15 AUGUST 2005
Design Depth of Ordinary Frost Penetration. For average permanent
structures, the depth of frost penetration assumed for design in situations not affected
by heat from a structure, should be that which will occur in the coldest year in 30 years.
For a structure of a temporary nature or otherwise tolerant of some foundation
movement, the depth of frost penetration in the coldest year in 10 years or even that in
the mean winter may be used, as may be most applicable. The design depth should
preferably be based on actual measurements or on computations if measurements are
not available. When measurements are available, they will almost always need to be
adjusted by computations to the equivalent of the freezing index selected as the basis
for design, as measurements will seldom be available for a winter having a severity
equivalent to that value.