Quick Verdict
The spread footing vs continuous footing question is really a question about which dig your plans call for. A spread (or isolated/pad) footing sits under a single post or column and carries that point load down into the soil, so it is excavated as an individual hole or pit. A continuous (or strip) footing runs under a wall, spreading the wall's load along its length, so it is excavated as a perimeter trench. Knowing which one your plans show, individual pits versus a connected trench, tells you and your excavator exactly what to dig.
What Each Footing Does
A footing's job is to spread a structure's weight over enough soil that the ground can carry it without sinking. The shape of the load decides the shape of the footing:
- Point loads (a post, a column, a deck pier) push down at a single spot, so they get a spread/pad footing, a square or rectangular block of concrete directly under that point.
- Line loads (a wall) push down along a line, so they get a continuous/strip footing, a long ribbon of concrete that runs under the whole wall.
Recognizing which your plans call for is the first step in any foundation excavation job.
Spread (Isolated) Footings: Individual Holes
A spread footing is excavated as a discrete pit at each post or column location. The plans specify the size and depth of each pad based on the load and the soil's bearing capacity. The excavator digs each hole to the dimensions on the plan, the bottom is leveled and verified as firm bearing soil, and rebar and concrete follow. Because each is separate, the dig is counted by hole, not by length.
Spread footings are common under post-frame buildings (pole barns and shops), deck posts, and columns. The closely related case of holes for posts and piers is covered in pier and post foundation holes.
Continuous (Strip) Footings: Perimeter Trenches
A continuous footing is excavated as a trench that follows the wall line, usually the full perimeter of a house plus any interior bearing walls. The trench width and depth come from the plans, and the bottom must be flat, level, and on undisturbed bearing soil so the wall load is carried evenly. Rebar runs along the trench and concrete is poured in one continuous element.
Strip footings are the standard under stem-wall houses and any continuous masonry or concrete wall. They feed directly into the wall above, covered in stem-wall foundation excavation.
Combined and Mat Footings at a Glance
Two more types show up on plans and change the dig again:
- Combined footing: one footing supporting two or more closely spaced columns, used when their pads would otherwise overlap.
- Mat (raft) footing: a single large slab under the whole structure, used on weak or variable soils to spread the load over the maximum area. The dig is a broad, shaped excavation rather than holes or a narrow trench.
Side by Side
| Footing type | Supports | How it's dug | Counted by |
|---|---|---|---|
| Spread / pad (isolated) | A single post or column | Individual holes/pits | Number of holes |
| Continuous / strip | A wall | Perimeter/wall-line trench | Linear feet of trench |
| Combined | Two or more close columns | Larger shared pit | The pit |
| Mat / raft | The whole structure | Broad shaped excavation | Area |
How to Read Your Plans
You do not need to be an engineer to spot which dig you have:
- Look at the foundation plan. Square or rectangular pads drawn at points are spread footings; a continuous line under walls is a strip footing.
- Check the footing schedule. It lists pad sizes (for spread footings) and footing widths/depths (for strip footings).
- Match loads. Posts and columns get pads; walls get strips.
- Note the soil note. A geotech or soils note may upsize pads or call for a mat where bearing is weak.
The Oregon Soil Factor
Soil bearing capacity sets the footing size, and it varies across Oregon. Soft, wet Willamette Valley clay has lower bearing capacity, so pads are larger and trenches may be wider or deeper to spread the same load; weak ground can even push a design toward a mat footing. Firmer Central Oregon ground over rock supports more on a smaller footing. This is why two identical buildings can have different footing digs in different parts of the state.
What It Costs to Dig
The pricing logic differs by type: spread footings are priced by hole count and depth, continuous footings by trench length, width, and depth.
Industry Baseline Range: an excavator plus operator runs roughly $150 - $350+ per hour, and trenching runs roughly $8 - $40+ per linear foot depending on width, depth, and soil. Hole-by-hole pad digs are quoted by count and depth.
These are industry baseline ranges for planning only -- actual pricing depends on site conditions, soil, access, depth, haul-off, and current market conditions. Get a site-specific quote.
Current Market Reality
Costs climb when soft clay forces larger pads or deeper trenches, when water table floods the dig, or when soft bearing soil has to be undercut and replaced. Small jobs carry a $500 - $1,500+ minimum once mobilization is added.
Frost Depth and How Deep Footings Go
Whichever footing type you have, one thing sets how deep it must be dug: the frost line, plus the bearing requirement. A footing has to sit below the depth that frost reaches in winter, because freezing soil heaves and would lift and crack the foundation. This is why footing depth varies across Oregon:
- East of the Cascades, colder winters drive a deeper frost line, so footings are dug deeper and frost-protection detailing comes into play.
- In the milder Willamette Valley, the frost line is shallower, but soft, wet clay and the need for firm bearing can drive depth instead.
- On rocky ground, the footing may bear on or near rock at a shallower depth, but reaching uniform bearing can require extra work.
So the dig depth is the greater of "below frost" and "down to firm bearing soil." Both spread and continuous footings follow this rule, your plans and local code specify the depth, and the excavator digs to it. Going shallower to save time is exactly the kind of shortcut that causes heave and settlement later.
Getting the Bottom of the Dig Right
For both footing types, the quality of the dig comes down to the bottom of the excavation, because that is where the foundation meets the soil. A few principles apply regardless of whether you are digging holes or a trench:
- Flat and level. Spread footing pits and continuous trenches both need a flat, level bottom so the concrete bears evenly.
- Undisturbed bearing soil. The bottom should be firm, undisturbed native soil, not loosened or smeared.
- No loose backfill under the footing. Over-dig is corrected with compacted material or a step, never loose fill.
- Dry enough to pour. Water and soft mud in the bottom have to be dealt with before concrete goes in.
These are the details an inspector checks before the pour, and they matter as much as the layout. A perfectly laid-out footing dug onto soft or uneven ground still settles. Whether your plans call for individual pads or a continuous trench, the bottom of the dig is where a foundation is won or lost, which is why an experienced excavator finishes the bottom carefully rather than just getting close to depth.
The Bottom Line
Spread footings mean holes under points; continuous footings mean trenches under walls, and your plans tell you which. Once you know, an excavator can dig it to spec on the right bearing soil. To plan your foundation dig, see our excavation services or request a free estimate.