IRC R403.1 · Footings · 2021 / 2024 IRC

How to read IRC Table R403.1 footing size requirements

Soil bearing, stories, construction type, and the minimum footing rules — how to land on the right cell and what the table doesn't cover. Free link to the official code.

Need the actual table? Read Table R403.1 free at codes.iccsafe.org →

How to read Table R403.1, step by step

Step	What you do	Watch out for
1	Pick the table that matches the wall above: plain light-frame, light-frame with brick veneer, or light-frame with a concrete or masonry foundation/basement wall	Veneer and heavy walls add weight — they have their own table with bigger footings
2	Find the snow-load (or roof live load) band for your jurisdiction	The ground snow load comes from the jurisdiction’s Table R301.2
3	Find the row for your number of stories and foundation type (slab-on-grade, crawl space, or basement)	A basement adds wall and floor weight — it is a different row from a crawl space
4	Pick the soil-bearing column: a soils report value, or the presumptive value from Table R401.4.1 for the soil you actually have	Higher bearing capacity = narrower footing. Don’t pick a column the soil can’t back up
5	Read the cell: minimum footing width and thickness	The table is a minimum; the general minimums in R403.1.1 still apply
6	Set the depth: below the frost line from R301.2, and never less than 12 in below undisturbed ground	Frost depth is a local number, not in this table

Our own summary, not the code text. Look up Table R403.1 free at codes.iccsafe.org and verify against the IRC edition adopted by your AHJ. Not engineering advice — footings outside the prescriptive limits need a design professional.

Which rule answers which footing question?

Question	Where to look
How wide and thick?	Table R403.1 (by wall type, snow load, stories, soil bearing)
What bearing value can I assume without a soils test?	Table R401.4.1 presumptive values, by soil class
Absolute minimum size and projection?	R403.1.1
How deep?	R403.1.4 and the frost depth in Table R301.2
Reinforcing, anchor bolts, stepped footings?	The rest of R403.1 (and seismic provisions in higher seismic design categories)
Piers, columns, or point loads?	Not this table — size from the load and soil bearing, or get it designed

Worked example — one-story slab-on-grade home on clay, no soils report

Input / step	Value	Source
Soil found in the footing trench	Lean clay (CL)	Field observation
Soil bearing column to use	1,500 psf	Table R401.4.1 presumptive value for clay/silt classes
Why width depends on bearing (illustration)	A wall putting ~1,200 lb on each foot of footing needs 1,200 ÷ 1,500 = 0.8 ft of width	Load ÷ allowable bearing
Table R403.1 cell	Read the one-story, slab-on-grade row in the 1,500 psf column for your snow band	Table R403.1 (look it up)
General minimum check	Not less than 12 in wide and 6 in thick; projection at least 2 in and no more than the footing thickness	R403.1.1
Depth	Deeper of the local frost depth or 12 in below undisturbed ground	R403.1.4 + Table R301.2

Worked example values only. The 1,200 lb/ft load is an illustration of the concept, not a design load. Look up the table free at codes.iccsafe.org.

Common field mistakes

Mistake	What to do instead
Picking a high soil-bearing column because "it’s good dirt"	Use the presumptive value for the soil class you actually see, or a soils report
Using the plain light-frame table on a house with brick veneer	Veneer has its own table — the footing gets wider
Pouring on fill or disturbed soil	Footings bear on undisturbed soil or engineered, compacted fill
Treating the table cell as the depth	The table sets width and thickness; depth comes from R403.1.4 and the local frost line
Oversized projection on an unreinforced footing	Keep the projection past the wall no more than the footing thickness

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Sizing a residential footing the prescriptive way

Read Table R403.1 free at codes.iccsafe.org. ICC provides free read-only access to the IRC. This page explains how to use the footing tables; it does not reproduce them. It covers the 2021 and 2024 IRC — verify against the edition your AHJ adopted.

The concept is simple: load divided by what the soil can carry. A footing spreads the weight of the house over enough soil that the soil doesn’t settle. The IRC has already done that math for typical light-frame houses and put the answers in Table R403.1. You pick the table for the wall type, then the row (snow load, number of stories, slab/crawl/basement), then the column for your soil’s bearing value, and read the minimum width and thickness.

The soil column is where jobs go wrong. Without a soils report, you are limited to the presumptive values in Table R401.4.1 for the soil class you actually uncover. Clay and silt are presumed at 1,500 psf; sands and gravels and rock get higher values. Weaker, expansive, or questionable soils call for a soils investigation.

Worked example. A one-story slab-on-grade house is going on lean clay with no soils report, so you work in the 1,500 psf column. To see why the width matters: a wall that puts about 1,200 lb on each foot of footing needs 1,200 ÷ 1,500 = 0.8 ft of width, less than the code minimum, so the minimum governs — the footing is never less than 12 in wide and 6 in thick. Read the table cell for your snow band, use whichever is larger, and set the bottom below the local frost line and at least 12 in below undisturbed ground.

Related: find the local frost depth and snow load with the IRC R301.2 design criteria guide, check reinforcing with the rebar lap splice chart, estimate yardage with the concrete calculator, and run the pour with the concrete pre-pour checklist. Field PM keeps footing inspections and photos with the job.

FAQ

How wide does a residential footing need to be under the IRC?+

Table R403.1 gives the minimum width and thickness based on the wall type above, the snow load, the number of stories, the foundation type, and the soil bearing value. Whatever the table says, R403.1.1 sets a floor of 12 in wide and 6 in thick. Read the table free at codes.iccsafe.org.

What soil bearing value can I use without a soils test?+

Table R401.4.1 lists presumptive load-bearing values by soil class. Clay and silt classes (CL, ML, MH, CH) are presumed at 1,500 psf. If the building official suspects weaker soil, or the soil is expansive, a soils investigation is required.

How deep do footings have to be?+

Under R403.1.4 exterior footings go at least 12 in below undisturbed ground, and below the frost line the jurisdiction lists in Table R301.2 — whichever is deeper — unless you use a frost-protected shallow foundation or bear on rock.

Does Table R403.1 cover pier or column footings?+

No. It covers continuous footings under walls. Isolated pads under posts or columns are sized from the load they carry and the soil bearing value, or by a design professional. For deck footings, see the AWC DCA 6 guide.

Did Table R403.1 change in recent editions?+

Yes. Earlier IRC editions used a single simple table; newer editions split it into several tables by wall type and added snow-load bands, so footing widths now respond to the local snow load. Read the edition your AHJ enforces.

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