How is basement excavation priced?

Three ways: per linear foot of trench for work along an existing wall, per cubic yard of soil for a full dig, or per machine day plus operator when access is poor. All three rest on the same volume, so take off your own cubic yards first — length × width × depth ÷ 27 — and ask each bidder which unit their number uses.

How many cubic yards of soil come out of a trench along my foundation?

Multiply the run length by the trench width by the depth to the footing, then divide by 27. A 78 ft run, 3 ft wide, 7.5 ft deep is 1,755 cubic feet, or 65 bank cubic yards. Add roughly 20–30% swell for hauling, since loose soil takes up more room than it did in the ground.

Can you dig out and lower an existing basement?

Yes, by underpinning (extending the foundation deeper in sections) or benching (lowering only the middle and leaving a sloped shelf against the wall). Both are engineered, permitted, structural jobs and are the most expensive form of residential excavation. Benching costs less but gives up floor area; underpinning keeps the footprint.

How much does it cost to lower a basement floor per square foot?

This site stores no rate, because that one moves further and faster than almost any other — it turns on your soil, your access, the depth you are dropping to and, above all, whether the job is underpinned or benched. What you can do before quoting is measure the two quantities the price attaches to: the perimeter in linear feet that would be underpinned, and the floor area in square feet. With benching, check whether a per-square-foot figure is quoted on your existing footprint or on the smaller finished floor — that alone can make two bids look far apart when they are not. Put your own quoted figures through the cost-per-square-foot normalizer to compare them on the same basis.

Is underpinning or benching cheaper?

Benching, usually and by a clear margin, because the footings are never undermined — the crew lowers the middle of the floor and leaves a sloped shelf of soil supporting the wall. The saving is paid for in floor area, and the shelf gets wider the deeper you go. Underpinning keeps the full footprint but extends the foundation deeper in sequenced sections, which is slower and more expensive. A licensed structural engineer decides which is even possible on your house before cost enters the conversation.

Do I need a permit to excavate around my foundation?

Usually yes for anything that exposes or affects the foundation, and always for work that goes under a footing. Rules vary by jurisdiction, so confirm with your local building department before scheduling. Regardless of permits, have utilities located first — that service is free and required almost everywhere.

Why is one excavation quote double another for the same hole?

Almost always access, spoil and restoration rather than the digging itself. A machine that can reach the wall, spoil that stays on site as backfill, and a lawn nobody has to rebuild make a dig cheap; a hand-dug trench, seven truckloads to a tip and full landscape restoration make the same hole expensive. Compare the exclusions, not just the totals.

Basement excavation cost: what moving the dirt actually costs

Excavation is the one below-grade line item nobody measures before the quote arrives. It is worth measuring: dig volume is simple geometry, and once you know your cubic yards you can tell a fair number from a guess.

By Francesco Zinghinì

Excavation is priced three different ways, and knowing which one your contractor is using is half the battle. Small foundation work is usually quoted per linear foot of trench; a full dig is quoted per cubic yard of soil moved (or as a lump sum built from cubic yards behind the scenes); and awkward, small or interior work is quoted per machine day plus operator, because the crew cannot work efficiently enough for volume pricing to be fair. Whichever unit appears on the page, the underlying quantity is the same, and you can compute it yourself before the first crew walks the lot.

The take-off: figure your cubic yards first

Every dig reduces to a box of soil. Measure it and divide by 27, because there are 27 cubic feet in a cubic yard:

bank cubic yards = length (ft) × width (ft) × depth (ft) ÷ 27

That gives bank volume — soil as it sits in the ground, undisturbed. Dug soil is loose and takes up more room than it did in the hole, so haul-away is figured on loose volume. The planning convention is a swell allowance of roughly 20–30% for ordinary clay and loam, and more for rock. Divide the loose volume by the truck size to get load counts. The cubic-yard conversions table holds the same ÷ 27 math you will use again for slab and footing concrete.

A worked example: excavating three walls for waterproofing

Say you are digging along 78 linear feet of foundation wall to expose it for exterior waterproofing. The trench is opened to 3 ft wide at the bottom so a person can work against the wall, and the footing is 7.5 ft down.

78 × 3 × 7.5 = 1,755 cu ft, and 1,755 ÷ 27 = 65 bank cubic yards.

Add a 25% swell allowance and you are handling 65 × 1.25 ≈ 81 loose cubic yards. A typical tandem dump truck carries somewhere around 12 cubic yards, so that is 81 ÷ 12 = 6.75, rounded up to 7 truckloads if the spoil leaves the site. If most of it can be stockpiled on the lot and pushed back as backfill, most of those loads — and their disposal fees — disappear. That single question, where does the dirt go, moves excavation quotes more than almost anything else.

Now price it. If the quote is per foot of wall, 78 ft at the rate in your quote is the whole line. If it is per cubic yard, apply your rate to the 65 bank yards (confirm which volume the rate refers to — bank or loose — because the two differ by a quarter). The exterior waterproofing calculator takes the excavation as its own line so you can see it separately from the membrane, and the contingency planner puts a buffer on top, which digging deserves more than any other trade.

Three jobs that all get called "basement excavation"

Digging to expose an existing wall. The most common case: a trench along one or more walls, down to the footing, so the outside face can be sealed, drained and backfilled. Volume is modest, but depth makes it hazardous and access decides the price. See the guide on interior drain tile versus exterior waterproofing before you commit to going outside at all.
Digging a new basement or a basement under an addition. An open-site dig of the full footprint plus working room around it, with the spoil either stockpiled or hauled. Volume dominates, and the rest of the structure — footings and slab — follows straight behind it.
Lowering an existing basement. Digging down inside a finished house to gain headroom, either by underpinning (extending the existing foundation deeper in sections) or by benching (leaving a sloped shelf of undisturbed soil against the wall and only lowering the middle). This is the expensive one, it is engineered work, and it overlaps with piering and underpinning. Benching is cheaper but costs you floor area; underpinning keeps the full footprint at a much higher price per foot.

Lowering an existing basement: underpinning vs benching

Of those three jobs, lowering a basement floor to gain headroom is the one people underestimate most, because it sounds like digging and is actually structural work. The floor of a basement sits above the footings that carry the house. Go below them and the foundation has to be extended down first — or deliberately left alone and worked around. That choice is the whole cost story.

Underpinning extends the existing foundation deeper in short, alternating sections, each one excavated and poured before the next is opened, so the wall is never unsupported along its length. You keep every square foot of the footprint. It is slow, sequenced, engineered work, and it is the expensive option.
Benching leaves the footings where they are and lowers only the middle of the floor, keeping a sloped shelf of undisturbed soil against the wall to hold it up. It is markedly cheaper because the foundation is never undermined — but the bench eats into the room, and the deeper you go the wider it gets. You are trading floor area for headroom.

Both are permitted work designed by a licensed structural or geotechnical engineer. Neither is a job you scope from a web page.

Take off the two quantities before you call

Quotes for this work arrive in mixed units — per linear foot of wall underpinned, per section or pin, per square foot of finished floor, or a lump sum — which is exactly why bids look incomparable. Two measurements make them comparable, and you can take both yourself:

Perimeter, in linear feet — the run of wall that would be underpinned. This is what a per-foot underpinning number multiplies.
Floor area, in square feet — what a per-square-foot number multiplies. With benching, note that the usable area after the job is smaller than the area you measured, so a per-sq-ft price quoted on the old footprint and one quoted on the finished floor are not the same number.

Then add the depth you are dropping the floor by, multiply it through the area, and you have the spoil volume in cubic yards using the same ÷ 27 take-off as above — every bucket of which has to come up a stairwell or a window opening rather than out on a machine, which is why interior digging is priced so differently from an open-site one. Put the resulting figures side by side with the cost-per-square-foot normalizer, price the piering portion with the piering & underpinning calculator, and carry a larger buffer than usual in the contingency planner: opening the ground beneath a house is where unknowns actually live. Finish by pricing the new slab and the interior drain tile that a newly lowered floor almost always needs, since you are now sitting deeper relative to the water table than the house was designed for.

What actually moves the number

Volume sets the floor. These set the ceiling:

Access. A machine that can drive to the wall works ten times faster than a crew hand-digging a trench between a fence and a deck. If the only way in is through a gate, expect mini-excavator rates or hand labor.
Soil and rock. Loam digs fast, heavy wet clay digs slow, and hitting rock changes the method entirely. Ask what happens, and at what rate, if rock appears — that clause belongs in the quote, not in a conversation on day three.
Water. A high water table means pumping and a muddier, slower dig, and it changes what the finished drainage has to do. Pair the dig with the French drain take-off so the pipe and gravel quantities are priced with the trench, not after it.
Spoil disposal. Hauling and tipping fees are per load and per site, and contaminated or unsuitable fill costs more to place. Keeping clean spoil on site to reuse as backfill is the single largest saving available on most residential digs.
Shoring and protection. Deep trenches need sloping, benching or a trench box, and neighboring structures may need protection. That is safety work, not padding.
Restoration. Compacted backfill, regrading so the finished soil slopes away from the house, and replacing lawn, beds or paving. Read every quote for whether restoration is in or out; two bids that look far apart often differ only here.

Measure before you call, and ask the same questions of everyone

The order of operations that saves money is unglamorous. Measure the run and the depth to the footing. Compute your bank cubic yards. Decide, in advance, whether spoil stays on site. Then ask every bidder for a quote broken into excavation, the work in the hole, backfill and restoration, with the unit named — per foot, per cubic yard or per day. Quotes given in different units are not comparable until you convert them, and the cost normalizer is there for exactly that. Anything a bidder excludes should appear in writing as an exclusion, not as a surprise.

The safety and permit part, which is not optional

Excavation is the most dangerous work on a residential site: an unsupported trench wall can collapse without warning, and soil is far heavier than people expect. Trenching and excavation are governed by workplace safety rules on sloping, benching and shoring, and a competent contractor will talk about them before they talk about price. Have utilities located before any digging — the national call-before-you-dig service is free and using it is the law in most places. Digging next to or beneath a foundation is structural: undermining a footing, or lowering a basement floor below it, must be designed by a licensed structural or geotechnical engineer and built by licensed pros under permit and inspection. If cracks, bowing or movement are what sent you looking at excavation in the first place, the engineer comes before the estimate, because the diagnosis chooses the method and the method sets the cost.

Why there is no price per yard on this page

Excavation rates swing with fuel, tipping fees, machine availability and how far your site is from a disposal point — they are local and they move. So this site stores none. You bring the rate from your own quote; the geometry above does not change, so the arithmetic stays correct indefinitely. Everything here is a planning estimate from your own figures, not a bid: get itemized written quotes from licensed contractors before you commit.

On the safety and code side: OSHA publishes the trenching and excavation requirements crews work to, call 811 is the national call-before-you-dig service for utility locates, and the International Code Council publishes the model codes your local building department adopts and enforces.