Footings shall be placed a minimum of 24 inches
below grade in undisturbed soil (see Figure 3-2). For exceptions see §
156-13B(2) and
(3). Support every pier with a properly designed footing [see Subsection A(1), below].
A. Acceptable types of footings.
(1) Concrete. Footings may consist of precast or poured-in-place
concrete, pads, slabs or ribbons at least 3 1/2 inches thick,
with a twenty-eight-day compressive strength of at least 3,000 pounds
per square inch.
(2) Pressure-treated permanent wood. Two layers of nominal
two-inch thick pressure-treated wood having 0.60 retention in accordance
with AWPA C22 Standard, with the long dimensions of the second layer
placed perpendicular to that of the first, may also be used.
(3) Other materials. Other materials approved for footings
may be used when approved by Kent County if they provide equal load-bearing
capacity and resistance to decay. Examples include:
(a)
One-half-inch maximum crushed stone.
(b)
Three-eighths-inch or three-fourths-inch graduated
gravel.
(c)
Coarse sand, with grains no smaller than one-sixteenth-inch,
placed so it provides a soil-bearing capacity of at least 3,000 pounds
per square foot.
B. Frost protection.
(1) Conventional footings. Place footings 24 inches below grade (see Figure 3-2). For exceptions see Subsection
B(2) and
(3).
(2) Floating slab systems. When properly designed by a registered professional engineer, a floating slab system may be used above the frost line. The design shall accommodate the anchorage requirements identified in Article
V.
(3) Insulated foundations. Footings may also be placed
above the frost line when the home is provided with a perimeter foundation
or skirting having insulation properties sufficient to prevent freezing
of the soil under or adjacent to every load-bearing component of the
foundation and acceptable for this purpose to Kent County. Useful
design guidelines may be found in the references found in Appendix
A. Insulation systems should be compatible with the requirement
to cross-ventilate the entire space under the home.
C. Proper sizing of footings. Proper sizing of footings
depends upon the load-carrying capacity of both piers and the soil.
See Table 4-3 for recommended footing sizes.