How a gravel shed pad base is built

What a gravel pad does

A shed set on bare lawn or on a few concrete blocks settles unevenly, and the floor frame sits in wet soil. Within a few years the doors bind, the floor rots at the low corner, and the shed racks out of square. A gravel pad gives the shed a flat, even base that drains.

Gravel drains water down and away from the floor instead of holding it against the wood. It spreads the weight of the shed over the whole footprint. It is also easy to re-level if it ever settles, which is not true of a concrete slab.

For most prefab sheds and small storage buildings, a gravel pad is what the shed maker recommends. Some manufacturers publish a site prep sheet with required pad size and depth. If yours has one, we build to it.

Sizing and layout

We build the pad 1 foot larger than the shed on every side. A 10 by 12 shed gets a 12 by 14 pad. The extra foot catches rain off the roof edge so it does not dig a trench in the soil next to the walls, and it gives room to walk around the shed and set a ladder.

Placement comes before anything is dug. The pad should sit on the highest practical spot, not in a low corner where water collects. It needs access for the shed delivery, which usually means a clear path about 2 feet wider than the shed and no low branches or wires. And it needs to meet the town's setback from the property lines, which we cover below.

We lay out the corners with stakes and string and check the diagonals so the pad is square. On a sloped yard we set a laser or a string line to find how much the ground falls across the footprint. That number decides how deep to dig on the high side and how tall the frame needs to be on the low side.

Excavation and geotextile

We strip the sod and topsoil from the whole pad area. Topsoil is soft and full of organic matter, and it compresses and settles under a load. The goal is to get down to firm subsoil. On most Rockland and Bergen lots that is clay or glacial till 4 to 8 inches down.

The bottom of the excavation is shaped flat, or with a slight fall toward the downhill side so any water that reaches it runs out. Roots, rocks bigger than a fist, and soft pockets come out. Soft spots get filled with stone and compacted, not with loose soil.

Before any stone goes in, we lay a woven geotextile fabric over the subgrade. The fabric keeps the stone from pushing down into the clay and keeps clay from pumping up into the stone when the ground is wet. Without it, a pad on clay slowly loses stone into the soil and settles. The fabric runs up the inside of the frame at the edges.

Which stone: 3/4 inch clean vs quarry process

There are two stones used for shed pads. 3/4 inch clean crushed stone is angular stone about 3/4 inch in size, washed so there are no fines. Water passes straight through it. Quarry process, also called QP or dense grade, is crushed stone mixed with stone dust. It compacts hard and smooth, but it drains slower.

For most shed pads on clay soil, we use 3/4 inch clean stone for the body of the pad because drainage matters more than a smooth surface. The angular pieces lock together when compacted and hold the shed level. Some installers finish the top inch with quarry process or stone dust for a smoother surface to set skids on. Either works if the base under it drains.

A pad built entirely of quarry process on a wet clay lot can hold water under the shed, because the fines slow drainage. Round pea gravel should not be used for the base at all. It rolls under a load and does not lock together. Materials for this area come from local stone yards and landscape suppliers, and naming the product by size and type avoids getting the wrong stone delivered.

Depth, frame, leveling, and compaction

The stone should be 4 to 6 inches deep after compaction. 4 inches is enough for a small shed on firm ground. We go to 6 inches for larger sheds, heavy contents like a tractor or a workshop, and soft or wet clay. On a sloped yard the low side ends up deeper than that, and the stone goes in and gets compacted in lifts no thicker than about 4 inches at a time.

The frame holds the stone in place and gives a clean edge. We use pressure-treated lumber rated for ground contact, usually 4 by 4 or 4 by 6 timbers, or concrete landscape block. Timbers are pinned at the corners and into the ground with rebar. On a slope, the frame is stacked higher on the downhill side, and timbers are pinned to each other as well as to the ground.

Each lift is compacted with a plate compactor, running over it in both directions until the plate stops leaving marks. The top is screeded level with a straight board resting on the frame, then compacted again. We check level across both directions and on the diagonals. A pad that is flat to within about a quarter inch across its width is ready for the shed.

Compaction is the step people skip when building a pad by hand. Loose stone looks level on day one and settles an inch or more under the shed in the first wet season. The plate compactor is what makes the pad hold.

Drainage around the pad

A gravel pad drains the water that falls on it, but it cannot fix water running onto it from uphill. If the pad sits at the bottom of a slope or in the path of a downspout, the ground around it needs to carry water past it. We shape the lawn so the ground falls away from the pad on all sides, or cut a shallow swale on the uphill side to send water around it.

The stone at the bottom of the pad needs somewhere to drain to. On a flat clay lot, water can collect in the stone like a shallow pan. Grading the subgrade toward the downhill edge, and leaving that edge of the frame open or set with gaps, lets the water run out. On a very wet lot we sometimes run a short piece of perforated pipe from the low corner of the pad to daylight.

Roof water from the shed also needs a plan. A shed with gutters should have its downspout directed away from the pad, not onto it. If the yard has broader water problems, see our drainage and excavation page.

Permits and setbacks in Rockland towns

New York's code rules let a town or village exempt small sheds from needing a building permit. Under 19 NYCRR 1203.3, a local government may exempt one-story detached storage sheds and playhouses of 144 square feet or less on one- and two-family home lots. The word is may. Each town decides whether to adopt that exemption, so a shed that needs no permit in one Rockland town can need one in the next.

A building permit exemption is not a zoning exemption. Towns set how far an accessory structure must be from side and rear lot lines, whether it can sit in a front yard, and how tall it can be, and those rules usually apply to every shed regardless of size. Setbacks vary by zoning district, and corner lots often have extra front-yard limits. Stream-side lots and lots with easements can have additional restrictions.

Before we build a pad, we work from the property survey and check the shed's size and location with the town's building department. For sheds above the exemption size, the town may want a plot plan showing the shed and its distance to the lines. Settling this first avoids building a pad in a spot where the shed cannot legally go. For patio and walkway work at the same time, see our hardscape page.

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