A Look at Glazing in the New
by Thomas D. Culp, PhD.
SHRAE 90.1 is the predominant energy efficiency standard for commercial
buildings, and mid- and high-rise residential buildings over three stories.
States are required by federal legislation to consider its adoption, and
ASHRAE 90.1 is also referenced as a full compliance option within the
International Energy Conservation Code (IECC). ASHRAE 189.1 is a companion
standard for high-performance green buildings, using 90.1 as a basis,
but then also overlaying other “green” concepts such as site selection,
water use, material choice, daylighting, and indoor environmental quality.
ASHRAE published the new 2013 version of ASHRAE 90.1 last October, and
they are now finalizing the 2014 version of ASHRAE 189.1 to be published
later this fall. Overall, ASHRAE 90.1-2013 is estimated to be approximately
7 to 8 percent more stringent than the 2010 version, and approximately
38 percent more stringent than the 2004 version. A number of changes affect
fenestration, glazing and daylighting.
U-Factor, SHGC, VT/SHGC
The stringency of the prescriptive window requirements has been increased
in 90.1-2013. Overall, U-factors were lowered by approximately 10 percent
compared to 2010. Solar heat gain coefficient (SHGC) requirements stayed
the same, already set at appropriate levels for each zone. The new values
do not require triple glazing to comply, but will require low-E glass
everywhere (either for U-factor in the north or SHGC in the south), thermally-broken
frames in all zones but the far south, and higher performance frames and
argon gas filling in the north.
There is also a new minimum requirement for the visible transmission (VT)/SHGC
ratio in spaces where automatic daylighting controls are required. The
value was set to require solar selective glazing (whole product VT/SHGC
= 1.1 or center-of-glass LSG = 1.25), but to leave the final choice on
VT to the designer based on the daylight design, function of the space,
glare control, and other factors.
While it is still being finalized, it appears ASHRAE 189.1-2014 will simply
set the U-factor and SHGC requirements as 10 percent lower than ASHRAE
90.1, but the SHGC is only reduced on east and west facades, and no lower
There is significantly increased focus on daylighting in the new standards.
One small, but important, change is a new requirement that the daylight
zones be identified on submitted floor plans. This, hopefully, will encourage
architects and daylight designers to work together earlier in the design
process to optimize daylighting before the envelope configuration is locked
in place. It will also help with determining which spaces will require
automatic daylighting controls.
Additionally, following a cost effectiveness study, the toplighting requirements
in 90.1 have been expanded to require a minimum amount of skylights and
lighting controls in spaces more than 2,500 square feet with ceiling heights
over 15 feet, reduced from the prior threshold of 10,000 square feet.
Finally, the lighting control requirements were significantly rewritten
to require automatic daylighting controls in many more spaces (where the
combined general lighting power is greater than 150 W in the primary zone
or 300 W in the primary and secondary zones), and to require better multistep
or continuously dimming controls with a full-off state to maximize energy
“Recent proposals to reduce
the prescriptive window area limit were soundly rejected once it was
determined that reduced window area could actually harm indoor environmental
quality and occupant well-being.”
Both 90.1-2010 and 189.1-2011 included orientation requirements to encourage
designers to reduce energy and peak load by orienting their buildings
with the long sides of the building facing south/north when possible.
However, if a building does not comply based on its initial design, position,
and/or shading, then either the window area and location must be adjusted
(e.g. place more windows on the south, and reduce windows on the east/west),
or the performance path must be used to demonstrate compliance. Many designers
considered this section too onerous when considering real life practicalities,
so the language for 90.1-2013 and 189.1-2014 has been modified to provide
more flexibility including new options to use window SHGC and/or exterior
shading on the east and west to help comply.
No Reductions in Window Area
One very important item that was not changed is the prescriptive window
area limit. The window-to-wall ratio (WWR) limit in the prescriptive path
remains the same in both ASHRAE 90.1 and 189.1 at 40 percent WWR. Higher
window areas are allowed when equivalent performance is shown in the envelope
trade-off option or performance path.
In fact, recent proposals to reduce the prescriptive window area limit
were soundly rejected. They were rejected once it was determined that
reduced window area could actually harm indoor environmental quality and
occupant well-being, and be counter to high performance building design.
A number of research studies have shown that improved access and quality
of daylighting and views will benefit occupant productivity, health, and
well-being (see the information below).
The studies make it clear that design of high-performance spaces must
take a balanced approach to consider all factors including energy efficiency,
productive use of the space, and occupant health and well-being. One aspect
should not be traded off for another, and high-performance glazing products
help all these factors to be optimized.
Once the Department of Energy makes an official determination later this
year that ASHRAE 90.1-2013 saves more energy than the previous version,
all states are required to consider its adoption for use. States will
also start considering adoption of the 2015 IECC, which includes ASHRAE
90.1-2013, once it is published this spring. As with all building codes,
adoption will vary widely across the country. Some proactive states could
adopt it in January 2015, if not sooner. Other states will not make any
changes at all. Regardless, architects can already look to the new version
and start to use it in making design decisions.
ASHRAE 189.1-2014 will be published this fall, and it is also very likely
to be included as a full compliance option in the 2015 International Green
Construction Code (IgCC). As a green standard, ASHRAE 189.1 and/or the
IgCC will generally be used as a voluntary stretch standard, as an alternative
However, they could be considered for required use in certain state and
federal buildings, and the Department of Defense will look at incorporating
parts or all of these standards into its Unified Facilities Criteria requirements.
Let the Sun Shine In: Daylighting Benefits
20% increase in office worker cognitive test
21% increase in student test scores
6% increased retail sales
22% reduced development of surgical post-op
Reduced depression, improved sleep
Increased real estate value, rental rates15%
decreased absenteeism in office workers; Decreased office worker turnover;
39 additional work hours per year in office worker productivity; 9 to
16% improved performance on visual memory tests
Reduced length of hospital stay by 2.6 days
22% less pain medication in post-spinal surgery
Dr. Thomas Culp of Wisconsin-based Birch Point Consulting
is GANA’s code consultant and is engaged in the energy code process.
Architects' Guide to Glass & Metal
© 2014 Copyright Key Communications Inc. All rights reserved.
No reproduction of any type without expressed written permission.