In the quest for net-zero, doors and windows remain backup players.

By Drew Vass

Green Home Lingo

Zero Emissions: A home that generates and/or purchases enough renewable energy to offset emissions from the energy used over a year

Zero Energy: Generates as much renewable energy (from PV and other sources) as it consumes over a given year

Positive Energy: Generates more energy than is consumed over a year

Zero Energy Ready: Reduces energy to the point that any remaining energy needed can be offset with renewable sources

As demands for housing lap new home production by nearly four million units and the nation faces what President Joe Biden refers to as an “affordable housing crisis,” contractors, builders and materials suppliers now face other annual threats: fire and hurricane seasons. Meanwhile, according to decades’ worth of data gathered by the National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Environmental Information (NCEI), each new year poses the possibility for being the worst yet.

“Storms are getting bigger, more frequent and more intense,” says Marc LaFrance, windows technology manager on the Emerging Technologies team at the U.S. Department of Energy’s (DOE) Office of Energy Efficiency and Renewable Energy. “And this is something we all have to face as a society. We’re really at a key point here,” he adds.

Why is DOE’s windows expert weighing in on extreme weather? As a renewed focus on climate change pushes the envelope for net-zero homes and buildings, fenestration can be part of a solution, LaFrance suggests.

According to NCEI’s data, since 1980 the U.S. has sustained hundreds of weather and climate disasters when the overall costs for damages reached or exceeded $1 billion (including adjustments based on the Consumer Price Index). In order to avert the possibility for a total climate calamity, an Intergovernmental Panel on Climate Change (IPCC) says global warming must be limited to an increase of no more than 1.5 degrees Celsius by 2100. Reaching that goal requires steep reductions to greenhouse gas (GHG) emissions, IPCC officials say, including cutting global carbon dioxide
(CO2) emissions roughly in half by 2030 and to near zero by 2050. At the same time, “Buildings are responsible for 36% of carbon dioxide (CO2) emissions in the U.S. and will thus be integral to climate change mitigation,” say scientists at Lawrence Berkeley National Laboratory (LBNL). Within those discussions, however, no one seems to be cuing better doors and windows, LaFrance says. “We keep losing ground to the opaque envelope,” he suggests. Builders are increasing attic insulation and boosting walls to R-30 performance, “but yet we still have double-pane, low-E windows,” he says.

Stiff Competition

With the call for added efficiency among homes and buildings, numerous states are edging their way to net-zero energy use requirements—pointing to climate change as a primary driver. In Massachusetts, for instance, Governor Charles Baker is calling for “bold and urgent action on climate change,” linking his state’s efforts to the cost of natural disasters.

In a report entitled “Assessing the Potential to Reduce U.S. Building CO2 Emissions 80% by 2050,” LBNL scientists found that a “combination of aggressive efficiency measures, electrification, and high renewable energy penetration” could reduce emissions by 72%–78%, relative to 2005 levels. Many of the details outlined by those researchers (who know their fair share about fenestration) place windows on par with solid walls, in terms of importance, but mentions of higher performing windows are rare. Energy conservation measures applied to building envelopes “contribute somewhat smaller but consistent cost-effective emissions reductions across the full model time horizon—particularly air sealing and highly-insulating windows and walls,” the laboratory’s scientists say.

So far as why better windows haven’t found a prominent role in the discussion about net-zero performance, more advanced tools for achieving those goals not only exist, but, unlike high-performance windows, some have become more affordable, studies suggest. According to studies conducted by energy research and consultancy firm Wood Mackenzie, costs for solar photovoltaic (PV) systems in the U.S. are falling faster than anticipated across all market segments. Since 2009, prices for PV panels have dropped by 90%, experts at Energy Innovation Policy and Technology LLC report. Wind turbines have dropped by 71%, they say, and LED light bulbs by 80%.

In addition to falling costs for things like solar energy, officials for the International Code Council say today’s new homes don’t have far to go in order to reach net-zero—with the windows they have. From 2006 to 2021, code changes have increased efficiency requirements by about 40%, or an average of 8% per cycle, they say. At that rate, the base 2021 International Energy Conservation Code (IECC) efficiency requirements are just 10% away from net zero for residential buildings, officials add. But while the latest codes include “large increases for the opaque envelope,” LaFrance says, requirements for windows remain more or less static.

But One Way In

In the absence of stricter codes, among the only factors capable of adding fenestration to a national focus on energy includes tax credits and rebates, some experts say. But there are indications those measures are coming.

In recent months, President Joe Biden debuted the American Jobs Plan, calling for significant investments into rebuilding the U.S. economy. Amid what the President refers to as “the affordable housing crisis,” the plan calls on Congress to “help produce, preserve, and retrofit more than a million affordable, resilient, accessible, energy efficient, and electrified housing units,” through such things as targeted tax credits, formula funding, grants and project-based rental assistance. By passing the bipartisan Neighborhood Homes Investment Act (NHIA), Congress would grant $20 billion worth of tax credits to be disbursed over the next five years, resulting in approximately 500,000 homes being built or rehabilitated. In total, the President’s plan would invest $213 billion into construction and retrofitting. While a focus on energy retrofitting is wrapped in plans for infrastructure development and other initiatives, the idea for combining net-zero goals with jobs growth isn’t far-fetched, studies suggest. Modeling produced by the non-partisan firm Energy Innovation Policy and Technology LLC shows a plan for restricting global warming to 1.5 degrees Celsius could simultaneously increase U.S. gross domestic product by $489 billion per year in 2030 and $997 billion in 2050 (a 2.6% annual GDP expansion), creating more than 3.1 million new job-years by 2030 and 5.5 million new job-years by 2050.

Turning the Heat Off

In the process for developing more efficient housing and reduced emissions, government officials and energy experts call for greater electrification, which many see as key to decarbonizing. But making homes efficient enough to rely solely on sources such as electric heat pumps and technologies like PV requires significantly increasing airtightness and efficiency, experts point out. As homes are built and retrofitted for net-zero performance—many to levels such as Passive House standards—with or without codes, there are additional avenues through which windows could be drawn in, including better solar heat gain coefficient (SHGC) ratings.

While the focus among net-zero homes has traditionally been on U-factor ratings, among those reaching Passive House standards, “I tend to think that U-factor isn’t nearly as important as SHGC,” says Rich Williams, vice president of Alliance Green Builders in Encinitas, Calif., a net-zero and Passive House builder. “Passive houses are really good at retaining heat … they’re capable of being very comfortable in the heating season with very minimal use of heating systems. But what they discovered is that some of these houses were overheating.”

In those cases, the building envelope can be so efficient at retaining heat that with even the slightest amount of solar heat gain, “Suddenly they were having to apply cooling amid heating season,” Williams says. For this reason, in passive homes, “You want to control solar heat gain through glazing—basically try to make it zero,” he says. “Our philosophy is to go with the lowest SHGC you possibly can.”

In the past, that used to be 0.32 or 0.30 SHGC, he says, but “Now you can get down to 0.15, 0.12 or even 0.10 pretty easily,” he adds.

Regarding U-factor ratings, with or without stricter codes, “You’re only as good as your weakest point— especially if that weak point makes up a large part of the envelope,” Williams says. “We’re already insulating pretty well in the walls. And you have to think about whole assembly performance.”

To his point: In the average new home, 7% of surface area in exterior walls represents windows, yet, even at that rate, windows represent 48% of heat loss, LaFrance says.

Who Foots the Bill?

Of course, the cost for high-performance windows and other improvements also add to the price of new homes—at a time when builders already face issues of affordability. For this reason, some government officials have raised a red flag over current plans for reaching net-zero performance. For instance, though Massachusetts governor Charles Baker has made combatting climate change a red-hot goal for his state, “Our Commonwealth faces a housing shortage that threatens the future of families and businesses throughout the state,” he says. “My administration has heard significant concerns from stakeholders regarding the legislature’s proposal for a net-zero energy stretch code, which could slow the development of new housing while raising costs for Massachusetts families.”

But not all studies agree on the added costs. There are also indications that even if net-zero performance increases prices, consumers might be willing to foot the bill.

A study by the Massachusetts chapter of the U.S. Green Building Council suggests that zero-energy buildings are possible with no added upfront costs. A separate study, in neighboring Vermont, shows a 12% cost premium. Cost analysis performed through other case studies shows a breakeven point for energy upgrades in net-zero homes at 15 years for single-family and 19 years for small, multi-family buildings.

Whether or not upgraded windows factor into any of those studies is unclear, but a separate case study involving the Partnership for Income Restricted Housing Leadership (PIRHL), a Cleveland-based real estate developer and general contractor focused on sustainable affordable housing, calls out windows. The Cary Senior Living facility, a 62-unit senior housing complex in Cary, Ill., includes windows with simulated U-values of 0.13, officials say.

“With residents being aged 62 and older, and earning incomes at or below 60% of the area’s median income, the units had to offer a level of comfort and quality of life that is both sustainable and affordable,” says Mary Ellen Melcher, director of development project management at PIRHL. “The products we chose, including the Geneo window system [by Rehau], had to be able to help us achieve that end result.”

Another case study in Massachusetts shows the added cost for better windows to be fairly negligible, at an additional $689 for a 1,200-sq.-ft., zero-energy home, before any rebates and tax incentives, when compared to a similar home built to code. At the same time, the additional costs for zero-energy performance overall came to $40,393, or about 20% of the sales price. (After all tax rebates and incentives, the added costs came to about $9,000, or 4.6% of the sales price.)

But just as increased costs for lumber and other factors haven’t steered buyers away from new homes, there are indications that consumers are willing to pay for energy upgrades. According to research conducted by the National Association of Home Builders (NAHB) in summer 2020 and released earlier this year, a survey of more than 3,000 home buyers showed that buyers are willing to invest in features that help to lower their utility bills, with the average buyer willing to pay as much as $9,292 more for a home in order to save $1,000 annually.

With or without tax incentives and stricter energy codes, the role of windows in a drive toward zero emissions will ultimately lie in the hands of consumers and an industry that has to make its own way onto the field.

Drew Vass is the editor of [DWM] magazine.

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