The specification
The buried half of a patio
ICPI’s published figure for every layer under a patio, walkway or driveway, and a written scope to send with every bid request.
Find a Landscaping Company Paver and base calculator
Written by HyreYard Research Desk Primary-source research and fact checking
The short answer
A paver patio is four layers: compacted subgrade, compacted aggregate base, about 1 inch of bedding sand, then the pavers.
ICPI Tech Spec 2 publishes 4 inches of compacted base as the minimum for a patio on well-drained soil and 6 inches for a driveway, 2 to 4 inches more on cold or wet ground, and a slope of at least 1.5%.
What should you know before anyone digs?
Subgrade, base and bedding decide whether the surface stays flat, and all three are covered the day the job ends.
They assume well-drained soil. Wet clay or a hard freeze calls for more, so a depth should come with a reason tied to your ground.
“Properly compacted base” is not a specification. Inches, a compaction target and a slope are.
Find a landscaping company that will write the base spec
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How thick should the base be?
ICPI sets the minimum compacted aggregate base by what will sit on the surface.
| What sits on top | ICPI minimum compacted base |
|---|---|
| Patio, walkway, foot traffic | 4 inches on well-drained soil. |
| Residential driveway | 6 inches on well-drained soil. A parked car is a different load from a chair. |
| Residential street | 8 to 10 inches, or 6 inches where there is no freeze. |
| Cold, wet or weak soil | Add to the figures above. ICPI: “In colder climates, continually wet or weak soils will require that bases be at least 2 to 4 in. (50 to 100 mm) thicker.” |
ICPI also notes: “Greater thicknesses are often used in regions with numerous freeze-thaw cycles, expansive soils, or very cold climates.” The USDA NRCS Web Soil Survey shows your parcel’s mapped soil and drainage class for free. It is a survey map, not a site investigation.
What are the four layers under a paver patio?
From the bottom up. Each one has a published figure a bid can state.
The native soil left after digging, compacted to 98% of standard Proctor density, ASTM D698 for foot traffic, or to modified Proctor density, ASTM D1557 or AASHTO T180 for vehicles.
Crushed stone placed in 4- to 6-inch lifts, each compacted before the next, to the depth in the table above.
ASTM C33 or CSA A23.1 FA1 concrete sand, screeded to an uncompacted nominal 1 inch. A setting bed, not a leveling layer.
Units about 2⅜ inches thick for foot traffic, held by an edge restraint touching at least 1 inch of each edge paver’s side.
Which shortcuts look identical on day one?
Each of these saves the installer time or material, and none shows in a photograph of the finished job.
| The shortcut | What ICPI says |
|---|---|
| Screenings or stone dust as bedding | “Masonry sand for mortar should never be used for bedding, nor should limestone screenings or stone dust.” These fines can hold water one inch below a surface meant to shed it. |
| Extra sand to fill a low spot | “If there is an uneven base, the bedding sand should not be used to compensate for it. Over time, unevenness in the bedding sand will reflect through to the surface.” |
| The base dumped in one pass | Lifts of 4 to 6 inches, compacted one at a time with 7,000 lbf (31 kN) reversible plate compactors. A single deep pass can leave a firm crust over loose stone. |
| Subgrade left uncompacted | 98% of standard Proctor density, ASTM D698 for foot traffic. A perfect base over loose soil can still settle. |
| No edge restraint | “A minimum of 1 in. (25 mm) vertical restraining surface should be in contact with the side of the paver to adequately restrain it.” Without it, the perimeter joints can open and the pavers spread. |
| A dead-flat surface | “Slopes should be a minimum of 1.5%.” Water that does not run off can run into the joints, the bedding and the base. |
| Patio pavers under a car | ICPI distinguishes units around 2⅜ inches for foot traffic from around 3⅛ inches for streets. |
| Building on frozen ground | “Frozen or saturated sand should not be installed, and frozen material should not be compacted.” |
How is a paver base built, step by step?
The order matters: each layer depends on the one below it being finished.
Buried utilities are marked before anyone digs. The dig depth is base plus bedding plus paver, measured from the finished height.
To 98% of standard Proctor density, ASTM D698 for foot traffic. Fill used to raise the grade is compacted too.
4 to 6 inches at a time, each compacted, up to the specified depth.
At least 1.5%, running away from the house, built into the base rather than the sand.
ASTM C33 or CSA A23.1 FA1 concrete sand at a nominal 1 inch, uncompacted, over a base that is already true.
Pavers laid, the edge restraint fixed around the perimeter, joints filled and the field compacted as the scope states.
Paste this into your request for a quote
Send these twelve lines as written and ask for each to be answered in the proposal, not in conversation. A company that builds to the specification can fill them in quickly.
In inches, and where the spoil goes.
A method and a target. ICPI: 98% of standard Proctor density, ASTM D698 for foot traffic; modified Proctor density, ASTM D1557 or AASHTO T180 for vehicles.
In inches, with the reason for that depth given my soil and climate.
ICPI describes 4- to 6-inch lifts and 7,000 lbf (31 kN) reversible plate compactors.
ICPI: ASTM C33 or CSA A23.1 FA1 concrete sand, nominal 1 inch. Not masonry sand, screenings or stone dust.
The type and how it is fixed, with at least 1 inch of vertical contact.
A percentage and a direction. ICPI’s minimum is 1.5%, away from the house.
In inches, and whether it suits the traffic the surface will carry.
The joint material, and whether the field is compacted after laying.
In writing: no frozen or saturated material placed or compacted.
Who calls 811 before digging, and when.
What it covers, for how long, and what voids it.
The eleven lines of a comparable estimate cover the rest of the bid: drainage, plants, disposal, access and maintenance.
Why does a correct base change the price?
The base is where hours and tonnage go. None of it is visible, which is why it is the easiest line to trim.
| Factor | Why it changes the number |
|---|---|
| Deeper digging | Every inch of base is an inch of soil hauled away. Two more inches under a 200-square-foot patio is about 1.2 cubic yards more to dig and haul (our arithmetic). |
| More aggregate | The same depth again in crushed stone, delivered and spread. |
| Lifts and compaction | Each lift is a separate pass with the plate compactor. Thinner lifts take more passes. |
| Access | Whether a machine reaches the work, or every ton goes through a gate by wheelbarrow. |
HyreYard publishes no price for base work. Loose stone compacts, so order more than the in-place volume: ask the supplier how much for that product. Our gravel calculator takes their figure.
A quote without inches has priced a photograph.
If a proposal names no base depth, no compaction target and no slope, it has not specified the part of the patio that decides whether it stays flat. Ask for all three in writing before you compare totals.
How do you read the answers?
Inches, a percentage and a compaction standard answer the question. “Properly compacted” does not.
If the depth would be quoted anywhere in the country, nobody has looked at your soil.
On a wet yard, a proposal that never mentions water has not scoped it.
A deep bedding course is hiding a base problem.
If it is not in the proposal, assume it is not in the price.
What counts as settlement, measured how, for how long.
Your inquiry
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Questions
How deep should the base under a patio be?
Why does a driveway need a thicker base than a patio?
What is subgrade compaction?
What does “placed in lifts” mean?
Can a patio be built in winter?
Does a patio need a permit?
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This page explains the work so you can read a proposal and judge the company that wrote it.