Why did an engineer pick helical piers for a Tulsa crawl space home?

Reviewed by Preston, Oklahoma foundation repair consultant · Updated 2026-10-14

east Tulsa20261-story house with converted garage, brick veneer and vinyl sidingPier-and-beam crawl space; perimeter continuous footing with clay tile stem wall (assumed)

In short: An east Tulsa crawl space home with a converted garage showed veneer separations over 1/2 in. and out-of-square doors despite earlier, undocumented underpinning. The engineer presumed moisture-reactive clay and missing gutters as the cause and specified 10 exterior helical piers at least 20 ft below grade, shimming of crawl supports, and drainage maintenance ¹.

What did the house show?

• Brick veneer separations over 1/2 in. on the north side, and veneer-to-trim gaps over 1/4 in. at the northwest and southwest corners ¹.
• The south door of the converted garage out of square, and interior drywall cracks ¹.
• Previous underpinning along the north, west and south sides, with no documentation available ¹.
• A mostly dry crawl space, loose floor supports in the south crawl, and added braces in the north crawl that the engineer judged were for floor vibration only; the 2x8 joists at 16 in. on center were adequate ¹.
• Incomplete guttering and cracked exterior flatwork, which the engineer rated non-structural ¹.

What did the engineer find was causing it?

With no geotechnical data, the engineer presumed moisture-reactive clay whose shrink-swell causes loss of support and uplift at the perimeter footing. The incomplete gutter system contributed; possible fill or slope issues were noted as beyond the report's scope. The engineer's stated aim was to carry the footing down to soil "less affected by climate, soil conditions and/or homeowner's actions" ¹.

What repair was specified?

• 10 exterior piers under the perimeter footings. Helical piers were specifically recommended because of the clay tile stem wall and the light weight of the garage. Drilled concrete piers with a bell at least twice the shaft diameter, or drilled steel piers, were also acceptable ¹.
• Minimum depth 20 ft below existing grade, bearing on a stronger stratum such as bedrock or weathered shale, unless the engineer approved otherwise ¹.
• Jack the footings after piering, and notify the engineer if jacking was not possible ¹.
• Verify the garage footing during installation; expose existing piers in at least 3 places (up to 10 ft deep) and call the engineer if a pier-and-grade-beam foundation was found ¹.
• Level and tight-shim all crawl space girders and supports; rebuild or re-side the northwest veneer ¹.
• Plumbing tests of supply and sewer lines after piering, and suggested before ¹.
• Gutters; downspout and condensate extensions 36 to 48 in. from the foundation; grade sloped 2 to 5 percent away; low spots filled with sandy clay; no sprinkler use in wet weather ¹.
• Engineer inspection before backfill (24-hour notice) if certification was wanted; any pier relocation needed the engineer's approval ¹.

What does this case show about Oklahoma foundations?

The project record lists the Coweta series mapped at the site ¹. USDA describes Coweta as a shallow, well-drained soil formed from soft Pennsylvanian sandstone interbedded with shale, with the soft rock typically about 15 in. down and harder sandstone at 2 to 5 ft in some places ². That is far shallower than the engineer's 20 ft default, and the spec's engineer-approval clause is how a shallower refusal on rock gets accepted ¹.

The pier choice turned on the structure, not just the soil. A push pier is driven using the building's own weight as reaction, so a light garage and a fragile clay tile stem wall led the engineer to helical piers ¹.

The drainage advice is close to published guidance. The engineer asked for 36 to 48 in. extensions and 2 to 5 percent grade ¹; federal building-science guidance recommends at least 5 ft of discharge distance and at least 1/2 in. per foot of fall for 10 ft ³.

Related

• Helical Piers
• Steel Push Piers
• Pier and Beam Crawl Space
• Working with Engineers
• Soil - Coweta
• Pier Uplift or Movement After Repair