What are the rules for concrete block piers under a manufactured-style home?

HUD's installation standards give a recipe. Blocks must be at least 8 by 8 by 16 inches nominal, laid with hollow cells vertical, topped with a solid cap at least 4 inches thick (or hardwood at least 2 inches nominal), and shimmed with hardwood wedges used in pairs. Single-stack block piers may be up to 36 inches tall; double-stacked piers may reach 67 inches; anything taller needs an engineer or architect. Frame piers go no more than 24 inches from each end and no more than 120 inches apart center to center, with closer spacing set by soil and load tables. FEMA notes unreinforced dry-stacked blocks have failed in floods and strong winds, so reinforced piers are preferred in hazard areas.

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)
• FEMA P-85, Protecting Manufactured Homes from Floods and Other HazardsFEMA