What is the difference between common fill and select fill?

Common fill is unscreened subsoil with no testing behind it, good for raising grade and filling low spots. Select fill is dug from a specific stratum and has to pass lab tests for plasticity before an engineer will accept it under a slab. Same pit, different standard, different price.

What is select fill dirt good for?

Anything that carries load: house pads, commercial building pads, parking areas, road subgrade and backfill under foundations. Its low-plasticity clay-sand blend compacts tight and stays put when moisture changes. It is the material soils engineers around Houston name in their reports for exactly those uses.

How much is select fill per yard in Houston?

Published Houston-area retail prices in 2026 run from the mid-$20s per cubic yard at the low end to roughly $50 per yard in outlying counties, before or including delivery depending on the seller. Volume jobs price by the truckload and the haul distance, not the retail yard price.

What is the difference between topsoil and select fill?

They are opposites. Topsoil is the organic surface layer that grows grass, and organics are specifically excluded from structural fill because they decompose and settle. Select fill is clean mineral soil that compacts into a stable base. Topsoil goes on top at the end, never underneath a slab.

Why does my builder's spec call for select fill?

Because much of the Houston area sits on expansive clay that swells wet and shrinks dry, and a slab riding those movements cracks. A compacted select fill pad puts a stable, low-plasticity layer between the native clay and the foundation, which is why the soils report requires it.

What Is Select Fill, and Why Do Houston Builders Require It?

Select fill is a low-plasticity mix of sandy clay or clayey sand that engineers require under slabs, building pads and pavement. The name means what it says: material selected from the right stratum of a pit and tested to prove it, unlike common fill dirt, which is whatever came out of the ground. Around Houston, if your plans mention a pad, they almost certainly mention select fill.

We dig it every day at our select fill and dirt sales pits in southeast Fort Bend County, so here is the plain-language version of what the spec sheets mean.

Why do Houston builders require select fill at all?

The Houston region sits on expansive clay. That soil swells when it rains and shrinks when it bakes, and a real Houston geotechnical report will describe native ground with a plasticity index around 18 to 20 as having “moderate potential for shrinking and swelling.” A concrete slab poured straight onto ground like that rides every one of those moisture swings.

The fix is a buffer the weather cannot push around: a pad of low-plasticity select fill, placed in thin layers and compacted hard. It carries the load, drains predictably, and barely moves as moisture changes. That is the whole idea, and it is why the engineer will not trade it for cheaper dirt.

What actually counts as select fill?

There is no single national recipe, but Houston-area specs converge tightly. A private geotechnical report for a Houston commercial site calls for fill with a liquid limit under 35 and a plasticity index between 7 and 20. The City of Tomball’s public works standard defines select backfill the same way: clayey gravel, sand or lean clay with a plasticity index between 7 and 20. TxDOT’s statewide embankment spec caps its Type A granular material at a plasticity index of 15.

Read those numbers as a band. Too much plasticity and the material behaves like the swelling clay you are trying to escape. Too little and it will not bind. The 7 to 20 window is the sweet spot two independent Houston-area authorities landed on separately.

The spec also says what select fill cannot contain: no vegetation, no debris, no chunks bigger than about 4 inches, no contaminated material. Clean mineral soil only.

How is select fill placed and compacted?

Buying the right dirt is half the job. The other half is how it goes down:

Step	What the spec typically requires
Subgrade prep	Scarify the existing ground about 6 inches deep and recompact it first
Lift thickness	Loose layers no more than 8 inches thick
Compaction	At least 95 percent of maximum dry density (ASTM D-698); TxDOT requires 98 percent for its Type A
Moisture	Between optimum and about 4 percent above optimum while compacting
Verification	Density tested lift by lift in the field

Too dry and the material will not bond. Too wet and it pumps under the roller. A pad built to this standard holds its elevation and gives the foundation crew a surface the soils engineer will sign off on. This placement work is its own trade, which is what our site prep and building pads service does start to finish.

Select fill vs the other dirt on the price list

Material	What it is	Where it belongs
Select fill	Tested low-PI sandy clay	Under slabs, pads, pavement, anything structural
Bank sand	Screened sand, PI of 7 or less	Trench backfill, bedding, leveling
Common fill	Untested subsoil	Raising grade, low spots, non-structural volume
Topsoil	Organic growing layer	The top few inches, for grass, never under concrete

Price follows the testing. Published Houston-area retail numbers in 2026 run from about $24 per cubic yard for select fill at a city landscape yard to roughly $50 per yard out in Fort Bend County, with units and delivery terms varying by seller. For what whole truckloads cost and why hauling drives the total, see our Houston fill dirt cost guide.

Where the material comes from matters

Select fill is dug, not manufactured. A pit operator opens the face of the pit, identifies the stratum that passes the tests, and digs that layer selectively. Municipal specs even require delivery tickets naming the source location for off-site fill, because dirt with no known source is dirt an inspector can reject.

That is the practical case for buying from the pit owner. We control which stratum gets loaded at our two Fort Bend County pits, the material rides our own tandem trucks, and volume orders are our normal business. If a builder, engineer or landowner spec is sitting on your desk, call (281) 750-6510 and we will talk through the material and the load count.