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Your Roof In Winter: Understanding The Effects Of Cold Weather

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As terms like "polar vortex" and "glacial melting" become more commonplace, maintaining the roof over your head is more crucial than ever.  It's important to realize, though, that every roof may not be constructed to withstand these changing, unpredictable weather patterns.  Most roofs come with a 20-year warranty, and they're typically designed to last at least that long: but they probably weren't constructed to withstand the drastic, devastating weather conditions that could occur when Antarctica melts into the sea!  During erratic wintry weather, there are four culprits that can weaken your roof and shorten its longevity:

1.  Gravity Load:  Simply put, the gravity load is the weight of the accumulated snow on your roof.  More specifically, it's the force vector of the snow's weight as the pull of gravity causes it to slide down the roof's slant.  Bear these figures in mind:

  • 1 cubic foot of dry snow weighs 6-8 lbs/ 3-4 kg
  • 1 cubic foot of packed snow can weigh up to 20 lbs/ 9 kg
  • 1 cubic foot of ice can weigh 50-60 lbs/ 22-27 kg

That weight can add up fast.  Additionally, flat, industrial roofs have higher gravity loads than their pitched counterparts, which are typically used in home construction.  Calculating gravity load--and your roof's maximum capacity for it--involves some tricky trigonometry.  So, check out this snow load calculator and let your computer do the work for you!

2.  Ambient Thaw:  No math to it--the ambient temperature is simply the air temperature at your roof's level.  It determines the rate that the snow melts and slides off its surface.  As the daytime temperature rises, some of the snow begins to melt; in the chilly night air, however, it can re-freeze into a much denser precipitate--or even heavy ice.  This is a normal part of the freeze-thaw cycle, but it causes your roof to be burdened by a dynamic, ever-changing mass.

3.  Solar Thaw:  Particularly on darker-colored roofs, some sunlight may penetrate the snow and be absorbed by the roof's surface beneath it.  This causes the surface temperature to rise, which may provoke a sudden roof-top avalanche. (Multi-level roofs are especially affected by solar thaw: snow may melt on one level and simply slide off onto the one below it, exponentially increasing its weight and, subsequently, its gravity load.)  Though your roof is relieved of the snow's weight, the force of it being pulled off by gravity is not insignificant. 

4.  Heat Loss Thaw:  This part of the thaw-freeze cycle is caused by heat energy emitted through the roof of your house, which, in turn, can cause thawing and re-freezing of the snow piled on top of it.  Energy and environmental standards have changed a lot over the last 10--even five--years.  Generally, less heat escapes from the roof of newer homes--older constructions may, for instance, require additional insulation to make them more energy efficient.

Mild amounts of snow accumulation can act as an extra layer of insulation, trapping more heat inside your house.  Understanding gravity loads and the thaw-freeze cycle can help you to better gauge your roof's condition--especially as the climate continues to fluctuate wildly.  Inspect your roof with these concepts in mind after every wintry storm.  Talk to professionals like Rippy's Roofing & Construction Inc today.