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Buckling of Snow
When the blanket of snow on the roof is dense and wet (not solidified), it may tend to undergo compression buckling, pushing a “loop” upward from the roof surface as the heavy mass compresses toward the eave where restrained by snow guards. This loop, can fold over the blanket and the snow retention device(s) in the downslope direction, often breaking and in many cases falls from the roof.  This tends to happen more when blankets are thin, as when the thickness of the blanket increases- it gains compressive strength.  This tendency is related to both the vector force (and mass) and the compressive strength of the snow.  Hence the following variables are at play:
  1. Slope- more common with steeper slopes as vector forces increase
  2. Thickness of snow blanket- thicker blankets generally have greater compressive strength and lower mass, therefore less likely to buckle
  3. Moisture- greater moisture content increases mass (greater probability)
  4. Temperature- warmer temperatures decrease compressive strength, therefore increasing buckling probability
  5. Length of blanket- longer blankets increase vector and probability of buckling
Contrary to popular myths, height of the snow retention device plays no role in the probability of a snow blanket to buckle, and heavier accumulations decrease probability, not increase it.


Commentary- solution

This is analogous to compression buckling of a steel column, except that the properties of the snow are less predictable.  The problem is noted when snow blanket is minimal in thickness and very wet (lacking in body and compressive strength).  Two solutions:
  1. reduce the unsupported length of the column (snow blanket), and
  2. increase the sectional size of the column (snow blanket).  The first is accomplished by adding rows of snow retention.  The second we have no control over, but it is actually a good thing; when the snow blanket increases in depth, it is less likely to buckle.
When adding rows of snow retention it is our experience the most effective approach is to add a second row some 8-10’ more or less above the first.  If the blanket buckles above the upper row, the “loop” is usually still contained above the lower row.