Sumner County inspectors review slab and footing standards, urge Ufer grounding on new builds

Sumner County inspectors walked board members through common problems with monolithic slabs, footings and grounding on April 16, urging clearer permit requirements and at least one dedicated inspection for slab grounding on new residential builds.

The discussion centered on construction details that inspectors said are still frequently installed incorrectly. "It's a good, useful guide to look at when you're looking at a slab, footing for a foundation," said Terry, a staff member, describing a 2015-era checklist the office uses when inspecting slabs and footings. He ran through minimum splice and embedment requirements, vapor-barrier and gravel specifications, anchor-bolt spacing, and insulation around slab edges.

Why it matters: inspectors said improper footings or poor grounding can lead to structural failures and safety hazards. The panel debated how to ensure a durable electrical ground for slabs — the so-called Ufer ground — is provided and inspected before concrete is poured.

Terry told the board that the department follows guidance adopted with the 2015 code cycle and that several items are now required that were not in earlier editions. "Whenever this was drawn, we didn't have grade stops. They weren't required, and they are now," he said, explaining grade stops help set slab elevation during pours. He also listed recurring field failures: insufficient rebar splice/turns at corners, inadequate compacted gravel under slabs, missing 10-mil vapor barrier documentation, and anchor bolts spaced incorrectly. "Top of the footing must be level and any loose dirt must be removed from the bottom and the footing must have 12 inches below the finish grade," Terry said.

On grounding, staff described field experience with concrete-encased electrode practices and recommended avoiding bare copper embedded in concrete because of corrosion in high-pH concrete. "When they first started doing it, they would take a copper... and they'd run 20 or 30 feet down and let it just go in and out... they found out that the copper, the pH in that concrete was eating the copper up," Terry said, describing a shift toward galvanized steel ground rods and tying the ground into rebar that is then bonded to the service grounding conductor above slab level.

He recounted a case in which a footing that held moisture was damaged after being struck by lightning and said that concrete-encased electrodes (Ufer grounds) can provide a stable impedance if installed correctly. "I would put it on your permit application," Terry said, urging the board to add a Ufer-ground line item to the permit so it will be visible to builders and trigger inspection.

Staff repeatedly emphasized that many of the slab checks must occur before plumbers cover rough-in work or before plastic and wire mesh are placed. Terry noted common checklist points: rebar splices and bulkheads of at least 16 inches, two rows of #4 rebar where required, a 10-mil vapor barrier, maximum 2-inch aggregate for compacted base, minimum 4 inches of compacted gravel under the slab, and anchor bolts no more than 6 feet apart and within 6 inches of corners and splices.

Department staff also described differences on commercial projects, where structural engineers often specify greater reinforcement and footing details to match heavier loads, and said the office is working to add capacity to perform an additional inspection if required. "We're working on our staff right now to where we can cover another inspection or two," a staff member said, adding the department had recently hired Eduardo, "our newest licensed inspector."

The board discussed enforcement language and inspectors said they typically accept rebar chairs and bonded rebar in place of embedded copper conductors. Staff recommended specifying the Ufer (concrete-encased electrode) requirement on permit applications and inspection checklists and showed photographs from recent field inspections to illustrate compliance and noncompliance.

Votes at a glance: The meeting recorded routine procedural votes by voice vote; no recorded roll-call tallies were provided in the transcript. The board approved minutes from 01/15/2022, approved the meeting agenda, and later approved adjournment. All three actions were described as carried by voice vote; exact counts were not specified.

The board did not take regulatory action at the meeting but staff indicated they will pursue an administrative change to permit applications and inspection procedures to require documentation or visible provision of a concrete-encased grounding electrode before slab placement.