The Footing That Heaved the First Winter

Why this matters

A footing set above the frost line looks perfect for nine months. It passes the final inspection, the customer pays, and the crew forgets the job. Then the ground freezes below the bottom of the concrete, ice forms under it, and the post on top rises a fraction of an inch at a time while the house beside it, sitting on a deep foundation, does not move at all. This case was solved backwards from the job file after the damage was done. What makes it worth reading is that every fact needed to prevent it was public and one phone call away, and the shop's own records showed the exact moment the wrong number got in.

The call in February

A handyman and small-remodel shop had built a gable porch roof over a front entry the previous June: two 6x6 posts on concrete pier footings, a ledger lagged to the house band, and a new concrete stoop pad between the posts. In February the homeowner sent three photos. The front door was rubbing at the head, the step flashing where the porch roof met the siding had pulled open along about 3 ft, and the stoop pad had a visible tilt toward the east post.

The owner went out with a level and a tape. Against the reference line the crew had snapped on the siding at the ledger height, the east post had risen 1 1/8 in and the west post 5/8 in. The ledger on the house had not moved. So the porch roof had rotated upward at its outer edge, the ledger connection was taking the bending, and the flashing had torn where the roof plane pulled away from the wall. The east corner of the stoop pad sat 3/4 in high.

The pattern alone pointed at frost: two footings rising by different amounts, mid-winter, against a structure on a deeper foundation that stayed put. A settling footing goes down, not up. A rotting post shortens. Nothing but frozen ground lifts concrete.

What the job file said

The owner pulled every record the shop had on the job before calling anyone, because the first question the homeowner would ask was whether the work had been done right, and the answer had to come from paper rather than from memory.

JOB 2214  porch roof, entry   (record excerpt)
permit app 05/20  drawing note: "pier ftgs below
                  frost, 12 in dia, sono tube"
inspections  footing  req 06/10 14:05
                      CANCELLED 06/11 07:40
                      "concrete scheduled"
             final    06/24  APPROVED
crew log 06/11  "2 piers dug 36 in, poured 9:30,
                 stoop pad formed"
photos 06/11  east hole w/ tape at 36 in
              (no photo of west hole)

Read it in order and the failure is visible. The permit drawing said "below frost" without a number, so the drawing passed plan review and committed the crew to nothing measurable. The footing inspection was requested, then cancelled the next morning because the concrete truck was already booked, and the crew poured an hour and fifty minutes later. The final inspector could only see posts, a roof and a pad. Nobody from the department ever saw a hole.

The crew log gave the depth: 36 in. That figure was not careless. It was the frost line depth in the shop's home county, where the crew had set every pier for eight years and had never had a callback. The porch was in the next county, 11 miles from the shop, across a county line the crew did not think of as a boundary.

The number that should have been read

The job's county published its climatic and geographic design criteria, the filled-in version of IRC Table R301.2(1) in the 2018 and 2021 editions as adopted locally. Its frost line depth cell read 48 in. The home county's read 36 in. Under IRC R403.1.4.1 as adopted in both counties, exterior footings extend below the frost line in that table, unless they are built as a frost-protected shallow foundation or bear on solid rock, and the exceptions for freestanding accessory structures did not apply to a roof tied into the house.

So the piers stopped 12 in short. One minute on the county's building page, or a question at the permit counter when the drawing was submitted, would have produced the number. The shop had no step that asked for it, because in eight years it had never needed one.

A note on what the 48 in actually is. The frost line depth in the table is a design value the jurisdiction sets from its climate records, measured down from finished grade. It is not a promise that frost reaches exactly that far every winter, and it is not a measured depth at this lot. In a mild winter, 36 in piers in that county may never heave. That is part of why a wrong habit survives for years.

Why the east post went further

The difference between the two posts, 1 1/8 in against 5/8 in, was worth explaining, because it told the shop how sensitive the site was and what to change in the repair.

Frost heave needs three things together: freezing temperatures reaching below the footing, a frost-susceptible soil, and a supply of water. Ice lenses grow at the freezing front by drawing water up from below, and each lens pushes the soil, and anything resting on it, upward. Silts are the most frost-susceptible soils because they hold water and pass it upward by capillary action; clean gravel is close to immune. The county soil survey and the crew's own photo showed a silty loam at this lot.

The east post had all three at their worst. It stood at the corner of the new stoop pad, which the homeowner shoveled clean all winter, and bare concrete lets frost drive deeper than ground under a snow blanket, because snow insulates. A downspout had been extended to empty within 2 ft of that corner, which kept the soil around the pier wet. The west post sat in lawn under a drift that persisted from December to March, so its frost front stayed shallower. The site, not just the depth, decided which post moved more.

There is a second mechanism worth naming. Frozen soil bonds to the sides of a pier, called adfreeze, and can lift it even when the bottom sits below frost, especially along rough concrete poured straight against the soil. Correct depth stops the lens from forming under the footing; it does not by itself stop the grip on the sides.

What the record could not tell them

The file had gaps, and the owner wrote them down as part of the finding rather than filling them with assumptions.

• No photo of the west hole. The 36 in for the west pier comes from the log alone. The excavation in April confirmed it at 35 in.
• No soil note. The silt was identified afterward from the county soil survey and the excavated material.
• No record of who cancelled the footing inspection, or why beyond the portal's two words. The office believed the crew lead had; the crew lead believed the office had.
• No depth on the drawing, which meant the plan reviewer approved a sentence rather than a number.

The repair

Nothing was dug until the ground thawed. Digging frozen silt beside a heaved footing in February would have meant breaking up frozen ground with no way to set new concrete properly. In February the shop only shored the porch roof: two adjustable steel shores on blocking under the beam, set with the roof's weight on them so the posts carried nothing more, and the torn flashing covered with a temporary membrane lapped under the siding above the tear. The shores went in with one person holding and one adjusting, never under the beam while it was being jacked, and the shores were raised only to take load, not to push the roof back down against the ledger.

By mid-April the ground had thawed and the posts had settled partway back: east post 3/8 in above the reference line, west post 1/8 in. The partial return is typical. Soil that has heaved and thawed does not come back to where it was, and the rest of the displacement stays until the footing is reset.

• Locates first. The crew filed the one-call locate request and waited the state's notice period before digging, then hand-dug within the tolerance zone of every mark, because the gas service ran within 4 ft of the east pier. Had a line been struck, the plan was to leave it, get everyone away upwind with no ignition and no vehicle started, and call the gas utility and 911 from a distance.
• New footings at 48 in. With the roof on its shores, the old piers came out and new ones went in with the bottom at 48 in below finished grade, measured and photographed in both holes, with a flared footing at the base and a smooth form tube up to grade to limit adfreeze, backfilled with clean crushed stone rather than the excavated silt. The holes were dug and measured from the surface with a post-hole auger and a tape on a rod; nobody climbed or reached head-first into a 4 ft hole in wet silt.
• Inspection actually held. The footing inspection was booked for the morning, the concrete for the afternoon of the following day, so a late inspector could not collide with the truck.
• Downspout moved to discharge onto a splash block 10 ft from the stoop, toward the side yard and not toward the neighbor's lot.
• Posts reset and flashing rebuilt. The shores were lowered in steps with both posts bearing, then removed only after the post bases were fastened.

The repair took 16 crew hours against 46 on the original job, about a third of the original labor, and the stoop pad was left in place after the soil under its east corner was dug out, re-compacted with stone and the pad re-supported, since its 3/4 in rise had dropped back to under 1/4 in on thaw.

What the shop changed

• A frost depth is a number on the drawing, copied from the jurisdiction's table with the county named, never "below frost".
• No pour without the footing inspection on the record, or a written okay from the department to proceed. The concrete is booked after the inspection, not before.
• Every jurisdiction the shop works in has a profile that carries its frost line depth, so the next county line is visible on paper. See related: The Jurisdiction Profile SOP.

References

• International Residential Code R403.1.4 and R403.1.4.1 (footing depth and frost protection), R403.3 (frost-protected shallow foundations) and Table R301.2(1), in the edition and with the values your jurisdiction adopted.
• USDA Natural Resources Conservation Service, Web Soil Survey, for soil type at a lot.
• The state one-call law, for locate requests and the notice period before digging.
• See related: Frost Depth and What It Sets; How to Find the Local Design Criteria for a Jurisdiction; Lot Drainage and Where the Water From Your Work Goes.