency will most likely improve an older building’s overall thermal performance,” he says. “Also, there are both federal and state historic tax credits available to building owners and developers, which, when combined, can offer as much as a 60% credit for the entire renovation cost of a building if the building qualifies. Though the window replacement design must meet specific guidelines to maintain the historic character of a building, generally, the windows are allowed to be replaced with a product that will improve the overall thermal performance.”
High-performance replacement windows that meet these guidelines while contributing to maintaining a building’s historic character are becoming more available.
“It creates a win-win scenario,” says Wignall.
Project Strategy
Commercial window retrofit projects aren’t always easy. There are many variables to consider. As Natividad explains: “Existing profile and weight tolerance are two significant factors. If you replace with something of a similar profile and thickness it is more straightforward and can minimize on site labor. If you are adding additional weight you may have to take some extra work to ensure structural compatibility. If the building is currently occupied then disruption due to construction may be a concern. In these cases, we see secondary window systems being more widely adopted. And now as discussion around glass recycling and deconstruction over demolition gains traction, design teams are starting to consider what to do with the units that are being replaced.”
With so many considerations to keep in mind, Selkowitz recommends project stakeholders start by clarifying and quantifying their performance goals where possible, such as meeting or exceeding current code requirements, improving energy performance, minimizing life-cycle carbon and ensuring that occupant visual and thermal comfort is ensured for the next decade or two.
“What do you want to do in terms of occupant comfort? Design and optimize for that because you only have one chance to do it,” he says. “Lighting systems tend to get upgraded every 10-15 years or so, and HVAC is often replaced every 20-30 years, but the building envelope can be in place for 50-plus years. So, if you’re going to make a change, you want to do as much as you can within physical and cost limits, because you probably won’t have a chance to come back and replace it any time soon.”
The building will likely also need to undergo an engineering analysis to assess the façade’s structural integrity and ensure that a replacement curtainwall or window has something solid to attach to. If the building has long-term water damage that resulted in corrosion of the metal structure, then that needs to be considered and addressed.
“Depending upon your findings, that would influence where on the design and performance spectrum you could go with your window replacement,” says Selkowitz.
Rather than entering a commercial window retrofit project with a product already in mind, Wignall encourages stakeholders to contact a qualified window manufacturer for detailing and specification writing assistance.
“A qualified window manufacturer will have a network of sales representatives and contractors who will perform a site evaluation to determine the most efficient installation method and identify specific components and accessories needed for a successful installation,” he adds. “Having these components identified on the project documents will ensure the project will be completed without additional cost and adequately designed. A qualified window manufacturer will have the capability to accept an architect’s drawing file and offer adjustments.”
Product Selection
Choosing the right product for a commercial window retrofit project can be challenging. Historic preservation requirements, performance requirements and limitations created by the size of the openings or the building’s structural frame, all must be considered. The types of windows being installed are dependent on what is installed already, points out Natividad.
“Some buildings may want to keep their existing look and maintain that thin profile sash. In cases where a monolithic glass lite is being replaced they may be looking at vacuum insulating glass (VIG) for replacement; especially if they are maintaining their existing sash,” she says. “In cases that have uncoated or early insulating glass units (IGUs) where they can already support the weight and profile of a dual pane unit, they may just be upgrading to modern IGU performance (low-E #2, argon fill). If they are looking for higher performance you may be seeing the adoption of a 4th surface low-E, thin triple or hybrid IGU that can fit in the existing cavity.”
Shinault explains that some characteristics of historic windows can be challenging to replicate.
“In most cases, these involve original steel window frames with very narrow profiles… Many old industrial buildings depended on a maximum amount of visible light for worker visibility, so it’s common to find giant window openings in these buildings with steel frames and very narrow frame and muntin profiles,” he says. “The federal and state reviewing authorities tend to relax some of the narrow perimeter replication requirements due to the impossibility of matching with a structurally and thermally adequate new product, but there is a major challenge presented when the openings are too large for a single window frame.”
Shinault adds that combining two or more frames into one opening produces a very wide rail profile where they butt together. This can lead to push back from the reviewing authorities since the original steel windows usually do not contain wide breaks in the consistency of the window opening.
“Also, stringent energy efficiency requirements in areas like Massachusetts sometimes require triple glazing in windows to reach the thermal performance goals, but triple glazing is not widely available in historically-correct products,” he says. “Quaker has focused on developing historically correct products where the frame outperforms the insulating glass unit with a new barrier system that does not require triple glazing in many cases, where other traditionally designed products will.”
Shinault explains that, when choosing replacement retrofit windows, it’s important to ensure that they are designed and independently tested to withstand the building’s design pressure and water and air infiltration resistance expectations.
Many project stakeholders might overlook the effect of supplier stock on price and lead times, according to Selkowitz. For example, triple glazing is the default code standard in northern Europe, and specification for double glazing may cost more than triple because “special order” products almost always add more cost.
He recommends not considering design solutions solely based on components. Instead, it’s important to consider the supply chain, standard practice vs. special order and supplier/contractor coordination for the products and solutions they provide.
Working with innovative owners and architects, and groups such as the Department of Energy or state energy agency offices and utilities can bring experience in this space as well as proven examples of how these products work, what they actually cost and where to get them.
Alternate Solutions
Today’s market has a variety of modern, highly insulating glass and glazing products, from thin triple and VIG, all utilizing advanced low-E coatings. Selkowitz says installing these high-insulating glazing products might allow you to reduce or even eliminate the need for a perimeter heating system with vents next to the windows that keep occupants comfortable. HVAC cost savings can offset some of the façade retrofit costs. And if the envelope retrofit includes replacing the gas heating system with an electric heat pump, the downsized thermal load may make the new, smaller HVAC system more affordable. Achieving such savings relies on the architect and engineering teams understanding this trade-off and being able to model, optimize it and sell the overall package to the owner.
If the owner has only operated buildings in cold climates with perimeter heating systems, they may see it as too big a risk. But if the project team can point to other use cases where this strategy has been implemented and works, Selkowitz says, that’s a great advantage.
“We’re in an industry where no one wants to be the first to deploy a new product or system. They may want to be first from a design point of view, but they want to let someone else take the technical risks,” he says.
Selkowitz says there is a range of other retrofit solutions available, depending upon existing conditions and the retrofit performance goals. If occupant complaints focus on overheating due to the solar gain, for example, there are automated shading devices and secondary glazing with enhanced solar control. These can be especially useful solutions when occupants are leasing the space and capital improvements will be minimal.
Site Logistics
Occupancy is one of the main factors that impacts site logistics. If the building has residents actively living there or offices being leased, replacing the windows or façade becomes more challenging.
Whether or not the building is occupied also impacts sequencing, and how likely the window replacement will be done from the interior or the exterior. Cinnamon explains that contractors need to have a plan on how to protect the interior and any furniture in the space when replacing windows in an occupied building. Occupants will have questions about when it will occur, how long it will take and who will move the furniture. In the shortest cases, it can take two to three days. Sometimes, residents find alternative places to stay and work during that period.
“It hits them where they live. Sometimes that can be a tough sell,” says Cinnamon. He recommends that project stakeholders hire a project manager to manage site logistics and communicate important information with building occupants.
The building’s location also affects site logistics significantly. If a building is in a dense urban environment, the contractor teams have more limitations related to site access than projects in less dense areas with more space and easy access to the building façade.
In an urban context, contractors must consider whether there is space for staging window materials, cranes and other installation equipment. Selkowitz says in these situations, replacing or updating the glazing from inside the building, such as with secondary glazing, is easier than having to access the exterior façade.
The site logistics plan should also include removing the existing windows. It is helpful to know the specifics of the building’s freight elevator early on.
“During demolition and removal of existing window sashes and frames, friable hazardous materials, such as lead or asbestos, may be present. Those can be removed successfully, safely and easily by an abatement contractor. Many window replacement contractors are certified to perform this work,” Wignall points out.
Each area of the United States has unique climate concerns, which, along with local political and economic factors, can impact the codes it adopts. For example, Boston is in a cold climate and has adopted stringent stretch energy codes. Triple glazing could be necessary to meet the 0.25 U-factor requirement. Cinnamon says that, due to costs, few people would specify triple glazing just to have it. Codes are driving the adoption of triple glazing in the U.S.
Code Requirements
According to Wignall, retrofitted windows are generally expected to meet the same code requirements as windows in a newly constructed building. However, this depends on the amount of glass being replaced.
“Associated challenges are, in most cases, related to ADA-compliance, energy efficiency standards and egress. Those can all be successfully addressed by an adequate replacement window product, as doing so will also bring many older buildings up to the current standards,” says Wignall.
“Projects with historic tax credits are required to follow the Department of the Interior standards, meeting the required high visible light transmittance, making it difficult for some manufacturers to meet more aggressive energy efficiency requirements. With that said, currently, products that meet both standards are available.”
If no federal or state historic tax credits are available, the project stakeholders must still investigate whether there are any city or neighborhood requirements or reviewing entities that may require certain profiles of the original windows to be replicated or left in place, according to Wignall.
“Those can vary extensively. If there are historic tax credits available, there are specific guidelines from the Department of the Interior through the National Park Service which must be followed for replicated profiles of the original windows,” he explains. “This involves a submittal process in which a window manufacturer with experience in this market can assist, working hand in hand with the architect or a historic tax credit consultant.”
Change Needed
Window or façade replacement is usually more sustainable and cost-effective than building new. That’s especially true today with tariffs complicating the commercial building market. Many building owners may be tempted, however, to leave a building as is, no matter how inefficient the window performance.
“Energy performance isn’t necessarily something people can taste, touch or look at. It makes it difficult to convince people that [upgrading their windows] is in their best interest,” says Cinnamon. “If they’re having a problem with water or air infiltration or, in an extreme case, structural problems with the windows, it’s a lot easier to convince a building owner that it’s time to replace their windows.”
He adds that, from a strictly energy standpoint, many building owners think, “Yeah, so what? I’m used to it and I don’t want to spend the money to do it.” However, when owners have chosen to replace their windows or facades, they say they’re glad they did it.
That’s why Wignall believes that more robust historic tax credit programs should be available from states that offer either no tax credits or minor credits.
“More tax credit opportunities will create a more favorable environment nationwide. Historic tax credits have been found to be successful in states that offer these robust programs by creating economic development in otherwise blighted areas, thus generating revenue,” he explains. “Also, it has been found that a typical restoration project will produce much less carbon footprint than a new construction project from the ground up.”
In addition to expanded incentives, Cinnamon says improving the recyclability of glazing units and the efficiency of the recycling process could increase the frequency of window replacement. Recycling window units is difficult because of their components, such as aluminum framing, glass, lamination, gaskets, sealants, etc.
“All those things have to be stripped down and cleaned before you can separate them and get them recycled,” Cinnamon explains. “We hear from window contractors that it’s actually going to cost more to recycle the units than the money that could be paid back from recycling.”
Improving this process could have a positive impact on the industry both from a cost and environmental standpoint. Cinnamon adds that many building owners would feel better about retrofitting if they knew that all the old material wasn’t going to the landfill and that they might get a few dollars back.
Selkowitz hopes to see the industry embrace secondary glazing more, due to its excellent energy performance, lower cost and quicker, less disruptive implementation compared to removing and replacing existing window units.
“I think it’s one of the more exciting options because it gives you very high performance levels, especially when adding double-glazed secondary units,” he says. “…Films and full replacement options have been around for a long time and serve some key market needs, but the secondary glazing piece is most interesting as it provides some new, technical and business/cost options.”
Natividad says one major change that could help drive growth in the retrofit market is the general acknowledgment that high performance products are available and not necessarily new technology.
“Especially when dealing with punched windows, there are a number of fabricators and window manufacturers that have the ability to make a thin triple today. VIGs have been commercially available for over 25 years. Room-side low-E’s even longer,” she says.
The difficult thing about glass performance progression over the last 45 years is that it is not very visible to people that do not look further than what the unit looks like, Natividad adds.
“It’s two pieces of glass with a spacer separating them. All of the widely adopted innovations in that time improving glass performance aren’t apparent to those outside of the industry: the adoption of low-E coatings (with continuous improvements in performance), optimization of gas fills, spacer technology improving edge effects, thermal breaks and general design of framing systems,” she explains. “From the outside it’s still two pieces of glass in a frame. It’s hard to sell a benefit that is not outwardly visible. I’m hopeful the next step changes being discussed and adopted today that are more visible (VIG, multipane IGs and the use of thin glass) will drive more adoption of high-performance glass options.”
It’s also worth noting that many all-glass skyscrapers were built in the 1960s-1970s.
“A building has to be at least 50 years old to be considered historic in the U.S. so while up to this point a lot of our historic restoration industry has seemed to be lower window-to-wall ratio and punched windows, we may begin to see more all glass façade retrofits that need to meet historic requirements,” says Natividad.
While Selkowitz believes that more needs to be done, he is excited to see that the industry is taking positive steps.
“There are existing and emerging product options now that will allow you to improve the existing building stock faster, better and cheaper. That’s a great opportunity,” he says. “We’re still on a nationwide learning curve to best match the new product options with market needs. Some of that is climate dependent, and some depends on building type, but there’s a lot of learning. Hopefully, those learnings will be translated into more and better products at lower cost and that more experience will build confidence in these options that will further reduce some of the risks and rapidly grow market impacts.”
What about Life Cycle Assessments?
Life Cycle Assessments (LCA) are becoming more and more common on today’s façade projects. According to the Department of Energy, an LCA is a comprehensive method for assessing a range of environmental impacts across the full life cycle of a product system, from materials acquisition to manufacturing, use and final disposition.
Having an LCA can show architects and owners how high-performance glazing solutions, whether in new construction or a retrofit, pay back the initial environmental cost through long-term energy savings.
Jordan Scott is a contributing writer for USGlass magazine.
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