by Helen Sanders

Deployment and adoption. These are major challenges in getting high-performance envelope solutions into new and existing homes and buildings in the U.S. Deployment is a key focus of the U.S. Department of Energy’s (DOE) Building Technologies Office (BTO) programs, driving work at the National Laboratories and their partners.

Last week, I was fortunate to be invited to be on the peer review panel for their windows technologies program. I was struck by the array of challenges in envelope technology deployment in homes, especially in poor and disadvantaged communities. This month, I dive into just some of the great work that DOE and the National Laboratories do to overcome these challenges and identify opportunities for us to support.
Improving the performance of windows is critical for energy saving, decarbonization, resilience, human health, comfort and well-being.

The Data

Let’s start with some numbers. According to the DOE BTO for the residential single-family home sector:

• Windows represent about 8% of the exterior envelope but are responsible for 45% of the heat transfer and 25% of the home’s heating and cooling;
• There are 1.4 billion windows in the U.S. residential building stock; There are 48 million homes with single-pane glazing;
• More than 50% of homes have inefficient windows (single-pane plus poor dual-pane systems; and
• Yet only 2% of homes undergo window replacement each year–primarily because it is cost prohibitive.Only 2% of homes undergo replacement each year–primarily because of the high cost.This is not just a carbon emissions problem but a critical resilience, human survivability and health problem.

In severe weather events with accompanying power outages, poor-performing envelopes limit the ability for families to safely shelter in place since their homes will quickly overheat or get too cold for human survivability. Recall the winter storm of 2021 in Texas and the heat dome in the Pacific Northwest the same year, during which deaths spiked due to temperature extremes.

Thermal discomfort, condensation causing mold and poor acoustics lead to poor health and well-being. In addition, large heating and cooling loads are a barrier to heat-pump deployment and a decarbonized grid.

Additionally, the poorest-performing homes and multifamily apartments are aggregated toward low-income segments of the population, accentuating health and economic inequity.

BTO’s Goals and Targets

DOE BTO’s role in delivering a net-zero U.S. building sector by 2050 is to “support rapid decarbonization of the U.S. building stock in line with economywide net-zero emissions by 2050, while centering equity and benefits to communities.” It is doing this by (i) increasing building energy efficiency, (ii) prioritizing equity, affordability and resilience, and (iii) reducing residential carbon footprint and energy consumption.

The initial envelope design target for homes is an R-value of 19 (R-19). According to the team at Pacific Northwest National Laboratories (PNNL), “We have seen higher efficiency standards for building envelope components in the International Energy Conservation Code (IECC); the 2021 version has insulation at around R-60 for ceilings and R-20 for wall cavities, but windows are still around the R-3 level.” This achieves an overall envelope performance of R-10.8, far from the R-19 target.

Higher-performance windows must be installed to enable getting to this target. PNNL demonstrates that wall insulation would have to be at an unfeasible R-330 if windows stayed at R-3, concluding that the upgraded envelope is unfeasible without R-5 windows (U=0.20 BTU/of.hr.ft2). At this level, the insulation would need to be a more feasible R-38.

Because of the large opportunity at the existing building level, upgrading the current building stock is a large focus for DOE. To address cost- effectiveness barriers, it is focusing on deploying lower-cost options such as storm windows and insulating panels (SWIP), achieving R-5 windows through thin-triple insulating glass (IG), and adding insulation when re-siding (AIRS). It also specifically evaluates technology and support options for and targeting engagement and outreach in disadvantaged communities.

Not Your Grandma’s Storm Windows

According to DOE, modern storm windows are not your grandma’s storm windows! Apparently, storm windows have an image issue as the name is associated with unattractive and inoperable storm windows of the past. There is also much misinformation about payback, condensation and applicability. Modern storm windows are much more attractive, can be operable and are designed to be permanently installed.

Being installed on the outside or inside, they reduce air leakage by creating an additional air barrier and further decrease heat loss by creating an insulating cavity against the existing window. Hard-coat low-E coatings are often used to promote better insulation. Work by Tom Culp, Birch Point Consulting, and Katie Cort, PNNL, in 2014 showed that they offer similar energy savings to full window replacements (10-30% annual energy savings), but at about one-third the cost!

A lack of awareness of these features and benefits is hampering widespread deployment. Currently, few utility incentives or weatherization programs include storm windows, and they are not consistently included in the toolkit of offerings of home performance contractors.

Also, little known is that they come with validated performance ratings from the Attachment Energy Rating Council (AERC), just like regular windows have performance labels from the National Fenestration Rating Council (NFRC). There are also Energy Star-certified storm windows!

PNNL has launched a campaign to educate and support utilities in developing incentives, help weatherization organizations to include storm windows, and encourage manufacturers to rate their products through AERC and Energy Star.

R-5 Window Deployment

To overcome the thickness and weight challenges that conventional triple-pane glazing presents for existing windows, DOE is actively supporting thin triple-pane insulating glass. Very thin glass (~1mm/0.03-in) is used as the middle lite, with two low-E coatings (surfaces 2 and 5). The smaller cavities are krypton-filled (cost permitting). This is believed to be an easy “drop-in” solution for current window frame designs, in the same way as low-E coatings were when first introduced. Addressing this barrier, the hope is for faster adoption of R-5 windows. It leverages the glass technology development already done for the flatscreen display market, which has been taking thin glass to increasingly larger sizes.

Currently, the National Laboratories are tag-teaming the work, with the windows group at Lawrence Berkeley National Laboratory (LBNL) working with manufacturers to drive product validation and availability. PNNL is working on addressing market barriers through market analysis, cost- effectiveness evaluations and field performance validation, including validation of the co-benefits of condensation reduction, thermal comfort and acoustics, plus the “drop-in” feasibility. The new ENERGY STAR v7, which will drive triple pane in the northern zone, will be used as an accelerator for the thin-triple deployment.

Adding Insulation When Re-Siding (AIRS)

In existing homes, walls are a problem, too. Work by PNNL has shown that adding 1-inch, R6.5 exterior insulation with air-sealing to an uninsulated wood-framed house saves between $240 and $700 annually in hot-dry and cold climates, respectively. Field studies by PNNL demonstrate a marked improvement in interior comfort, improved ability to maintain temperature set points and quietness.

DOE believes that the re-siding event in a home’s lifecycle is an entry point into the widescale adoption of exterior continuous insulation and air-sealing. If a homeowner is going to invest in re-siding their house, then why not add insulation at the same time? Unfortunately, while 3.5 million homeowners invested in siding projects in 2021 (~$4B sq.ft.), only 10% of re-siding added 1 inch or more of continuous insulation.

Rigid exterior continuous insulation is added under the new siding and taped to provide a weather barrier and air seal. Sounds simple. However, with a large variety of starting conditions, contractors find it slow and complex (because it is new and different). In the context of the recent boom in new construction where siding is faster, easier and has larger margins, contractors are reticent to expand their scope from fast and basic to slow and cumbersome.

Currently, PNNL is working to overcome these barriers by engaging influencers and alternative messengers such as homeowners’ associations, insurance adjusters, etc. The team also is looking for volunteers to participate in the field study work who will receive free insulation and air sealing worth an average of $4,000 per home. If you want to re-side your house and support decarbonization and resilience strategies, this might be an opportunity you can’t afford to pass up!

Helen Sanders, Ph.D., is a general manager at Technoform North America.