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THE IMPLICATION OF ENERGY EFFICIENT
BUILDING ENVELOPE DETAILS FOR ICE AND SNOW
FORMATION PATTERNS ON BUILDINGS
N. Norris, D. André and P. Adams, M. Carter and R. Stangl
ABSTRACT
With advancements in building design in combination with changing weather patterns there is growing
concern over the increased occurrence of hazardous ice and snow formations and their potential release
from mid- and high-rise buildings. This concern is not only for the potential for building damage, but also
for the risk to commuters at street level if the ice should fall during their daily commute.
In cold climates, traditionally poor thermally resistant envelope assemblies readily transferred heat from the
interior conditioned space to the exterior surfaces of the building envelope, especially through glazing
assemblies. Glazed aluminum-framed envelopes (curtain wall/window wall) have become common for highrises and the building industry is currently moving towards using more thermally efficient versions of these
assemblies in order improve overall building energy performance. While improved thermal performance
for buildings is certainly a necessity, it can have unexpected consequences for ice and snow formation on
building exteriors that need to be considered. Over the past 20 years, significant progress has been made in
reducing heat transfer through glazing assemblies (vision and spandrels); however this reduction may be
causing colder localized exterior surface temperatures which, during wet winter precipitation events (wet
snow, sleet, freezing rain, etc.), contribute to more frequent hazardous ice and snow accumulation at these
locations.
This paper examines a case of an existing high-rise building where ice and snow formation and accumulation
was observed on both the vision and spandrel portions of the curtain wall system. It is believed that the level
of thermal resistance of these assemblies contributed to ice formation and accumulation that otherwise would
not have occurred to the same extent under the specific weather conditions present. A 3D finite element
thermal model was developed for the case building curtain wall assembly to simulate the conditions that
led to the observed ice formation and accumulation, using weather data representative of the site. Changes
to the thermal resistance of the glazing and framing system were evaluated to identify what effects they
have on the exterior surface temperatures and subsequently to ice formation and accumulation. Additional
mechanisms, such as building shape and solar radiation are also discussed.
INTRODUCTION
Winter storms bring wind, snow, sleet, freezing mist and freezing rain to bear on the building envelope. This
exposure creates performance challenges such as ice and snow buildup, that, if not anticipated and addressed,
can create a hazard to people and property below if this ice and snow falls from the building. The most often
reported incidents occur from mid- and high-rise buildings in populous areas where the heights of the
buildings can lead to more noticeable damage and there are more witnesses to falling ice sheets. This
typically coincides with significant public events or the daily commute in urban centers when there are more
people at street level.
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Ice and snow formations on tall buildings are not a new phenomenon. In 1939 the New York Times reported
on falling ice dropping off tall buildings in New York City, including the Empire State Building, after a
series of particularly wet snowstorms (Barbanel, 2014). Increases in heavy precipitation that have been
documented over the last decade have likely increased the number of icing events (U.S. EPA 2014). The
growth in high-rise construction, population densification and weather changes have all increased the
potential for hazardous falling ice incidents. In cases where injury or damage occurs, the incidents are often
kept confidential by building owners to avoid unwanted attention. As a result, the frequency of falling ice
events may not be evident to the design industry at large. Unfortunately, this frequency is difficult to quantify
beyond anecdotal evidence and injury reports (Dobnik, 2014). Nevertheless, the trend appears to be rising
based on media accounts and investigations by Northern Microclimate Inc. (Carter, 2012). These wet winter
precipitation events, have been reported as far south as Fort Worth, TX and Atlanta, GA, indicating that this
phenomenon is not unique to cold climates (Heinz, 2013).
This leads to the question of what factors influence ice
formation on buildings that are within our design control. While
there are many environmental impacts, such as solar exposure,
wind speeds and air temperatures; ice formation can also be
affected by the building design itself. Modern architectural
features and industry trends, such as solar shading devices,
protruding sills and mullion caps can all increase surface area
where ice and snow can accumulate (Stangl, 2014). One
industry trend that may be overlooked, however, is the impact
of improvements to the thermal performance of the building
envelope. The hypothesis is that some of these improvements,
while beneficial for reducing heat flow and energy costs, have
had the unintended consequence of lowering exterior surface
temperatures, thereby promoting an increase in ice and snow
formation at those locations that can release and fall.
PHOTO 1: FALLING ICE SIGNS A
GRIM REMINDER OF DANGER
ABOVE (STEINBERG, 2014)
With the increasing need for energy efficiency in buildings, the construction industry has been moving
towards improving the resistance to heat flow through the building envelope as a way of reducing the energy
consumed by space heating. One area that has made significant progress in this regard is glazing assemblies.
Although still generally far less insulating than opaque wall assemblies, the use of better reflective coatings,
gas filled insulating glass units (IGU) and additional panes have all reduced heat flow through glazing units
compared to those produced 15-20 years ago.
The case study in this paper details a sleet/freezing rain weathering event in which ice formation and ice
release was observed on several buildings in a dense metropolitan area. The study focuses on one of those
buildings, a newly constructed high-rise, where ice accumulation on the envelope was witnessed on multiple
occasions, including at the vision glazing. It is believed that the thermal resistance of the envelope,
specifically the glazing, played a direct role in the buildup of this ice and snow.
A 3D finite element thermal model of a typical glazed assembly from the case building was created to
simulate and evaluate the influence of the thermal resistance of the assembly on the mechanisms present in
the formation of ice during the weather event. The purpose of presenting this particular case is to raise
awareness within the design community of the potential for ice and snow buildup due to the influence of
building envelope assemblies and to promote further investigation. It is not intended to form an argument
against striving for improved energy performance in buildings.
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BACKGROUND: ICE FORMATION ON THE BUILDING ENVELOPE
Currently, building standards, such ASCE 7-10 – Minimum Design Loads for Buildings and Other Structures
(ASCE, 2013), refer to freezing rain and atmospheric icing with respect to their impact on the design of
“Ice-Sensitive Structures” (typically suspension bridges, communication towers, power lines, etc.). However,
it should be realized that structures not classified as “Ice-Sensitive”, such as high-rise or large roof buildings,
can still collect varying degrees of freezing rain or atmospheric icing. The collected ice can then become
hazardous to people and property below when released.
Predicting the potential for hazardous ice
formation on a building envelope is difficult due
to the variation in form, duration and intensity of
precipitation. Contributing to this complexity are
additional environmental influences of wind
speed, wind direction, solar exposure and air
temperature, along with the elevation, size, form,
shape, texture and colour of the building design.
These influences will not only affect the volume
of ice or snow formation, but also determine the
life cycle, transformation, and release of the
buildup from the building facade.
Regarding the interaction of winter precipitation
with the building envelope, in general heavy
PHOTO 2: SNOW BUILDUP ON
SILLS OR LEDGES
snowfall is most problematic for roofs, canopies,
and other low slope features where snowfall can
easily rest. However, it is less of an issue on vertical surfaces that work with gravity, such as windows, walls
and street level signposts. In order for vertical (or nearly vertical) surfaces to exhibit problematic
accumulation, specific types of precipitation need to occur. This includes wind driven wet snow, sleet,
freezing rain, and other forms of atmospheric icing (i.e. in-cloud or high elevation icing, freezing mist,
freezing fog, and hoarfrost) that can collect directly onto vertical and steeply-sloped surfaces of high-rise
buildings. These formations can either freeze on contact to surfaces that are below 0oC (32oF), or melt on
contact with warmer surfaces, then drain down the façade with gravity until reaching a surface with a
temperature below the freezing point, causing re-freezing and ice formation. Variations in the atmosphere
during a particular weather event (i.e., a storm driven temperature inversion, supercooled wind-driven
droplets, etc.) affects the form of the precipitation, which in turn influences how easily the precipitation can
adhere to surfaces. The types of winter precipitation that are most problematic for ice accumulation typically
occur when air temperatures are at or just below 0oC (32oF).
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PHOTO 3: ICE ACCUMULATION IN
MIDDLE OF GLAZING AT AN
OBSTRUCTION
PHOTO 4: ICE ACCUMULATION ON
A GLAZING OVERHANG
Examples of wet wind driven snow, sleet, and freezing rain adhering to cold building surfaces are shown in
Photos 3 and 4. Photo 3 shows how precipitation can freeze at a location where an internal structure obstructs
warm interior air flow in the vicinity of the glass. Photo 4 shows a glazing panel that extends from a vision
section to a soffit. In this particular case, a freezing line is clearly evident where the glass bridges from the
interior heated space to the unheated soffit space. From both these photos it is also apparent that melt water
produced from the adhered and melted wet snow above has run down the glazing surface and refroze,
forming a thicker ice mass. This ice mass is more likely to release from the glazing in a larger, more
hazardous form once the skin temperature behind the ice climbs above the freezing mark.
Thus, to create the particular condition discussed, a specific alignment of warm and cold exterior building
temperatures, combined with air temperatures around 0oC (32oF) that promote wet winter precipitation, need
to occur simultaneously. Of these, only the building skin temperatures have some degree of control through
design and operation of the building. This is analyzed further through the following case study.
CASE STUDY DETAILS
In the winter of 2011, a major urban center on the east coast of the United States experienced a night of
snow, freezing rain and sleet with morning fog and mist. In the morning, as air temperatures warmed to just
above 0oC (32oF), falling ice from bridges and some of the taller buildings were being reported within the
city. The reports continued for a 3-day period as further snow/sleet precipitation occurred and air
temperatures fluctuated around 0oC (32oF). The case study building, a 700ft+ office tower, was one of the
buildings that experienced issues with ice formation during this period. Falling ice and snow was reported
from different portions of the building facade. Remarkably, it was specifically reported that ice sheets had
formed in the middle of the vertical vision glazing, which is traditionally unusual for non-sloped glazing
systems. From eye-witness accounts, ice formed in the center of the glass, then released and slid vertically
from the façade. Falling ice sheets were numerous enough that spectators below could hear them hitting
against neighboring buildings high up in the fog.
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The case building was relatively new at the time of the snow/sleet event and was noted for its energy efficient
design, including a high thermal performance curtain wall system that comprises most of the building façade.
Other influencing factors such as internal air temperatures, night time set-back strategies, local microclimate
influences due to elevation and wind influences, etc., are unknown, limiting the accuracy of the case study
results presented.
CASE STUDY THERMAL MODELLING
To determine if the exterior surface temperatures and thermal performance of the envelope played a role in
the formation during the snow/sleet weathering event described above, a thermal model was developed for
the curtain wall system (vision and spandrel). The purpose of this analysis was twofold:
1. To calibrate and compare the model to the real observed conditions to determine if the exterior
surface temperatures of the curtain wall could have played a role in ice formation;
2. Once calibrated, to use the model to see how sensitive the potential of ice formation is to
adjustments in the thermal resistance of the curtain wall system.
The model was created using 3D heat transfer software from Siemens called Nx. The modeling procedures
and software were extensively calibrated and validated as part of the ASHRAE 1365 research project, which
analyzed various building systems for thermal performance (Morrison Hershfield, 2011). The curtain wall
included both vision and insulated spandrel sections, representing one full floor height, as shown in Figure 1.
The curtain wall was a unitized system with the vision and spandrel glazing held in place with 4-sided
structural silicone. This configuration offers better thermal performance than pressure capped systems. The
IGU was double glazed with a 0.04 low-e coating on surface 2 of the outer pane, and a fritting pattern
installed using a window film. The IGU had a center of glass U-value of 1.7 W/m2K (0.30 Btu/ft2hr°F).
Additional components for the assembly include 4” of mineral wool, equivalent to R-16.8 (2.96 RSI) in the
backpan, polyamide thermal break extrusions and a suspended floor and ceiling, instead of a knee wall (pony
wall). Other vision and spandrel glazing characteristics are comparable to systems used on similar newly
constructed high-rise buildings in North American cold-climate cities. Altogether, the curtain wall system
is considered a “good” thermally performing curtain wall system.
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FIGURE 1: MODELED CURTAIN WALL WITH VISION AND SPANDREL SECTIONS WITH
A RAISED FLOOR
Weather data was collected for the case building site from local weather stations during the 3-day period in
which the snow/sleet event occurred. This included exterior air temperatures, solar irradiance, wind speeds
and exterior relative humidity. Using this weather data, a transient analysis was performed on the system
over the 3-day period, along with the following assumptions:
• Interior temperature was 21°C. It was assumed the air was well mixed.
• Most material properties were considered constant and taken at 21°C, except for aluminum and air,
which were temperature dependent.
• Sky radiation, (night sky and cloud cover) was included using the Stefan-Boltzmann law and
Swinbank formula for long wave-radiation
• Exterior air film coefficients were varied to match the collected wind speed data.
• Interior air film coefficients were taken from ASHRAE Handbook of Fundamentals (2013).
The model did not take into account wind speed and direction, specific interior heating distribution systems
or the effects of latent heat. Latent heat will be absorbed or released during freezing and melting of ice but
does not result in a temperature change. Snow buildup on the glass may also insulate the surface, changing
air films and effectiveness of the low-e coating, however, the transient model was simulated at one hour
time steps and it was assumed that these effects would be minor in comparison to the effects of changes in
the exterior air temperature.
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CASE STUDY THERMAL MODELLING RESULTS
The exterior surface temperatures for the vision glass and the spandrel glass were simulated over the
3-day period. It was assumed any surface below 0oC (32oF) was considered at risk for ice buildup from
sleet/freezing rain. Figure 2 shows the simulated surface temperatures for the vision and glazing sections
for surfaces below 0oC (32oF) for the first 16 hours of the recorded snow/sleet event. Each image in the
sequence is centered on a section of the spandrel, with vision glazing shown above and below (similar to
Figure 1).
FIGURE 2: SURFACE TEMPERATURE PROFILES OF THE MODELED CURTAIN WALL VISION
AND SPANDREL SECTIONS OVER THE FIRST 16 HOURS OF WETTING EVENT FROM THE
CASE STUDY.
Comparing the colour contours to the surface temperature scale in Figure 2 it can be seen that during the
bulk of the snow/sleet event in the first 16 hours, the spandrel remains consistently below 0oC (32oF). While
this makes it more likely that sleet/freezing rain could build on that surface, it also gives solar radiation an
opportunity to melt that buildup from the outside. With the vision glass there is only a short period of time
(3 hours) where the surface temperature is below freezing. In this case, sleet/freezing rain could stick to the
vision glass, but then release as the surface temperature is raised back above the freezing mark, or melt and
re-freeze on the colder portions of the spandrel. It is also worth noting that Figure 2 also shows the majority
of the mullion framing is above 0oC (32oF) throughout the studied period, except for small areas at the center
line of the mullion.
Figure 3 shows the exterior air temperatures and the exterior surface temperatures for the center of the vision
glass and center of the spandrel glass, along with the vision and spandrel frame temperatures. The center of
glass is the likely location of the coldest surface temperatures since they are areas farthest from the effects
of thermal bridging through the edge of glass and mullions. Note that these center of glass values do not
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directly indicate the size of the areas at that temperature, however it can be inferred that the colder the center
of the glass value, the larger the area on the glass that is below 0oC (32oF).
FIGURE 3: MODELLED EXTERIOR CENTER OF GLASS AND FRAME SURFACE TEMPERATURES
FOR VISION AND SPANDREL SECTIONS COMPARED TO WITNESSED PRECIPITATION AND
FALLING ICE
From Figure 3, due to the conductivity and specific heat of the materials used in the assembly (mainly
aluminum) there is no advantage of heat storage in the system when air temperatures are above 0oC (32oF).
The vision and spandrel center of glass temperatures follow the exterior air temperature, only transposed
higher with minimal lag in response. Night sky radiation could also increases the risk of exterior frosting
from condensation by making exterior surfaces colder than the surrounding air temperatures, however due
to the cloud cover during the case weather event, the effects of night sky radiation was minimal. The
simulated surface temperatures do not drop below the air temperature, which indicates that the ice buildup
for this case is a result of precipitation, and likely not from condensation. However, this mechanism should
not be discounted in general, as the conditions for exterior frosting from condensation may occur during
cool days with clear night skies. Note, however, that due to cloud cover during precipitation events, it is
highly unlikely ice formation from both precipitation and condensation could occur at the same time.
These results were compared to the timeline of events for the case study period, which included when falling
ice was observed onsite; witness interviews and media reports (also shown in timeline in Figure 3). Between
approximately 3:00am to 6:00am on Tuesday morning, the meteorological reports recorded precipitation
containing freezing rain and or other wet winter precipitation, during which the 3D Thermal Modelling
results predicted that the vision glass surface temperature would dip below 0oC (32oF). Subsequently, falling
ice sheets were reported during the early morning after 7:00am and coincided with raising air temperatures.
This matched with increased vision glass surface temperatures above 0oC (32oF) shown in the 3D model.
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Finally, the 3D model results indicate that the spandrel segments of the curtain wall glazing did not rise
above the freezing mark until approximately 8:00am on Wednesday, when further falling ice was witnessed
and reported. Overall, this indicates that the model was generally able to capture the icing event.
MODEL SENSITIVITY TO SURFACE TEMPERATURES
Knowing that the model was able to simulate similar conditions as those seen in the case study, several
aspects of the curtain wall system were modified in the model to examine the sensitivity of the thermal
performance of the assembly on the exterior surface temperatures of the vision and spandrel glass. This
analysis helps establish the strength of the connection between the envelope thermal performance and
ice formation. Two aspects in the model were adjusted for analysis: the IGU performance and the
frame/insulation performance. The scenarios are described in the following sections and the results are
further analyzed in the Discussion portion of the paper.
Figure 3 shows that, while there was no precipitation, Thursday had the largest fluctuations in air
temperatures around 0oC (32oF). As such, Thursday’s exterior conditions were used as the basis of the
sensitivity analysis as a worst case scenario had there been sleet/snow precipitation.
IGU Performance
Coatings on glazing units have steadily improved since the introduction of low-emissivity coatings and gas
fills (Wilson, 2012). These coatings reduce the radiative heat transfer through the glazing depending on the
emissivity and placement of the coating within the IGU, while gas fills can greatly reduce the conductive
heat flow through the gap between glass panes. For the base system, the glazing had a 0.04 low-e coating
on surface #2 with a 15mm airspace. Three adjustments to the base system were tested: 1) The coating
emissivity was increased to 0.20; 2) The low-e coating was removed; 3) The IGU gap was filled with a 90%
Argon gas mixture and a 0.04 low-e on surface #2. The surface temperatures for these scenarios are shown
in Table 1.
TABLE 1: EXTERIOR SURFACE TEMPERATURE RESULTS FOR VARIOUS GLAZING COATING
CHANGES
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Frame/Insulation Performance
With spandrel panels, designers often attempt to increase the thermal performance by increasing the amount
of insulation located in the spandrel backpan. Unfortunately, due to the amount of thermal bridging from
the mullions that bypass the insulation, the overall thermal resistance through the system is often not
significantly impacted. For the case system, there was 4” of mineral wool insulation with additional
insulation wrapped at the mullions, and large thermal breaks. For this sensitivity analysis, two adjustments
were made to the curtain wall system: 1) The amount of backpan insulation was reduced to 2” of mineral
wool and the mullion wrap was removed, 2) The thermal breaks were reduced in size and made of a more
thermally conductive material. The surface temperatures are shown in Table 2.
TABLE 2: EXTERIOR SURFACE TEMPERATURE RESULTS FOR VARIOUS INSULATION CHANGES
DISCUSSION
From the sensitivity analysis in Table 1, there is an argument to be made that increasing the thermal
performance of the IGU’s in the vision portions of the curtain wall will decrease exterior surface temperatures
and contribute to ice formation. However, from Tables 1 and 2, the center of the spandrel surface
temperatures remained unaffected by the changes to the glazing, insulation levels and thermal breaks. Note
that these were center of glass surface temperatures, and the decreases to the insulation and thermal breaks
showed exterior surface temperature increases at the mullions, but not in the field of the spandrel. This will
result in less surface area of the glass below 0oC (32oF) available for icing due to the edge effects, depending
on the spacing of the mullions. There is still a potential that the ice thickness could increase at the transition
between the warmer and colder areas of the glass, as shown in Photographs 3 and 4.
For the vision glazing, with a less effective low-e or no low-e coatings, the exterior center of glass surface
temperature is increased up to over a degree. While this may seem small, the ice formation observed in this
case study occurs with specific types of winter precipitation, (ie. Wet wind driven snow, sleet, and freezing
rain), which typically occur within tight temperature ranges at or just below freezing. Small increase in
surface temperatures may be enough to reduce the size of ice formations, significantly lowering their
potential to be hazardous. This supports the idea of why previously, before low-e coatings under 0.20, ice
buildup on the envelope may not have been as prevalent.
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Using argon gas fill for windows instead of air can greatly decrease heat flow through IGU’s, and are
becoming more common as prices decrease. From Table 1 it can be seen that the heat reduction from using
Argon gas can also greatly reduce the exterior surface temperatures. As these gas fills for IGU’s become
more standard on projects, the icing problem could potentially increase.
With a large amount of new high-rises being built in cold climate cities like Toronto, Chicago, Boston, and
New York, the question may be asked, why is this not happening on other buildings? As discussed in the
introduction, it very well may be happening on many other buildings, however it may not be as noticed or
there are factors that could play a significant mitigation role in other buildings. It is important to note that,
while there has been a large amount of new construction in these cold climate cities, there is still a significant
amount of older building stock that have glazing over 20 years old. It is unlikely that the glazing in these
buildings have been replaced unless they have gone through a major retrofit. First Canadian Place, built in
1975 before the introduction of low-e, had only 30% of its windows replaced by 2010 (Davey, 2010). As a
result, there are many tall buildings which still have substantial heat loss through the glazing, keeping the
exterior surface temperatures warmer. While it is likely the IGU performance did play a role in the ice
formation on the case building, there are many other factors that can also contribute to or oppose ice
formation on other buildings that could be explored with further study.
One major influence on ice formation on glazing may be the layout and design of the HVAC systems in use,
specifically the method and location of supply of the warm air to the interior. Any system that does not
provide or is prevented from providing a uniform heat and air distribution risks cold spots or delayed
response to temperature fluctuations at the window exterior. Natural convection heaters (like electric
baseboards) placed at the base of windows will warm the glass and cause the hot air to rise and cool as it
touches the window, creating a temperature gradient along the surface. This will impact the freezing pattern
on the exterior of the glass. Forced air systems distribute the air through diffusers and returns. This is often
helpful in cold climates to prevent interior condensation, however can be obstructed by desks or partitions,
creating cold pockets.
Considering trends in architecture, many modern designs include highly sloped walls, wing walls or double
facades along with features such as protruding mullion caps, fins or architectural screens not typically seen
in previous construction. These design elements all increase the amount of cold surfaces on which ice and
snow can form. In contrast, older designs were less angular and more likely to be constructed with stone or
simple metal window sills. Older high-rise towers using concrete or other masonry can retain heat stored
from sunlight, or from the building interior, which could assist in maintaining warmer surface temperatures
during a sleet/freezing rain event. As a further avenue of study, it would be interesting to observe if metal
cladding assemblies are also experiencing issues with ice formation as they are often higher in thermal
resistance than spandrels and also have a smooth exterior exposed to ice and snow.
The height of buildings and local density could also explain why some buildings may experience more icing
events than others. If the building is taller than the surrounding buildings, the upper floors are exposed to
greater amounts of wind driven precipitation, with higher wind speeds and colder air temperatures than that
experienced at grade level. Lower buildings are more sheltered from air movement and can benefit from
higher local air temperatures due to the density of the buildings and human activities at street level, otherwise
known as the heat island effect. During low hanging freezing mists, these lower buildings may still be
susceptible.
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A major environmental influence on ice formation is solar radiation. Depending on the cloud cover during
a precipitation event, solar radiation can help keep a surface heated. Buildings that are oriented to take
advantage of more sunlight during the winter may have less of an issue. With ice exposed to solar radiation,
ice formation has a higher likelihood of melting from the outside, resulting in a more gradual melt and
reduced potential of the ice releasing off the glass in sheets. Regarding the influence of wind, without strong
winds, it is less likely precipitation will be driven onto the cold surfaces of the building.
PHOTO 5: EXTERIOR
CONDENSATION ON A
BUILDING FACADE
For this cast study, frost from condensation was not an issue. The
possibility of ice formation due to condensation under some
circumstances cannot be fully discounted, particularly if exterior
skin temperatures might be colder with newer glazing systems,
placing them more frequently below the ambient dew point
temperature when there is night sky radiation. Photo 6 shows
condensation and frost formation on the exterior of a triple glazed
system and metal panels. Exterior frost does not typically lead
directly to falling ice, however it does provide a colder surface for
sleet and freezing rain to adhere to if a precipitation event follows
a night of clear skies.
While not a feature in this case study, there is “self-cleaning” glass
available from glazing manufacturers which create a more
hydrophobic or hydrophilic surface. These exterior coatings
change the surface tension and can affect precipitation in different ways, which may also affect how ice
forms on glass, however to the best of our knowledge this has not been investigated or studied. While mainly
for specialized glazing, such as air traffic control towers or high-end penthouses, if this becomes more
prevalent in the building industry for high-rises, further research may be warranted.
CONCLUSIONS
With so many competing influences at play on the building envelope, it is difficult to pinpoint the direct
cause of ice formation for a specific event. For the case building, it was likely a combination of several
factors, including the thermal resistance of the IGU, that lead to the ice formation and release. The modelling
has shown in general that restricting heat flow, particularly through the IGU, can produce colder exterior
surface temperatures that can contribute towards ice formation. In the end, the intent of this paper is not to
state that thermal performance of the envelope of mid- and high-rise buildings is a leading cause of ice
formation, but it should be considered alongside other factors in design.
In terms of what can be done in design, reducing envelope thermal resistance is not desirable (no one wants
to go back to not using low-e coatings or gas fills). It may have to be accepted that, under certain weather
conditions, new highly glazed mid- and high-rise buildings may be at higher risk for ice formation. It is
possible that the implementation or avoidance of certain design geometries, HVAC strategies, or curtain
wall configurations in some geographic regions, could significantly reduce the potential for the localized
melt and refreeze of wet winter precipitation on façade surfaces, such as the vision glass, that can be
responsible for the most hazardous ice build-up and release. During the early design phase, options such as
podiums, canopies, or alternate building geometry over critical pedestrian or accessible areas should be
considered. Alternatively, it may be possible and become necessary to reduce icing potential through timely
building operational strategies that would avoid night time set-backs prior to storm events or temporarily
increasing internal air temperatures during wet precipitation events.
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Given the increases in severe winter weather over the last decade, future icing events are likely to be more
frequent and prolonged, increasing the potential for hazard. It is important to note that this paper analyzes
one occurrence of this phenomenon; however, there is a need to review additional buildings and other
documented icing events to achieve a better understanding of factors that can lead to formation and release
of ice and snow from the building envelope. The analysis of wind patterns, the influence of neighboring
structures in close proximity to a facade, building orientation, and other complicating factors were outside
the scope of this paper, but may have also played a significant role at the study building. Given the increasing
magnitude of the surface areas of high-rise buildings and the hazards that are associated with falling ice,
this is an issue that warrants further attention.
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