Footing Types Explained: Strip, Spread, Pad, and Trench Footings

Every residential foundation is some combination of four footing types. They differ in shape, in where they go, and — critically for anyone doing a takeoff — in whether they are measured by the foot or counted by the unit. Get the type wrong and the quantity is on the wrong basis before you even start adding.

Here is what each one is, where it shows up in residential work, the verified code minimums, and what it means for your numbers.

Strip footings (continuous wall footings)

A strip footing is a continuous ribbon of concrete running under a load-bearing wall. It is the most common footing in residential construction — every foundation wall in a basement sits on one. The strip is wider than the wall it carries so the load spreads over enough soil, and it runs the full length of the wall.

Typical residential strip footings run 16 to 24 inches wide and 6 to 10 inches thick, poured continuously along the wall line. The 2021 IRC minimum is 12 inches wide and 6 inches thick (R403.1.1), with the width driven up by soil bearing value and story count. In Ontario, Table 9.15.3.4 sets minimum strip widths of 250 mm for one storey, 350 mm for two, and 450 mm for three (roughly 10, 14, and 18 inches).

Takeoff: measured in linear feet along the wall line. Strip footing quantity is the heart of a residential footing takeoff.

Spread footings

Spread footing is the general category for any footing that spreads a concentrated load over a wider area of soil — the name describes the job, not a single shape. In residential work the term most often means an isolated spread footing: a single square or rectangular pad under a column or post. (A continuous strip footing is technically a spread footing too, spreading a wall load, but in the field “spread footing” usually points to the isolated kind.)

The 2021 IRC requires spread footings to be at least 6 inches thick (R403.1), with the projection beyond the supported element at least 2 inches and no greater than the footing thickness. Size in plan is driven by the column load and the allowable soil bearing pressure.

That projection rule is worth understanding because it sets the shape of the pour. The “projection” is how far the footing sticks out past the column or wall on each side. The code says that overhang has to be at least 2 inches — enough to actually spread the load — but no more than the footing’s own thickness, because a footing that projects farther than it is thick starts to fail in bending at the edge rather than bearing cleanly on the soil. So a 6-inch-thick footing can project up to 6 inches per side; a wider spread needs a thicker footing to match. On the plan this is why bigger point loads get both wider and deeper pads, not just wider ones.

Takeoff: an isolated spread footing is counted as a unit, like a pad.

Pad footings (isolated / pier pads)

A pad footing is the residential name for the isolated spread footing you meet most often: the square concrete pad under an interior post that carries the main beam. It is the same idea as a spread footing, sized for a point load rather than a wall.

Residential interior pads commonly run from about 38” × 38” up to 46” × 46”, and 12 to 19 inches deep, though a smaller 24” × 24” pad 8 to 12 inches deep is common under a single steel telepost where the footing only needs to reach undisturbed soil, not the frost line because it is inside the heated basement. Interior columns in a detached one- or two-family dwelling of three stories or less may use plain (unreinforced) concrete footings under the IRC.

Takeoff: counted as units, never linear feet. This is the rule estimators break most — a pad billed as a few linear feet of footing is a quantity error every time. The footing takeoff guide covers exactly why pads and linear runs are kept on separate lines.

Trench footings (trench-fill footings)

A trench footing, or trench-fill footing, is more a method than a distinct shape. Instead of forming a shallow footing and building a stem wall on top, the crew digs a narrow trench to the required depth and fills much or all of it with concrete in one pour. The footing and the below-grade wall become a single mass of concrete.

Trench fill is efficient for long straight runs and firm soil, because a backhoe digs the trench fast and there is little forming. It shows up in residential work on garage grade walls, some porch foundations, and in regions where the technique is standard. Depth is governed by frost: the IRC requires exterior footings at least 12 inches below undisturbed grade, and below the local frost line where that is deeper (R403.1.4).

Takeoff: measured in linear feet along the run, like a strip footing — the extra depth changes concrete volume, not the length you bill.

Grade beams (briefly)

A grade beam is a reinforced concrete beam that spans between support points — piers, piles, or pile caps — rather than bearing continuously on soil. It is designed for bending, unlike a wall footing that transmits load straight down, and shows up in residential work on sloped sites, over expansive clay, or wherever a pier-and-beam system replaces a continuous footing. Because it carries the wall across weak soil to the piers, it is always heavily reinforced.

Takeoff: measured in linear feet along the beam, like a strip footing, with the supporting piers counted separately as units.

Type-to-takeoff summary

Why the type matters before you measure

The type decides the unit of measure, and the unit of measure decides the invoice line. Strip, trench, and grade-beam runs go on the linear-foot line; spread and pad footings go on the count line. A residential foundation mixes them — a basement wall on strip footings, teleposts on pad footings, maybe a garage on trench fill — so a clean takeoff sorts every element into the right bucket before adding anything.

When a plan is ambiguous about which line is a continuous wall footing and which square is an isolated pad, the wall schedule and the section details settle it. The field guide to reading footing plans covers how to tell them apart on the drawing. Automated tools like FootingTakeoff classify each element for you and keep the linear runs and the pad count on separate lines, which is exactly how the invoice needs them.