The International Residential Code requires exterior footings, piers and permanent supports to be protected from frost by extending below the local frost line or by using an approved frost‑protection method such as a frost‑protected shallow foundation (FPSF); check the adopted IRC edition and any local amendments for the numeric frost depth your jurisdiction enforces[1].
Frost depth varies substantially by region and local conditions, so use your local building department's adopted frost‑depth number or regional maps rather than relying on a generic rule of thumb[7][8][1].
Cast‑in‑place concrete footings (sonotubes)
Cast‑in‑place concrete footings using sonotubes are the common, widely accepted solution for decks in frost areas because they place bearing below the frost line, provide the required bearing area, and allow standard post‑to‑footing connectors; installation requires excavation, formwork, concrete and curing per code and inspector directions[5][1].
Precast piers
Precast piers can be used if the bottom of the pier bears on undisturbed competent soil and the pier bottom is installed below the local frost line; follow the manufacturer's installation specifications and verify bearing before accepting the pier as the footing solution[5][1].
Precast 'surface' deck blocks
Precast 'surface' deck blocks are fast to install but are typically not code‑compliant for elevated decks in frost areas because they sit at or above grade and do not place bearing below the frost line, which makes them vulnerable to frost heave; check your local code for possible exceptions for very low, free‑standing structures[1][8].
Helical (screw) piers
Helical piers are an engineered alternative often used in poor or wet soils or tight sites: they can provide reliable axial and lateral capacity with less excavation, but unit costs are higher and installations should follow manufacturer and engineer guidance[5].
Driven piles or deep cast piers
When shallow soils cannot provide adequate bearing or when greater axial or lateral capacity is required, driven piles or deep cast piers are appropriate engineered solutions that should be selected with geotechnical input and IBC guidance[2].
Soil bearing, site review, and when to get a geotechnical report
The International Building Code publishes presumptive allowable bearing pressures (Table 1806.2) that many jurisdictions accept for footing sizing without a geotechnical report; softer soils such as high‑silt or organic soils have much lower tabulated values than compact sand, gravel or rock, so consult the table or a geotechnical engineer when soils look marginal[2].
Use the USDA NRCS Web Soil Survey as a free, site‑specific starting point to evaluate soil types and drainage that affect bearing and footing choice; when in doubt about bearing capacity or problematic fill, obtain a geotechnical report[6][2].
Frost‑Protected Shallow Foundations (FPSF): when they help and the rules
Frost‑Protected Shallow Foundations are an approved alternative that can permit much shallower footing depths only when designed and installed per ASCE 32 or HUD's FPSF design guide — they are prescriptive about insulation placement, widths and inputs and cannot be used informally without following the standards or a stamped design[3][4].
Prescriptive installation sequence for a typical cast‑in‑place deck pier
- Obtain required permit and mark pier locations per the approved plan[5][1].
- Excavate to the required depth (below the local frost line or as shown on engineered drawings) and verify bearing on undisturbed soil[5][1].
- Place compacted base if required, set the sonotube or form, and position any required rebar or anchors per the plan/specs[5].
- Pour concrete, allow proper curing time per inspector or product guidance, then install a corrosion‑protected post base or anchor and the post attachment hardware[5][1].
- Request the required inspections at code checkpoints (pre‑pour and final as required by the local jurisdiction)[1].
Local numeric requirements (frost depth, footing dimensions, and required inspections) and the specific product manufacturer's installation requirements control acceptability — always confirm with your local building department and the product documentation prior to purchase and installation[1][5].
- Confirm the local adopted frost depth (building department or regional maps) and use that depth for footing placement unless using a properly designed FPSF[1][7].
- Inspect the soil at footing depth for signs of fill, high organic content, or loose material; if present, get a geotechnical assessment or plan to remove and re‑compact to an engineered specification[2][6].
- Check site drainage and grade near footings and posts; poor drainage or concentrated runoff near footings increases frost heave risk and undermines bearing. For practical fixes to low spots and poor drainage without full regrading, see our piece on fixing low spots and poor drainage without full regrading where small corrections may reduce long‑term movement.
Costs and budgeting
Different footing methods (cast‑in‑place, precast, helical piers, driven piles) have substantially different labor and equipment costs; free online consumer cost guides and professional estimators can help develop a ballpark budget but regional quotes are essential because site conditions drive price variability[10][11].
When to involve professionals
Obtain a geotechnical report if the site has questionable soils, undocumented fill, high groundwater, or if the deck loads are large; rely on an engineer and manufacturer guidance for helical piers, driven piles, deep cast piers, or any FPSF design[2][4][5][3].