The Short Answer: You Need Both, In This Order
If you came here to decide which material to order by the truckload, here is the answer so you can go make the call. Compacted fill dirt builds the bulk of the pad and gets the building up out of the water. Crushed gravel goes on top of that as the surface you drive on and the layer that lets water move. It is not an either or question. It is a question of what goes where.
The reasoning is mostly about cost and behavior. Fill dirt is subsoil from local excavation, screened of debris, with almost no organic matter left in it. That is why it compacts tight and stays put, and it sits in the low price band compared to crushed stone. If you need to raise a low spot a foot, doing it in stone is spending good money to bury rock where nobody will ever see it or need it.
Gravel earns its price at the top. Crushed stone has angular faces that wedge against each other and lock, and the voids between pieces give water somewhere to go. Dirt does neither of those things once it is wet and a loaded tire is turning on it. Wet subgrade with no stone cap is how you get a floor you avoid in March.
The two failure modes worth naming are the ones people actually lose sleep over. One is a pad that keeps settling after the building is up, which shows as cracks if you poured a slab and as low water holding spots if you went with a gravel floor. The other is rutting, where the first loaded tractor that turns around inside the door leaves a trench. Both of those come back to the same two habits, which are stripping the organics and compacting the fill in thin lifts.
Key takeaway: fill dirt for elevation and bulk, crushed stone for the surface you drive on.
Strip the Topsoil First, Or Nothing Else Matters
Topsoil is dark because it is full of organic matter, and organic matter keeps breaking down for years after you cover it. It does not matter how well you compact everything above it. If you leave a layer of decaying material at the bottom of the pad, the pad will settle, and it will settle unevenly because the organic content is not uniform across the footprint.
Common practice is stripping 6 to 12 inches of topsoil off the footprint before any fill goes down, and going until you hit firm subsoil. On some sites that happens fast. On others, especially old pasture or a former garden area, you are digging deeper than you planned. The depth is set by the ground, not by a number on paper.
Do not pay to haul that topsoil away if you have anywhere at all to put it. Stockpile it out of the build zone. You will want it for finish grading around the building, for repairing the lawn the trucks tear up, and for beds later on. It is the same material people order by the yard, and you are standing on a pile of it for free.
Sod is the same problem in a thinner package. Building a pad over grass traps a layer of green material right at the interface you least want soft. Strip it with the topsoil.
The other thing to settle before the first load shows up is drainage. Where does water currently cross the site when it rains hard. Where does it pond. Where does it leave. Those answers determine where the pad sits and how high it needs to be, and they are much cheaper to act on before there are thirty loads of dirt in the way.
Layer One: Compacted Fill Dirt for the Bulk Lift
Fill dirt is subsoil, screened of debris, and it is a structural material rather than a growing medium. That is not a limitation here. It is exactly the property you want under a building. Nothing needs to grow in it, and the absence of organics is what lets it compact tight and stay at the elevation you put it at.
Place and compact in 6 to 8 inch lifts
If you take one thing from this article, take this one. Place fill in 6 to 8 inch lifts and compact each lift before the next one goes on. Dumping three feet of dirt and running a plate compactor across the top does nothing below the first few inches. The surface will look firm and feel firm, and everything under it will still be loose.
Uncompacted fill settles for years. Under a slab that settling turns into cracks, because the concrete ends up bridging a void that was not there on pour day. Under a gravel floor it turns into dish shaped low spots that hold water and break down the stone above them. Neither is fixable from the surface later without tearing something up.
A plate compactor is workable on a small pad with thin lifts. A larger pad wants a roller, and if you are hiring the excavation out, the contractor will have one. Moisture matters too. Slightly damp fill compacts better than bone dry fill, and soaked fill does not compact at all. If the subgrade is pumping and rolling under the equipment, it is too wet to build on that day.
How much fill dirt you actually need
Fill dirt runs about 1.3 tons per cubic yard, and one cubic yard covers about 54 square feet at 6 inches deep. Typical install depth for fill dirt is 6 to 12 inches, though a barn pad going in on low ground can easily take more than that.
Work an example. A 30 by 40 pad is 1,200 square feet. At 6 inches deep, 1,200 divided by 54 is about 22 cubic yards, and 22 times 1.3 is about 29 tons. At 12 inches deep you are covering half as much ground per yard, so 1,200 divided by 27 is about 44 cubic yards, and 44 times 1.3 is about 58 tons. Run the same two steps with your own square footage and you have both numbers.
Then order more than that. Compaction pulls volume out of the pile, the existing ground is never as flat as the tape says, and the pad should extend past the building on every side. A little extra dirt is a problem you can grade out. Running short in the middle of placing lifts is a problem that costs you a second delivery.
Layer Two: Crushed Gravel as the Wearing Course
Once the fill is placed and compacted to grade, the stone goes on. This is the layer that makes the difference between a barn floor you use every month of the year and one you plan around.
What depth to run
A common target is 4 to 6 inches of compacted crushed stone across the footprint. Read that as a compacted number, not a delivered number. Loose stone loses height when it is rolled, so order enough material to land at the compacted depth rather than enough to look right when it comes off the truck.
The soil under the pad moves that number. Clay subgrade and anywhere sod was left in place go soft and want more rock. Sandy, well draining ground needs less. If you are not sure which you have, dig a hole after a hard rain and see how long water sits in it.
Which stone to order
A lot of post frame builders run two aggregates instead of one. A coarse base layer goes down first, something like a #2 gravel, and then a finer crushed stone top course goes over it and works down into the voids. The fines are what lock the coarse rock in place and give you a surface that is drivable rather than loose and rolling under foot.
Whatever size you land on, buy crushed and not round river rock. Angular faces wedge together and hold. Rounded stone shifts under a turning tire and never really locks, no matter how deep you put it down. That single distinction matters more than the exact gradation number on the ticket.
It is worth being honest that the stone is technically optional. Plenty of barns sit on bare compacted dirt and always have. What the stone buys you is a floor that drains, does not track mud into the building, and holds up in the wet months.
If a concrete slab is in the plan, do not skip the stone on the theory that the concrete is the floor. The compacted stone base gives the slab a uniform bearing surface across the whole footprint and a drainage path underneath, so the slab is not curing and then living on saturated soil.
How Depth Changes With What You Park In There
Size the section for the heaviest thing that will regularly sit on it or drive across it. Not the average, and not what is in there today.
Light duty looks like garden equipment, a car, shelving, boxes, and foot traffic. Over well compacted fill, the lower end of the compacted stone range usually holds up fine for that.
Heavy duty is a tractor with a loaded bucket, a skid steer, a loaded trailer, or a truck. Those loads come through a small tire contact patch, and concentrated loads find any soft spot in the pad. Go to the upper end of the stone depth for that use, and be stricter about the fill compaction below, because that is where the load is actually carried.
Here is the concept people get backwards. Gravel spreads load, but it does not create bearing capacity. A thick stone layer over soft uncompacted fill still ruts, because the stone just follows the soft material down. Depth is not a substitute for compaction. If you have to choose where to spend effort, spend it on the lifts.
Rutting also shows up in predictable places. Doorways, the turn just inside the door where equipment pivots, and anywhere water collects. It is reasonable to run a deeper stone section at the door approach and along the main drive lane and leave the corners at the standard depth.
Season matters more than people expect. A pad built on clay in a wet spring does not behave like one built in late summer. If the subgrade is flexing and pumping under a loaded truck, stop and let it dry instead of pushing material into mud.
Pad Size, Grade, and Drainage
Build the pad wider than the building on all four sides. That shoulder keeps the edge from sloughing off as it weathers, gives the crew somewhere to stand and set posts, and protects the perimeter from washing out in a storm. A pad cut exactly to the footprint starts losing its edges immediately.
Slope the finish grade away from the building on every side. A 2 to 4 percent fall away from the pad is the usual target. Flat is not good enough, because flat plus a season of settlement becomes a shallow bowl. A pad that ends up level with the surrounding ground will take on water at the edges every time it rains hard, which undoes the elevation you paid to build.
Roof water is its own problem. It concentrates at the drip line in a narrow band, and it arrives with force. Decide where that water is going before the building is up rather than after you see the trench it cut along one wall.
Estimate the driveway and the approach apron separately from the building pad. Different traffic pattern, often a different depth, and rolling both into one number is the most common way people come up short. Two numbers on the order are easier to fix than one number that was wrong.
More than any extra inch of stone, a pad that sits high and sheds water is what keeps the floor usable.
Ordering Without Buying the Wrong Material Twice
Sequence the deliveries in the same order as the work. Strip first, then fill in lifts with compaction between each one, then stone last. Stone that shows up before the fill is compacted gets pushed around, mixed into soft dirt, and effectively lost.
Bulk material is sold by the ton or by the cubic yard depending on the supplier and the product, which makes quotes hard to compare side by side. Use the density to put them on the same basis. At about 1.3 tons per cubic yard, fill dirt converts either direction with one multiplication, and the same trick works when you are pricing crushed gravel for the top course.
Order a margin over your calculated number on both materials. Compaction takes volume out of the pile, the ground underneath is never as even as you measured, and a second small delivery almost always costs more per yard than including that material in the first load.
Think about truck access before you order anything. Where can a loaded truck get in, where can it dump, can it back onto ground that is currently soft, and where can the stockpile sit without blocking the build. On a rural site the answer is often that everything has to come in from one direction, which changes how you stage the piles.
Finally, sort out who owns the pad. Site prep is frequently handled by an excavation contractor who is not the barn builder. Confirm with the builder what finished elevation they want and what depths they expect, and get that agreed before the first truck rolls in. That conversation takes ten minutes and prevents the expensive kind of surprise.
How We Started
We started Mulch Mound because we got tired of the hassle that came with buying landscaping materials. The options were either loading bags into your car at a garden center or calling around to local suppliers, trying to figure out pricing, minimums, and delivery schedules. Neither option felt convenient or transparent.
Three of us – Alec, Mo, and Tyler – decided there had to be a better way. Alec and Tyler got their start back in 2013 running a landscaping business during college, moving mulch and mowing lawns to pay tuition. That experience taught them how frustrating it was to source materials, and years later, that frustration turned into Mulch Mound.
We focus on making it simple to get mulch, stone, and soil delivered directly to your home. Order online, pick your delivery date, and we handle the rest. No loading bags. No calling multiple suppliers. No wondering if you bought enough or paid a fair price.
We work with quality local suppliers in the areas we serve and aim to be straightforward about what we offer and what it costs. Landscaping is hard work. Buying the materials for it shouldn't be.
Frequently asked questions
Do I have to strip topsoil if the site is already high and dry?
Elevation does not fix organics. A high site with a foot of dark soil over it will still settle as that material breaks down, and it will settle unevenly because the depth of the dark layer varies across the footprint. Dry ground just means you will be less miserable doing the stripping.
The exception worth mentioning is a site that has already been cut down to subsoil by previous excavation, such as ground that was graded for an earlier building or a driveway cut. If you are already standing on firm subsoil with no dark layer, there is nothing left to strip.
Can I skip the gravel and pour a slab directly on compacted fill?
Some people do. The argument for the stone is that it gives the slab a uniform bearing surface and a path for water to move underneath instead of sitting against the bottom of the concrete. There is also a practical reason that does not get mentioned enough. Stone is far easier to fine grade to a flat plane than dirt is, and a slab poured over a plane that is flat to begin with takes less concrete and ends up more consistent in thickness.
What if I already have a pad that settled?
Resist the instinct to dump stone into the low spots and call it level. The soft layer is still soft under the new cap, so the low spot comes back with a thicker layer of rock on top of it. The repair is to scarify the settled area, break it up, get moisture right, and recompact it in proper lifts before you bring it back to grade.
If the settling is localized to one corner or a strip, that is usually a clue about where organics were left or where water is getting in. Fix the water first, or you will be doing this again.
Is pit run a substitute for fill dirt?
Pit run is unscreened material with rock mixed through it. It drains better than screened subsoil and compacts well, and it costs more. On very wet ground it can be worth using for the lower lifts, where the rock content gives you something to work on top of while the site is still soft.
On a normal site that is not fighting water, screened fill dirt is the cheaper way to gain elevation and it does the job. Save the money for the stone on top, where it does more good.
How long should I let a fill pad sit before building?
If the fill was placed and compacted in 6 to 8 inch lifts at reasonable moisture, waiting buys you very little. The compaction already did what time would have done slowly and incompletely. If the fill was dumped and rough graded, waiting does not save you either, because no amount of sitting substitutes for compaction below the surface.
Either way, letting a wet weather cycle pass over the pad is a useful test. Walk it after a heavy rain and look for soft areas, ponding, and edges that moved. Anything you find then is cheap to fix compared to finding it after the posts are set.