Frost

Recent data from the University of New Hampshire has challenged the conventional wisdom that the depth of the recharge bed should exceed the depth of frost penetration in the local area. At UNH, the frost depth is 48 inches. While the porous pavement at the site extends to below the frost depth, their data from 2006 shows frost penetration in the recharge bed of less than one foot, or less than 25 percent of the frost penetration. Based on their research, the University conservatively recommends the depth of the bed be 65 percent of the frost depth in their design specifications.

Other porous pavements have been installed in freezing climates with total depths much shallower than the frost depth in their respective regions. These include pathways at Swarthmore College (Pennsylvania) at a depth of 12 inches and a Walden Pond Visitor Center (Massachusetts) parking lot with a bed depth of 12 inches. None of these pavements have shown damage due to frost heave.