GUARDIAN INSIGHTS

Choosing Glass

Woman by window

Navigating Today and Tomorrow’s Energy Codes

Although the United States and Canada are on different trajectories when it comes to residential building energy codes, and U.S. homebuilders that work in multiple states must deal with different regulations state-to-state, the residential construction industry seems to be on the same page about this: We’re heading toward higher performance requirements.

Energy Code Requirements

As the EPA prepares draft criteria for Energy Star Version 7, homebuilders want to prepare by identifying those products and systems that will help them deliver more energy-efficient houses. An interesting trend is the movement toward whole building modeling instead of prescriptive components to calculate energy performance.

Consider this: It may be more economical for a builder to install high performance windows than increase the amount of insulation. A total building design path provides more flexibility for builders to evaluate and select products and systems.

We’ve all spent an unprecedented amount of time in our homes in 2020, which has resulted in a new way to examine value: It’s not just about getting your money out when you sell your home; it’s about getting the most happiness and strongest sense of well-being out of where you are spending your time. The spike in home improvement spending bears this out.

While we prepare for the next round of energy code updates, it’s a great opportunity to examine how the right window product can help position a home to meet and exceed energy performance requirements.

The Role of Solar Control

The solar heat gain coefficient (SHGC) is the ratio of the sun’s electromagnetic energy that, upon reaching a window, is transmitted to the other side. The lower the SHGC, the less solar heat enters the home. The lower the SHGC, the less air conditioning may be needed to maintain a comfortable temperature on hot days, offering energy savings. Yet in particularly cold climates, windows with high SHGC values can help provide passive heating.

The optimal solution is climate-dependent, and also requires consideration of directionality: Recognizing the maximum solar exposure on the Southern elevation (within the Northern Hemisphere) and factoring the short-term near-horizonal exposures at the Eastern and Western elevations.

The Role of Insulating Performance

The insulating performance of a window refers to its effectiveness in impeding heat transfer because of an outdoor/indoor temperature difference. The U-value quantifies this performance by describing the energy transfer through a window relative to time, the surface area of the window, and the temperature difference. A low U-value indicates that a window is lowering heat transfer.

Regardless of the climate zone, a low U-value is generally advantageous to reduce energy losses and to provide better thermal comfort, in addition to protecting the interior of the home from the effects of the elements.

Selecting the Solution

Today’s high-performance windows are formulated to meet the solar control and insulating performance needs of differing climates while meeting and exceeding energy codes and guidelines. No matter the region or the intensity of the sun, there is a solution to help achieve the right balance.

The placement of coatings has an important role in energy performance. In cooling-dominant regions, a low-E coating on the #2 surface of a double- or triple-pane window is generally ideal. In heating-dominant regions, a low-E coating on the #3 surface of a double-pane window or the #5 surface of a triple-pane window can allow passive heating amidst insulating performance.

The Department of Energy’s Lawrence Berkeley National Laboratory Windows Group conducted a study to examine effects of increased window insulation, static and dynamic solar control and daylighting performance and concluded that the right combination of insulation, and dynamic solar control while maintaining visible transmittance can result in window net zero energy.

Homeowners and their architects can select the best energy saving glazing solution from the many high-performance options now available using Guardian data that references National Fenestration Rating Council (NFRC) window performance ratings. The ratings were developed using powerful software tools developed by the Berkeley Lab Window research team. Glass properties, energy savings and comfort improvements were validated in extensive field and lab measurements made by the Berkeley Lab team over many years, in part to validate NFRC simulation results.