Fill dirt vs topsoil: which one do you actually need?

Birmingham Dirt. Updated October 7, 2026.

The question comes up on almost every quote request. The short answer: fill dirt is for building, topsoil is for growing. The longer answer decides whether your lawn comes in or your shed pad sinks.

What fill dirt is

Fill dirt is subsoil, the layer under the dark top layer. It is what comes out of a basement, a footing or a road cut. Around Birmingham it is mostly red clay, with chert gravel mixed in on the ridges. It has almost no organic matter, and that is the point: organic matter rots and settles, and fill is not supposed to settle.

You buy fill to:

• Raise a low spot that holds water
• Build a pad for a shed, pool, driveway or slab
• Backfill a hole, a trench, a stump or an old pool
• Fill behind a retaining wall or a new foundation
• Bring a sloped lot closer to level before anything else happens

It comes three ways. Unscreened fill is straight off the job, clay and clods and the odd rock, and it is the cheapest dirt there is. Screened fill has been run through a mesh so it spreads and compacts evenly. Clay fill is specifically red clay, which packs hardest and sheds water, and is what you want under anything with weight on it.

Grass will not grow in fill. Not well, not for long. Clay fill dries into something close to brick in July.

What topsoil is

Topsoil is the top few inches of ground where plants have been living and dying for a long time. It is darker, looser and full of organic matter. It holds water without going to soup, and roots can push through it.

Most lots around Birmingham were scraped to clay when the house was built, which is why so many lawns here are thin and why bought topsoil is a thing. Bought topsoil is usually screened, with rocks and roots pulled out so it spreads smooth. A garden mix is topsoil blended with compost, for raised beds and planting where you want more than grass to grow.

You buy topsoil to:

• Start a lawn from seed or sod
• Level low spots in a yard you want to keep mowing
• Fill raised beds and planting areas
• Top-dress a thin lawn
• Finish over fill before seeding

Topsoil is not for building on. It settles, it holds water, and a slab or wall on it will move.

The prices

Fill dirt in the Birmingham area runs about $8 to $20 a yard, and a tandem load of around 12 yards usually lands between $150 and $350 delivered. Screened topsoil runs $25 to $50 a yard, so the same load is $300 to $650. Garden mix costs more again. Most of the delivered price is the truck, which is why a half load costs nearly what a full one does.

Those are typical ranges, not quotes. Distance from the yard, access and the time of year move them.

Most jobs need both

The usual order is fill first, topsoil on top. A low spot in a lawn gets fill to within four inches of grade, then four inches of topsoil, then seed. A new house lot that was scraped to clay gets graded with fill so water runs away from the house, then topsoil, then sod. A raised bed sits on whatever is there and gets filled with garden mix.

Rough up the clay before the topsoil goes on so the two layers knit together instead of sliding apart. And do not skimp on the topsoil depth. Three inches over red clay dries out in the first hot week. Four is the minimum, six is better.

How much topsoil for a lawn

One cubic yard covers 81 square feet at four inches deep, or 54 square feet at six. A 2,000 square foot front lawn at four inches needs about 25 yards, which is two tandem loads. Measure the lawn in feet, multiply length by width by depth in inches, and divide by 324. The calculator does this and adds the settling.

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