What goes under each pier, and are plastic ABS pads allowed?

Each pier needs a footing that spreads its load over enough soil. HUD's installation standards accept concrete footings (at least 4 inches thick if precast, or 6 inches if poured in place), pressure-treated wood in at least two 2-inch layers, ABS plastic footing pads if they are listed for the use, and other listed materials. Footing size comes from the load on the pier and the soil's bearing capacity, so weak soil needs bigger pads. The footing must sit on firm, undisturbed soil or compacted fill with organic material removed. In freezing climates, conventional footings must go below the local frost line. Follow the home's installation instructions or a design approved by your building department.

Check your local rule. This varies by state, county or city. Your permitting office has the final word; the official lookup pages below show you who that is.

Sources

• 24 CFR Part 3285, Model Manufactured Home Installation Standards (2020 edition)U.S. Government Publishing Office (HUD regulation)