How Deep Should a Paver Base Be?

Every paver patio that fails without a drainage problem failed at the base. The pavers themselves are enormously strong and do almost nothing structurally — they spread load into the layer beneath and depend entirely on that layer being flat, compacted and stable. So the question of how deep a paver base should be is really the question of how much load it has to carry and how hard the winter is.

The depths

4 to 6 inches of compacted aggregate for a patio or walkway carrying foot traffic. Six is the safer default and the difference in cost is small.

8 to 12 inches for a driveway carrying vehicles. A car is not a person, and the load spreads through the base at roughly a 45-degree cone — a shallow base simply does not have room to distribute it before it reaches the subgrade.

More in a hard-freeze climate, where frost heave rather than load is the governing case. Ask locally; the number people give you will be larger than either figure above, and they are not padding it.

The paver patio calculator converts a depth into tons of base stone and cubic yards, which is the conversion you need to actually order it — aggregate is calculated by volume and sold by weight.

Get the right material

This is where more jobs go wrong than on depth.

You want dense-graded aggregate — the deliberate blend of stone sizes right down to fines that locks together and compacts into a solid, stable layer. Ask for road base, crusher run, or whatever your local yard calls it, by name.

What you do not want is clean, open-graded stone. It looks similar in a pile, it is what goes in a french drain, and it does the opposite job — the whole point of clean stone is that water and movement pass through it freely, which is precisely wrong under something that must not move.

"Gravel" as a word covers both. Look at the pile before it is dumped, and if it is all one size with no dust in it, it is the wrong material.

Compact in lifts, or you have not compacted

Three inches at a time, plate compactor, passes in both directions.

Dumping six inches and running the compactor over it once compacts the top two inches and leaves four inches of loose material underneath. The surface will feel solid. It will settle over the following year, unevenly, and there is no fixing it from the top.

The rental cost of a plate compactor for a day is trivial next to relaying a patio. It is not an optional tool for this job, and hand-tamping does not substitute for it beyond very small areas.

While you are compacting, build in the slope: an eighth to a quarter inch of fall per foot, away from the house, established in the base and carried through the pavers. Flat patios hold water, and water is what destroys a base. The slope and grade calculator converts between the percent grade on a plan and the inches-per-foot you will actually measure with a level.

One inch of bedding sand. One.

Over the compacted base goes screeded coarse sand, one inch thick, not compacted before the pavers go down.

One inch is the number, not a starting point. The temptation — and it is a strong one, because it saves an hour of base work — is to use bedding sand to smooth out a base that is not quite level. Do not.

Sand is not structural. Where it is thick, pavers settle under load; where it is thin, they do not. The resulting ripple is permanent, highly visible in low raking light, and the only remedy is lifting everything.

Screed to one inch off a flat base. That is the entire technique, and the flatness has to come from the base.

Geotextile fabric, and when it earns its keep

A layer of non-woven geotextile between the subgrade and the base is inexpensive and does one specific job: it stops the base aggregate migrating down into soft subgrade over time.

In sand or well-drained gravel subgrade you can skip it. In clay, do not — clay pumps under repeated loading, and base stone genuinely disappears into it over a few seasons, taking your levels with it.

Edge restraint is not optional

Every edge that is not against a building or a kerb needs restraint: plastic or aluminium edging spiked into the compacted base, sitting tight against the outer face of the perimeter pavers.

Without it the perimeter row creeps outward under traffic. Joints open, the jointing sand washes out, the interlock is lost, and the failure works inward one row at a time. It is a slow, entirely avoidable failure, and the material costs very little relative to the perimeter it protects.

Jointing sand is structural too

After the pavers are down and vibrated into the bedding, sand is swept into the joints and compacted in.

This is not cosmetic. The sand in the joints is what makes an interlocking pavement interlock — it transfers load sideways between units, so a wheel on one paver is carried by a dozen. Joints left empty leave every paver working alone.

Polymeric sand, which binds when wetted, resists washout and weeds far better than plain sand at a few times the price. Coverage runs roughly 40 square feet per 50-pound bag on standard joints.

Getting the quantities right

The base is the expensive part by volume, so the order is worth checking twice. Base and bedding are calculated as volume and bought by weight, converting at roughly 1.4 tons per cubic yard for crushed stone and 1.35 for sand.

Order for the compacted depth you want, not the loose depth. Aggregate loses roughly 15 to 25 percent of its loose volume under proper compaction, so a pile that looks generous when it lands is about right when it is rolled.

For the excavation that comes first, the excavation calculator covers the swell that makes dug soil occupy more space leaving the site than it did in the ground, and how many truckloads that becomes.

For the industry technical specifications on base construction and jointing, the Interlocking Concrete Pavement Institute publishes the detail sheets most professional installers work from.