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SUPERSTRUCTURES
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    SuperScript is a quarterly newsletter from SUPERSTRUCTURES. Founded in 1981, we are a firm of architects, structural engineers, and conservators dedicated to the art and science of exterior restoration.

      SuperScript

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      April 4, 2019

      Frost Jacking Day Tracker – Second 2018-2019 Season

      SUPERSTRUCTURES is excited to launch the second season of the Frost Jacking Day Tracker. “Frost jacking” is what happens when freezing temperatures cause rain or snow to turn to ice and expand cracks in a facade. As cycles of freezing and thawing accumulate, the cracks continue to grow and exterior hazardous conditions or interior water damage or leaks can occur. We’ll be updating the tracker every month between December and April of each season so that you can understand the effect New York City’s frost jacking cycles are having on your properties.

      March Update: This season has been very similar to last season – the exact same number of days below freezing, and just one less frost jacking day. What has been unusual has been the larger percentage of freeze-thaw days (with no precipitation in the 2 days preceding) – nearly three-quarters, much more than the typical two-thirds (the highest percentage in a decade). We’ll keep tracking through April, but this may be the final update for the season.

      What is Frost Jacking?

      In New York City, every time it rains or snows, water seeps into crevices, pores, and even micro-cracks in building facades and parapets, whether in concrete, brick and mortar, or other architectural materials. Unlike other liquids, water expands in size after it freezes. Cycles of precipitation at temperatures above freezing followed by temperatures below freezing expand the sizes of cracks, in a phenomenon known as “frost jacking,” eventually causing visible distress. This distress needs to be investigated to ensure that hazardous conditions haven’t occurred. As buildings age, these cracks can also become the source of water damage and even leaks into the interior of your building.

      Do cold winters have more frost jacking days?

      Yes. In New York City, about two-thirds of the days below freezing are freeze/thaw days, and about one-third of the days below freezing are frost-jacking days, so if there are twice as many cold days as the year before, one can expect about twice as many frost jacking days. Colder winters also start earlier, in November, while warmer winters start in December. Cold or warm, frost jacking days persist into March and even April.

      What is more important is the accumulation of those days over time. The Frost Jacking Day Tracker shows this accumulation. Facades of all buildings over six stories must be inspected every five years. That inspection should be scheduled two years before the filing due date, to allow for any required design and construction.

      What is our methodology?

      We’re using data provided to the National Weather Service by the weather station in Central Park. Since minimum and maximum temperatures are recorded at midnight, we look for days where the minimum temperature is 30 degrees F or lower preceded by days where the maximum temperature is 33 degrees F or higher, with rain and/or snow one or two days before.

      What climatologists refer to as “freeze/thaw days” can affect vegetation, soil erosion, outdoor equipment, and are a leading cause of potholes. Snowfall can actually reduce the number of effective freeze/thaw days. Vertical surfaces of buildings are different than these horizontal surfaces. Our count of frost jacking days, taking precipitation into account, is a better indicator of the causes of building distress in New York City.

      Of course, taller buildings and buildings closer to the coast will likely experience more frost jacking days. Similarly, persistent snow at a roof parapet, window ledge, or terra cotta water table may cause frost jacking as the snow melts and refreezes. For your property, consider the number as a minimum.

      The “last inspection/repair” might be the critical examination date for a building subject to FISP requirements, or the date of completion of a facade repair campaign. If this occurred between October and April, the number of frost jacking days may decrease. The cumulative number of frost jacking days isn’t a precise indicator of facade behavior: there are other variables, such as age, condition, orientation, materials of construction, etc. But it may help you understand why your building may be experiencing new problems and why it needs to be periodically inspected.

      You can view the data from the inaugural 2017-2018 season by clicking here.

       

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