Mid-Atlantic Region Sweeps Skylights Clear
to Prevent Further Storm Problems
February 19, 2010
East Coast residents will go into the snowstorms forecasted for
early next week with a number of lessons learned from last weeks
record-breaking snow, including the importance of removing snow
from skylights. In many cases, problems such as the one faced at
the start of the storm by the Richmond, Va., City Hall (CLICK
HERE for related story) can be prevented if the necessary steps
to remove snow and ice are taken.
Building owners and maintenance engineers need to be aware
of the design loads of the skylights and sloped glazing and take
the precautions and actions for removal, says industry consultant
Greg Carney, president of C.G. Carney and Associates Inc., who describes
a condition known ice damming.
Additional load and safety concerns are created when theres
ice on a roof or other sloped surface. The process of the snow and
ice thawing during the day and refreezing as temperatures drop during
evening hours results in what is commonly called ice damning,
explains Carney. Ice damning is a concern for both commercial
and residential roofs, skylights and sloped glazing as the condition
can lead to water penetration as well as structural damage or failure.
So its an issue of load factors, but also of retaining ice
According to Chuck Anderson, codes and industry affairs manager,
for the American Architectural Manufacturers Association, ASTM E1300
deals with the resistance of glass due to snow. He explains it does
so by rating the resistance to long duration loads (30 days); the
required design snow loads for a given geographical location come
from ASCE 7.
A lot of commercial building packages have a standard snow
load rating of 30-40-50 pounds per square foot (psf), so somehow
you have to convert the inches of snow on your roof to psf. Since
not all snow is created equal I personally know of building owners
weighing a square foot of snow on their roofs to give them a comfort
level with the integrity of the building, says Anderson. Load
resistance of a flat glass skylight could be calculated by an engineer
with all of the parameters given to him.
Anderson also says that, in theory, a Durst chart could be used
to convert the DP rating of the product to a long duration load,
but it might be overly conservative because the glass resistance
is probably a lot higher than the DP rating.
Additionally, not many skylights carry a label, so it will
be hard to identify what is in the opening, says Anderson,
who adds that its not just skylights that can be a concern.
Awnings are also at risk, as well as the main roof. A heavy
rain can really make the snow weigh a lot, and scuppers are likely
News reporters have advised East Coast residents that the cumulative
snow weighing down their roofs can lead to significant damage, such
as the Smithsonian faced when the rooftop of an offsite storage
facility collapsed last week (CLICK
HERE for related article).
And Carney adds, Given the recent weather conditions, building
owners and maintenance engineers would be wise to take the necessary
steps for removal. Also, as snow begins to melt they will also need
to take into consideration situations where ice and chunks might
fall off buildings and can cause injuries. So its a safety
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