ASHRAE Journal - March 2022 - 60

TECHNICAL FEATURE
comfort, both in terms of temperature and acoustics.
In this regard, the added performance of high R-value
windows is viewed favorably in terms of providing noticeable
added comfort to the occupant. Because the current
code leaves the window as the relative " hole in the wall "
in terms of thermal performance, the act of nearly doubling
that R-value by upgrading from double- to triplepane
windows adds noticeable thermal and acoustic
comfort improvement to the home, as well as nearly
eliminating the potential for mold growth from roomside
condensation on the window.6 From the builder
perspective, these are all immediately tangible selling
points. In addition, builders have noted that higher
performance windows enable them to use shorter HVAC
duct runs and interior duct throws as well as downsize
HVAC equipment,3 which provides builders more flexibility
in design and additional options to reduce costs.
Material Costs
In almost all cases, first costs, or the incremental cost
of triple-pane versus double-pane window, are cited
as the primary reason why builders do not upgrade to
higher performing windows. As previously discussed,
the cost of triple-pane windows can be prohibitive for
some projects. However, window prices vary significantly,
and as triple-pane windows become more widely
available, prices will come down. Recent market studies
suggest that a cost increment of $3/ft2 to $10/ft2 ($32/m2
to $108/m2) is currently attainable. For our prototype
home, this would equate to a $700 to $2,400 incremental
material cost to upgrade the windows, which is not
trivial, but about the same as added continuous wall
insulation costs for the same home.
Installation Costs
Some of the first-generation triple-pane windows on
the residential market (and some European models) are
considerably heavier than double-pane windows such
that installation sometimes required additional labor
and special equipment including cranes or forklifts.
In the U.S. market, many triple-pane window models
are lighter weight with slimmer profiles. Recent field
studies (Figure 2) indicate that no additional labor or
equipment is needed for the installation of thin triplepane
windows. In contrast, many of the wall insulation
upgrade options discussed here will require additional
training and labor to implement.
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ASHRAE JOURNAL ashrae.o rg M A R CH 2022
Other Costs
In addition to the material and installation costs, there
can be associated difficulty factors, learning costs and
risks associated with the installation of various envelope
components and associated construction techniques.
For example, the conversion from 2 × 4 to 2 × 6 wall construction
has been associated with a significant learning
curve. Likewise, although it has been demonstrated that
air leakage rates can be achieved at a minimal incremental
cost when best practices are used, human error
is a fact of life on the build site, and even small errors
could potentially increase the risk of not achieving these
air leakage targets. The troubleshooting that may be necessary
to correct these errors, particularly after sheetrock
has been installed, can be very costly. In contrast to
some of these risks and construction hassles, the choice to
move to a better window carries relatively little risk, as
the installation is the same, and provides some " insurance "
against the risk of not meeting air-sealing targets.
Acknowledgment
The authors acknowledge Tom Culp, Ph.D., Member
ASHRAE, of Birch Point Consulting for his review and
consultation related to IECC compliance pathways and
trade-offs. Terri Gilbride and Robert Salcido of Pacific
Northwest National Laboratory provided reviews of the
analysis and updates related to the residential envelope
provisions of the 2021 IECC. This work was supported
by the Assistant Secretary for Energy Efficiency
and Renewable Energy, Building Technologies Office,
of the U.S. Department of Energy under Contract No.
DE-AC02-05CH11231.
References
1. Hart, R., S. Selkowitz, C. Curcija. 2019. " Thermal performance
and potential annual energy impact of retrofit thin-glass triple-pane
glazing in U.S. residential buildings. " Build Simulation 12(1):79 - 86.
2. NFRC. 2020. " NFRC Certified Products Directory. " National
Fenestration Rating Council. https://tinyurl.com/2p8c6n7b
3. Gilbride, T.L., S. Selkowitz, O.G. Dingus, K.A. Cort. 2019. " Double
or Triple? Factors Influencing the Window Purchasing Decisions of
High-Performance Builders. " PNNL-28809. Pacific Northwest National
Laboratory, prepared for the U.S. Department of Energy.
4. Hart, R., S. Selkowitz, M. LaFrance, K. Cort, et al. 2020.
" Innovative Market Pathways to Promote Adoption of HighPerformance
Insulating Windows. " ACEEE Summer Study Proceedings.
5. Hudson, E. 2019. " Increasing Costs, Skilled Labor Shortage,
Airtightness Pose Builder Challenges. " Home Innovation Research
Labs.
6. Hunt, W.E., S.I. Rosenberg, K.A. Cort. " Evaluation of Thin TriplePane
Windows in the PNNL Lab Homes. " PNNL-31165. Pacific Northwest
National Laboratory, prepared for the U.S. Department of Energy.
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