Pier and Beam Crawl-Space Underpinning Sequence

Why this matters

Pier and beam houses with masonry perimeter crawl walls fail differently than slab homes. The interior wood piers, the perimeter stem wall, and the wood girders all settle at different rates and in different directions, and the floor framing telegraphs every bit of it. Underpinning a crawl-space structure without sequencing the lift, the temporary support, and the wood-to-pier connection produces a foundation that is well piered and a floor that is still bouncy and out of level. This article walks the production sequence that produces a lifted, level, and tight pier and beam underpin.

Pre-job survey

Pull elevations on every interior wood pier top and at every girder bay using a rotary laser (Topcon RL-H5A or Spectra LL300N) and a millimeter receiver, or with an optical level if a clear sight line is available. Map the readings to a crawl-space floor plan. Note girder spans, joist spans, double-joist locations, and the locations of mechanical chases.

Probe the soil under every wood pier with a Dynamic Cone Penetrometer (DCP, ASTM D6951) to identify which piers are sitting on competent bearing and which are sitting on disturbed fill or organic topsoil. A pier with DCP penetration over 4 inches per blow at 12 inches of depth is on weak bearing and is a candidate for replacement, not just lift.

Photograph the existing condition top to bottom: perimeter stem wall both sides, every wood pier, every girder bearing, the underside of the subfloor, and any plumbing or HVAC chases that will interfere with shoring.

Temporary shoring

Before any permanent pier sees load, the structure has to be supported on temporary shoring that bypasses the existing wood piers and stem wall. Standard temporary shoring stack from the bottom up:

• 24 inch by 24 inch by 4 inch concrete cribbing pad or 6 inch by 6 inch by 24 inch hardwood mud sill on undisturbed soil
• 6 inch by 6 inch by 12 inch hardwood blocking, stacked to within 4 inches of the girder underside
• 20-ton bottle jack or 25-ton screw jack
• 6 inch by 6 inch by length-as-needed hardwood post to the girder
• 6 inch by 6 inch by 24 inch hardwood saddle blocking under the girder

Set shoring at every other joist bay perpendicular to the girder run, with no shoring point spaced more than 6 feet from the next. Shore both sides of every girder splice. Take up the slack on every jack so the structure is held but not yet lifted.

Lift sequence

Lift in 1/8 inch increments, walking the shoring line end to end, taking up each jack a notch and then the next, never lifting one point ahead of its neighbors by more than 1/4 inch. The slow walk-through prevents the structure from racking and cracking interior plaster, drywall, and tile.

Stop lifting at the point where doors swing freely, finish floors return to level within 1/2 inch over 20 feet, and exterior brick veneer cracks close to hairline. Past that point lift recovery turns into cosmetic damage upstairs. Document the final lift at every benchmark.

Permanent pier installation

With the structure held on shoring, install permanent piers per the engineered pier plan. For pier and beam, helical piers (CHANCE SS5 or SS150, Earth Contact Products ECP288, or Magnum MH150) are the typical residential choice because they install with a hydraulic torque motor in the limited headroom of a crawl space. Push piers work but require reaction load from the structure, which is reduced once the lift is on shoring.

Drive helicals to the engineered torque (typically 3,500 to 5,500 ft-lbs for residential at the design depth). Cut the shaft to elevation 2 inches below the girder underside.

For new interior wood piers replacing failed originals, set a 24 inch by 24 inch by 8 inch concrete pad on undisturbed soil at minimum 30 inches below grade, dry-stack CMU or pour a concrete pier to within 6 inches of the girder, and cap with a pressure-treated 6 inch by 6 inch post and a Simpson PC66 post cap.

Load transfer to the new piers

This is the step crews skip and the one that decides whether the floor stays tight. The new piers must engage the girder uniformly. Drop steel shim plates (1/8 inch to 1/2 inch ASTM A36 plate) between the pier cap and the girder until all jacks are unloaded and the load is on the piers. Test the transfer by tapping each jack handle with a steel rod: a properly transferred load makes the jack handle ring; an unloaded jack thuds.

For helical piers, the load transfer bracket (CHANCE C150-0291, ECP RPB, or Magnum MTP) bolts to the girder underside and clamps the pier shaft. Torque the through-bolts to the bracket manufacturer's spec (typically 75 to 110 ft-lbs).

Crawl space remediation around the work

Underpinning churns a crawl space. Before crew demob:

• Re-install vapor barrier (6 mil polyethylene minimum, 10 mil for IECC 2024 compliance in conditioned crawls) across the entire floor with 6 inch laps sealed with crawl-space-rated seam tape (Stego CrawlSeal or equivalent)
• Verify the perimeter foundation drain (if present) was not damaged during excavation; repair or replace as needed
• Re-attach any plumbing strapping, HVAC duct hangers, or electrical zip ties that were cut for access
• Pump out any standing water and verify the sump pump operates
• Document final condition with photos that match the pre-job inventory

References

• IRC R408 Under-Floor Space, R401 through R404 Foundations (2024 edition)
• CHANCE Helical Pier Foundation Design Manual (current edition)
• Earth Contact Products Helical Pier and Bracket Engineering Manual (2024 release)
• Simpson Strong-Tie Wood Construction Connectors Catalog C-2024
• ASTM D6951 Standard Test Method for Use of the Dynamic Cone Penetrometer in Shallow Pavement Applications
• OSHA 29 CFR 1910.146 Permit-Required Confined Spaces
• IECC R402.2.10 Crawl Space Walls (2024 edition) for vapor retarder requirements