Drain Rock for Trenches, Drywells and Wall Backfill

Two questions decide this order, and neither of them is how much. The first is whether the stone will be seen or buried, because that settles rounded against angular. The second is how wide the trench is, because drain rock runs from 3/4 inch up to 1-1/2 inch and the coarse end fills a deep trench far faster than it works into a narrow one. Everything else about the material is the same either way: it is washed, the dust and fines are gone, and the space left between the pieces is the product.

Cutting a water route through clay before the first storms arrive

Across the Coast Range valleys, the southern inland basins and much of the valley floor, a year's rain turns up in a few winter storms and atmospheric rivers. It lands on clay that takes water slowly, or on ground with a cemented hardpan a few feet down that stops it moving deeper. The water does not soak away; it sits, or it runs. A trench of washed stone gives it somewhere to collect and a graded route to leave by, which is the whole reason these loads get bought between August and November.

The same logic puts stone behind a retaining wall. Saturated soil pushes hard against the back of a wall, and a column of clean stone with an outlet at the bottom relieves that pressure instead of storing it through the wet months.

Rounded or angular: the choice that decides which load you want

Both varieties are washed and both drain. The difference is what happens under load and under the eye.

Rounded stone looks like it belongs in an exposed swale or an open landscape drain, where the surface is part of the design and nothing heavy sits on top of it. Angular stone wedges together and holds its voids open under the weight of backfill above, which is what you want in a buried trench, behind a wall, or under anything that will later carry traffic. Pick by where the stone ends up rather than by preference, and keep the varieties on the job they were chosen for.

Across a rural lane, beside a garden path, under a new lawn

Three jobs cover most of what leaves on these tickets.

A long rural lane that loses its surface every winter is usually losing it to water crossing the lane rather than falling on it. An interceptor trench cut across the line of flow, filled with angular stone over a perforated pipe and daylighted downhill, takes the water off before it reaches the running surface, and does more for the lane than another load of gravel.

A garden path that floods at one end normally has a low point with nowhere to drain. A French drain run alongside the path, rather than under it, catches water before it reaches the walking surface. Rounded stone suits the exposed stretches, angular for the buried run.

New lawn prep on clay is the third, and the one people skip. Turf laid over ground that holds water gives you a wet lawn, not a green one. A sub-drain line through the low half of the area, backfilled with stone and capped with soil, decides how the lawn behaves for its whole life.

Fabric, pipe, and the silt that shuts a trench in one winter

A drain fails from the top down. Fine soil washes into the stone, fills the voids, and the trench quietly becomes a buried strip of dirt that looks exactly like a drain from above.

Line the trench with a non-woven filter fabric before the stone goes in, lap it generously, and fold it over the top of the stone before the cap goes on. Set perforated pipe at the bottom with a fall towards a real outlet, surround it in stone rather than resting it on soil, and keep a stone layer above it rather than burying it in fill. Where a solid cap is needed, put a few inches of soil or a paving layer over the folded fabric. Where the trench is meant to take surface water, leave the stone exposed and keep soil, mulch and clippings off it.

Set against #67 stone and #4 crushed stone

Going down a size, #67 Stone at 1/4 to 3/4 inch is the easier fill in a narrow trench or tight around pipework, because it flows into the gaps a 1-1/2 inch stone bridges over. Going up, #4 Crushed Stone at 3/4 to 1-1/2 inches holds huge voids and suits deep, high-volume work such as a ditch bottom or a bridging layer on soft ground, but it is awkward to place by hand and leaves gaps too large for fine soil to sit against.

Drain rock sits in the useful middle of that range, which is also why concrete work and drainage work ask for the same washed stone. A clean, graded aggregate with no clay or dust on it is what a concrete mix needs to bond properly, and it is what a trench needs to stay open. The washing is doing the same job in both cases.

Stone for a 70 foot path drain and a lane interceptor

As an example, a French drain beside a garden path, 70 feet long, 18 inches wide and 18 inches deep: 1.5 x 70 gives 105 square feet, and at 1.5 feet deep that is 157.5 cubic feet, which divided by 27 is 5.8 cubic yards. A 4 inch pipe displaces only about 0.2 of a yard over that length, so it barely moves the figure.

The lane interceptor, 22 feet across, 2 feet wide and 2 feet deep: 2 x 22 x 2 gives 88 cubic feet, or 3.3 cubic yards. Together that is 9.1 cubic yards. Washed stone in this family is published on this site at about 2,800 lb per cubic yard, or 1.4 tons per yard, so 9.1 x 1.4 is roughly 12.7 tons. Round to 13 and use the gravel calculator to test other trench widths before you settle.

Ordering to a lot where the trench is already open

An open trench sets its own deadline, so quantity and a delivery date are worth fixing before the digging starts rather than after. Both are chosen here on the product page, and delivery is arranged at checkout from your ZIP code. The truck needs firm, level ground to tip on with nothing overhead, and clean stone tipped onto bare soil picks up the very fines that washing removed, so lay a tarp or drop on the drive. Questions about a narrow or shared access are better raised through the contact page first.