The reason I believe this hasn't be an issue yet is its so rare to build full foundations under porches.
I would add that in the Willamette Valley of western Oregon (Eugene, Roseburg, Salem, and upwards to Portland) although the frost line is only a few inches, they still very often put in a footer and stem wall when building a porch. Seems like this method is common enough in different parts of the country that CA (and Home Designer (Pro which I'm using) should be fixed/improved to incorporate some foundation options for porches instead of almost tying our hands.
Porches and foundations
in General Q & A
Posted
I would add that in the Willamette Valley of western Oregon (Eugene, Roseburg, Salem, and upwards to Portland) although the frost line is only a few inches, they still very often put in a footer and stem wall when building a porch. Seems like this method is common enough in different parts of the country that CA (and Home Designer (Pro which I'm using) should be fixed/improved to incorporate some foundation options for porches instead of almost tying our hands.