NOTE: This article only covers foundations. Installation procedures and methods for securing the home to its foundations are discussed in Article V.
A. 
Importance. Proper pier installation is the most important part of home installation. Incorrect size, location or spacing of piers may cause serious structural damage to the home. It is important to install piers around the perimeter as required. Failure to do so may lead to sagging floors, walls and roofs [see § 156-12E(3)].
B. 
Acceptable types. Piers may be concrete blocks, pressure-treated wood having 0.60 retention in accordance with American Wood Preservers Association (AWPA) C22 Standard or adjustable metal or concrete piers (see Figure 4-1[1]). Manufactured piers shall be listed or labeled for the required load capacity.
[1]
Editor's Note: Figure 4-1 is included at the end of this chapter.
C. 
Design requirements.
(1) 
Load-bearing capacity. The load that each pier must carry depends on such factors as the dimensions of the home, the roof live load, the spacing of the piers and the way the piers are used to support the home. Center beam/marriage wall blocking is required for multisection homes. See Tables 4-1 and 4-2 for pier capacities.[2] The tables shall be used when the manufacturer's installation instructions are not available. Manufactured piers must be rated at least to these capacities, and locally constructed piers must be designed to transmit these loads safely [see Subsection C(2), below].
[2]
Editor's Note: Tables 4-1 and 4-2 are included at the end of this chapter.
(2) 
Configuration.
(a) 
Figure 4-1 shows the recommended arrangement of concrete block piers constructed on site. Load-bearing (not decorative) concrete blocks should have dimensions of at least eight inches by eight inches by 16 inches. They must be stacked with their hollow cells aligned vertically. When piers are constructed of blocks stacked side by side, each layer should be at right angles to the previous one (see Figure 4-1[3]).
[3]
Editor's Note: Figure 4-1 is included at the end of this chapter.
(b) 
Cap hollow block piers as shown in Figure 4-1 to distribute the structural load evenly across them. Caps may be of solid masonry of at least four inches nominal thickness or hardwood at least two inches nominal thickness or of steel (see Figure 4-1). All caps shall be of the same length and width as the piers upon which they rest. Avoid using plywood, as it may lead to unwanted settling.
(c) 
Use four-inch by six-inch hardwood shims to level the home and fill any gaps between the base of the I-beam and the top of the pier cap. Always use shims in pairs (see Figure 4-1). Drive them in tightly so that they do not occupy more than one inch of vertical space. Use hardwood plates no thicker than two inches to fill in any remaining vertical gaps.
(d) 
Select manufactured pier heights so that the adjustable risers do not extend more than three inches when finally positioned.
(e) 
All piers must rest on footings (see § 156-13) that extend below the frost line (see § 156-13B for exceptions to placement) and are placed on either undisturbed soil or compacted fill.
(3) 
Clearance under homes. A minimum clearance of 12 inches shall be maintained beneath the lowest member of the main frame (I-beam or channel beam) in the area of utility connections. No more than 25% of the lowest member of the main frame of the home shall be less than 12 inches above grade.
D. 
Design procedures.
(1) 
Piers less than 36 inches high. Piers less than 36 inches high may be constructed of single, open or closed-cell concrete blocks, eight inches by eight inches by 16 inches. Install them so that the long sides are at right angles to the supported I-beam (see Figure 4-1). Position open cells at right angles to the footers. Horizontal offsets should not exceed 1/2 inch top to bottom. Mortar will not normally be required. Manufactured piers should be listed and labeled.
(2) 
Piers 36 inches to 80 inches high and corner piers. Construct all piers between 36 inches and 80 inches high and all corner piers over three blocks high out of double, interlocked concrete blocks (see Figure 4-1). Mortar will not normally be required.
(3) 
Piers over 80 inches high. Where permitted by Kent County, lay blocks in concrete mortar with steel reinforcing bars inserted in the block cells and fill the cells with concrete (see Figure 4-1). Where such construction is not permitted by Kent County, due to other conditions, piers over 80 inches high shall be designed by a registered engineer.
(4) 
Elevated homes. When more than 1/4 of the area of a home is installed so that the bottom of the mainframe members are more than three feet above ground level, the home stabilizing devices shall be designed by a qualified engineer and be approved prior to installation by Kent County.
E. 
Location and spacing. The location and spacing of piers depend upon the dimensions and width of the home, the roof load zone, the type of construction (single or multisection) and such other factors as the location of doors or other openings. In general, locate piers no more than two feet from either end and not more than eight feet center-to-center under the main rails.
(1) 
Single-section homes. Figure 4-2[4] shows the recommended location and spacing of piers for a single-section home when the manufacturer's installation instructions are not available.
[4]
Editor's Note: Figure 4-2 is included at the end of this chapter.
(2) 
Multisection homes. Figure 4-3[5] shows the recommended location and spacing of piers for a multisection home when the manufacturer's installation instructions are not available.
[5]
Editor's Note: Figure 4-3 is included at the end of this chapter.
(3) 
Perimeter blocking. Place piers on both sides of side wall exterior doors and any side wall door openings greater than four feet (such as entry and sliding glass doors). Piers are also recommended under those locations where heavy pieces of furniture, such as pianos, organs, waterbeds, etc., are expected to be placed.
Footings shall be placed a minimum of 24 inches below grade in undisturbed soil (see Figure 3-2[1]). 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.[2] Insulation systems should be compatible with the requirement to cross-ventilate the entire space under the home.
[2]
Editor's Note: Appendix A is included at the end of this chapter.
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[3] for recommended footing sizes.
[3]
Editor's Note: Table 4-3 is included at the end of this chapter.
[1]
Editor's Note: Figure 3-2 is included at the end of this chapter.
A. 
Kent County guidelines for the installation of manufactured homes on permanent foundations include the following requirements:
(1) 
Is supported on a properly designed and constructed foundation system that is adequate to support all loads and as specified in this chapter.
(2) 
Is anchored adequately to resist all loads and as specified in this chapter.
(3) 
The towing hitch and all running gear have been removed.
(4) 
There is a properly enclosed crawl space or basement with permanent foundation-type construction.
B. 
Useful ideas and design guidelines can also be found in reference publication, such as those listed in Appendix A.[1]
[1]
Editor's Note: Appendix A is included at the end of this chapter.
Also see § 156-17C.
A. 
Areas prone to flooding.
(1) 
Special elevations and anchoring techniques are required when locating a home in an area prone to flooding.
(2) 
Installations in flood zones other than velocity ("V") zones may be installed using piers as shown in Figure 4-4.[1] Other installation designs and all installations in a V zone must be designed by a registered design professional to make sure that the home design and construction conform to applicable federal, state and local codes and regulations, and that the foundation system will adequately support the loads imposed in a flood situation. The Federal Emergency Management Agency (FEMA) publication listed in Appendix A contains design and construction recommendations for elevated foundations as well as for connections and anchoring systems that will allow the foundation system to resist flood forces.
[1]
Editor's Note: Figure 4-4 is included at the end of this chapter.