24 CFR §3285.304

1. (a)Concrete blocks. Installation instructions for concrete block piers must be developed in accordance with the following provisions and must be consistent with Figures A and B to § 3285.306.
   1. (1)Load-bearing (not decorative) concrete blocks must have nominal dimensions of at least 8 inches × 8 inches × 16 inches;
   2. (2)The concrete blocks must be stacked with their hollow cells aligned vertically; and
   3. (3)When piers are constructed of blocks stacked side-by-side, each layer must be at right angles to the preceding one, as shown in Figure B to § 3285.306.
2. (b)Caps.
   1. (1)Structural loads must be evenly distributed across capped-hollow block piers, as shown in Figures A and B to § 3285.306.
   2. (2)Caps must be solid concrete or masonry at least 4 inches in nominal thickness, or hardboard lumber at least 2 inches nominal in thickness; or be corrosion-protected minimum one-half inch thick steel; or be of other listed materials.
   3. (3)All caps must be of the same length and width as the piers on which they rest.
   4. (4)When split caps are used on double-stacked blocks, the caps must be installed with the long dimension across the joint in the blocks below.
3. (c)Gaps. Any gaps that occur during installation between the bottom of the main chassis beam and foundation support system must be filled by:
   1. (1)Nominal 4 inch × 6 inch × 1 inch shims to level the home and fill any gaps between the base of the main chassis beam and the top of the pier cap;
   2. (2)Shims must be used in pairs, as shown in Figures A and B to § 3285.306, and must be driven in tightly so that they do not occupy more than one inch of vertical height; and
   3. (3)Hardwood plates no thicker than 2 inches nominal in thickness or 2 inch or 4 inch nominal concrete block must be used to fill in any remaining vertical gaps.
4. (d)Manufactured pier heights. Manufactured pier heights must be selected so that the adjustable risers do not extend more than 2 inches when finally positioned.