On Thin Ice: Snow Load
Management and Mitigation
UNDERSTANDING APPROACHES AND BEST PRACTICES.
E
ach year, property owners and
facilities managers across the
United States face damage from
snow and ice accumulation on their roofs.
Winter precipitation can quickly reach
critical limits resulting in a partial or
complete structural collapse. Snow loads can
also cause damage to electrical conduits,
natural or propane gas lines, water or fluid
piping, and other rooftop accessories.
With reports predicting colder-than-normal and
wetter-than-usual conditions for 75% of the
country east of the Rocky Mountains, the 20142015 winter season will challenge current snow
load management practices.
Location
Avg Winter Temp
Total Snowfall
29.9°F
56.4”
Boston
26.4°F
50.1”
Hartford
32.9°F
57.3”
New York City
31.3°F
60.5”
Newark
33.0°F
59.5”
Philadelphia
33.3°F
26.9”
Baltimore
32.8°F
33.0”
Washington D.C.
18.8°F
67.3”
Chicago
24.2°F
52.5”
Indianapolis
Table 1. 2013-2014 Average Winter Temperature and Total
Snowfall1
Although structural collapses are a poignant
example of the concerns facing facility managers
during the winter, rapid changes in temperature
and winter precipitation can lead to a variety of
© 2014 Low-Slope Solutions
other concerns including roof leaks, snow drifts,
and icicle formation.
Roof leaks are one of the most common winter
hazards facing property owners and facility
managers. As snow melts and refreezes into ice,
leaks may occur. Because of building geometry,
cold spots on the roof can cause ice to
accumulate. As ice forms on the walls and around
the drainage area, water may further backup into
the roof system causing leaks on the sales floor.
The combination of liquid water and ice may
cause physical damage to the structure and
subject tenants and customers to slip hazards.
Uncontrolled moisture infiltration has the
potential to destroy finishes, damage equipment
or product, and support mold and fungi growth.
The formation of snow drifts can also be
problematic for facility managers. Damage to
rooftop accessories, curbs, and equipment are
possible as drifts slide down slopes and off the
roof area. Falling snow is dynamic, spontaneous,
and dangerous to tenants and pedestrians.
Damage to landscaping, cars, and equipment is
also possible and carries with it the risk for
increased maintenance costs in the spring. Large
snow drifts should be reduced as soon as
conditions allow.
Although icicle formation is a normal part of the
snow melting cycle, the formation of icicles over
high traffic areas may result in property damage
and injuries to customers. Conditions that allow
icicle formation over sidewalks, entries, parking
lots, and vehicular paths should be considered
unacceptable and mitigation techniques should be
used to reduce liability and structural concerns.
On Thin Ice 1
LOW SLOPE ROOF SYSTEM AND SNOW
The likelihood of experiencing structural damage
from snow-induced overload varies with the type
of roof structure, design loads, and weather
conditions. Lightweight, low slope roof
structures, such as “big box” stores, warehouses,
distribution centers, and shopping malls are often
plagued by snow-induced loading concerns.
Although the potential for collapse is not solely
limited to low slope systems, these lightweight
roof structures have low permissible snow load to
dead load ratios making them more susceptible to
changing snow loads.
To help alleviate current economic and budgetary
constraints, the American Society of Civil
Engineers recommends snow channeling3. Snow
channels are used to reduce the weight of
accumulated snow on the building, promote
positive water flow, and increase the rate of
melting. Snow channels begin at a drainage
device and proceed up a slope. Channels are
created in widths equal to five feet (minimum) to
one-third of the column spacing beginning at the
mid-span between columns3. In some situations,
it may be necessary to widen the channels to
accommodate additional snow load reduction.
MANAGING SNOW LOADS
Although the weight of snow can vary
dramatically from storm to storm, an ordinary
solid square foot of ice weighs approximately
62lbs. As a result, increasing ice and snow
accumulation can lead to potential structural
loading concerns including full or partial roof
collapses.
CONCLUSION
Winter weather poses many hazards to facility
managers including partial or complete structural
collapses, roof leaks, snow drifts, and icicle
formation. Promoting positive drainage is an
important consideration in preventing structural
collapse and moisture infiltration during winter
weather events. Snow channeling is used to
reduce the weight of accumulated snow on the
building and promote positive water flow. Since
it is not necessary to remove all the snow and ice
from the roof, snow channeling is an economical
method for promoting positive water flow and
mitigating structural concerns during the winter.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
City
2013/2014 Snowfall
Erie, PA
137”
Syracuse, NY
131”
Buffalo, NY
128”
Grand Rapids, MI
114”
Rochester, NY
112”
Billings, MT
100”
Ann Arbor, MI
92”
Detroit, MI
91”
Toledo, OH
85”
Cleveland, OH
84”
Table 2. Top 10 Snowiest US Cities2
1.
2.
3.
Once atmospheric conditions begin to improve,
snow and ice will begin to thaw or evaporate.
However, if the drainage system is blocked by
snow and ice, the weight of snow and snow
meltwater will not significantly diminish.
Therefore, for any snow and ice removal plan to
be effective, the roof must be cleared to promote
positive drainage. However, the complete
removal of snow from a roof structure,
particularly a large building, is costly and time
consuming. Additionally, in some situations, the
complete removal of snow from the roof system
may induce greater stress on the roof structure.
© 2014 Low-Slope Solutions
2013-2014 Northeast and Midwest Winter Stats
Fenner, J. (2014) The endless winter. Snow Magazine
25-35.
Dolhon, A. M. & Ratakonda, R. (2011). Snow removal
strategies of lightweight, flat roof structures. Structure
Congress, 1782-1793.
Provided by Low-Slope Solutions
888.764.6968
[email protected]
www.lowslopesolutions.com
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On Thin Ice 2