When do I need an engineer for a small home foundation?

You need one whenever the soil or the design falls outside simple prescriptive rules, and some Texas cities require one for every foundation. HUD's installation standards call for a registered engineer, architect or geologist when soil looks like peat, organic clay or uncompacted fill, and for block piers taller than 67 inches. Texas anchoring rules require engineer design when the roof pitch is over 20 degrees, and in Wind Zone II when tie spacing exceeds 8 feet on center. Texas TB 10-01 says foundations on expansive soils must be designed under IBC section 1808.6. North Central Texas regional IRC amendments, adopted by many DFW-area cities, require every foundation to be designed and sealed by a Texas-registered engineer. Ask your building office early.

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)
• 10 Tex. Admin. Code 80.24, Generic Standards for Anchoring SystemsLegal Information Institute, Cornell Law School (Texas regulation text)
• 2021 IRC Regional AmendmentsNorth Central Texas Council of Governments