# What goes under interlock: paver base depth, gravel and bedding sand for GTA driveways and patios

URL: https://hotivlandscaping.ca/guides/interlock-base-under-pavers/  
Updated: 2026-10-13  
By: Hotiv Landscaping, Markham, Ontario. Call or text (437) 684-2535.

**Short answer:** A paver base in the GTA is compacted crushed gravel, with about 1 inch of bedding sand and then the pavers on top. CMHA's minimum on well-drained soil is 4 inches under walkways and patios and 6 inches under driveways. Unilock suggests 6 to 10 inches for patios and 10 to 14 for driveways, deeper in newer subdivisions. Use Granular A or clear stone for the base, and never stone dust as bedding.

Most of an interlock driveway or patio is underground. The pavers are usually 2⅜ to 3 inches thick, with roughly an inch of bedding sand under them. Under that is the paver base: a deep layer of crushed gravel, compacted in thin lifts over firm soil.

That base decides whether the surface stays flat. Below are the published depths, what the materials are called at a GTA supplier, and what to ask a contractor before any [interlock installation](https://hotivlandscaping.ca/services/interlock-installation/).

## Key numbers

- CMHA minimum, walkway or patio: 4 in (100 mm) of compacted base
- CMHA minimum, driveway: 6 in (150 mm) of compacted base
- Unilock, driveway on clay: At least 12 in (30 cm)
- Bedding sand or chip: About 1 in, screeded, not pre-compacted
- Minimum slope away from the house: 1.5%, about 3/16 in per foot

## What are the layers under interlock?

A standard sand-set paver surface has four layers, from the bottom up:

| Layer | What it is | Thickness | Job |
|---|---|---|---|
| Subgrade | Native soil, dug past the topsoil and compacted | n/a | Carries everything above it |
| Base | Crushed gravel (Granular A, or clear stone in an open-graded system), compacted in lifts | 4–16 in, see below | Spreads the load, drains, resists frost |
| Bedding | Coarse concrete sand, or small clear chip stone (HPB) | About 1 in, screeded, not pre-compacted | Gives the pavers an even seat |
| Pavers and joints | Concrete pavers with joint sand or polymeric sand | 2⅜ in (60 mm) in CMHA's guide, 3 in in Unilock's homeowner chart | The surface you walk and drive on |

*Image: Cross-section beside a house wall: pavers 2⅜ to 3 inches, about 1 inch of bedding sand, a 4 to 16 inch gravel base in lifts, compacted soil and an edge restraint. Four layers under a sand-set paver surface, sloped away from the house at 1.5% or more*

Edge restraints (plastic, aluminum, steel or concrete) hold the outer rows in place. The surface slopes away from the house.

CMHA (the industry group behind the concrete paver tech notes) gives 1.5% as the minimum slope. That's about 3/16 inch per foot.

## How deep should the paver base be?

Plan on 6 to 10 inches of compacted gravel under a patio or walkway and 10 to 14 inches under a driveway, going by Unilock's figures. The numbers vary with the source and the soil:

| Source and site | Walkway or patio | Driveway |
|---|---|---|
| CMHA minimum, well-drained soil | 4 in (100 mm) | 6 in (150 mm) |
| Unilock, established neighbourhood (10+ years) | 6–8 in | 10 in |
| Unilock, newer subdivision | 8–10 in | 12–14 in |
| Unilock, clay soil (minimum) | 8 in (20 cm) | 12 in (30 cm) |
| Unilock contractor guide | 10–12 in | 14–16 in |

Unilock's reason for the subdivision row is that freshly graded lots are hard to judge, while older neighbourhoods have settled. Clay drains poorly, so it wants the extra depth there as a frost-resistant layer.

CMHA adds that colder climates and wet or weak soils need thicker bases. Treat 4 and 6 inches as a floor.

### How deep is the dig?

Deeper than the base. Unilock's homeowner chart for a driveway on clay adds up like this:

- 14 inches of compacted gravel
- 1 inch of bedding
- 3 inch pavers

That's 18 inches, plus any loose subsoil that comes out. Unilock's contractor guide also suggests digging 6 to 12 inches past the edges to make room for the edge restraint.

*Image: Depth ruler for a driveway on clay: 3 inch pavers, 1 inch of bedding and 14 inches of gravel make an 18 inch dig, running 6 to 12 inches past the edge. A driveway on clay needs an 18 inch dig by Unilock's homeowner figures, wider than the paving*

## Granular A or clear stone: which gravel goes under pavers?

Either works if it's angular crushed stone.

Granular A is the Ontario name for a dense-graded crushed aggregate, defined in the provincial spec OPSS.MUNI 1010 as base material for pavement. It's a mix of stone and fines: everything passes a 26.5 mm sieve, and 2 to 8% passes the finest 75 micron sieve. The fines let it compact into a very tight, firm layer.

> **Good to know:** Yards also sell similar mixes as crusher run or "three-quarter minus". When you order, ask whether the load meets Granular A.

Clear stone has no fines. Unilock's open-graded system uses 3/4 inch clear stone (ASTM No. 57) as the base and a smaller chip (ASTM No. 8) as bedding. It suggests the same build for ordinary, non-permeable paving where it suits the site.

Contractors quoted in that Unilock article say a dense-graded base holds water that then freezes. Unilock says clear stone drains much better and carries the load just as well, but it needs a proper edge restraint.

| | Granular A | Clear stone |
|---|---|---|
| What it is | Crushed stone with fines (2–8% passing 75 µm) | Crushed stone, no fines (3/4 in, ASTM No. 57) |
| Bedding on top | Concrete sand | Small chip (ASTM No. 8) or HPB |
| Drainage | Slower, can hold water | Drains much better |
| Watch for | Water held in the base freezing | Needs a proper edge restraint |

*Image: Two close-up squares of crushed stone: Granular A with mixed-size angular stones and fine dust in every gap, and 3/4 inch clear stone with same-size angular stones and open gaps. Granular A (left) holds fines that pack tight. Clear stone (right) has none, so water drains through*

Unilock's contractor guide says the sharp edges of crushed stone are what make it lock together. It doesn't recommend softer or finer material like limestone screenings or stone dust as a base.

## What goes on top of the gravel: sand, HPB or stone dust?

About 1 inch of coarse bedding, screeded flat and left loose until the pavers go down. CMHA specifies bedding sand that meets ASTM C33 or CSA A23.1, which is concrete sand.

> **Watch out:** CMHA says masonry sand, limestone screenings and stone dust should never be used for bedding under concrete pavers. If a quote lists stone dust or screenings for bedding, ask why.

Unilock's homeowner guide also lists HPB or ASTM No. 9 chip stone in place of sand, paired with a clear stone base.

Keep the bedding thin. CMHA says not to use it to make up for an uneven base, because the dips eventually show through. That's one of the causes covered in our guide on [why interlock sinks and how to fix it](https://hotivlandscaping.ca/guides/fix-sunken-interlock/).

## Do you need landscape fabric under the base?

On clay or soil that stays wet, yes. CMHA lists geotextile as optional, but suggests it in three cases:

- where the soil is saturated part of the year
- where there's freeze and thaw
- over clay and moist silty soils

It keeps soil from working up into the gravel under load, so there's less rutting. CMHA says to turn it up the sides of the dig, lay it without wrinkles and overlap seams by at least 12 inches.

## How does Ontario frost affect the base?

A paver base can't go below the frost line here. For comparison, the Ontario Building Code puts footings for an attached deck 1.2 m (48 inches) down.

Interlock copes instead by being flexible, draining well and sitting on gravel that doesn't heave.

Frost heave happens when water in soils with lots of fine particles, like silt and clay, freezes into ice layers. Clean sand and gravel aren't frost susceptible.

In a spring thaw the ground mostly melts from the top down. The frozen layer below traps the meltwater, and the soaked soil loses bearing strength (Pavement Interactive covers both effects). A deeper, well-compacted base spreads the load over that weak spring soil.

CMHA also says frozen base material shouldn't be installed, and nothing should go over a frozen subgrade. In the GTA that rules out base work in the coldest months.

## How is a paver base built, step by step?

The order is the same for a walkway or a driveway; only the depths change.

1. Call for locates. Ontario Dig Authority (formerly Ontario One Call) says locates are free and required by law before you dig, and asks for at least 5 business days' notice for a single address. Private lines, like a gas line to a barbecue, need a separate private locate.
2. Dig out the topsoil, roots and soft material to the depth you need, plus 6 to 12 inches past the edges.
3. Compact the exposed soil. CMHA calls for at least 98% of standard Proctor density.
4. Lay geotextile if the soil is clay or stays wet.
5. Add the gravel in lifts and compact each one. Unilock's homeowner guide says 3 inch layers. CMHA allows 4 to 6 inch lifts with a heavy reversible plate compactor (7,000 lbf) and thinner ones with a 5,000 lbf machine. Shape the slope into the base, not the sand.
6. Install the edge restraint.
7. Screed about 1 inch of bedding sand or HPB. Don't walk on it or pre-compact it.
8. Lay the pavers, compact them into the bedding, then fill and compact the joints.

Our [polymeric sand guide](https://hotivlandscaping.ca/guides/polymeric-sand-guide/) explains what the binder does, and [how to apply polymeric sand](https://hotivlandscaping.ca/guides/how-to-apply-polymeric-sand/) has the steps.

## How much gravel and sand will you need?

Work it out by volume: area in square feet times depth in feet gives cubic feet, and 27 cubic feet make a cubic yard.

| Job | Area | Layer and depth | Volume |
|---|---|---|---|
| 12 × 20 ft patio | 240 sq ft | Base, 8 in (0.67 ft) | 160 cu ft, about 5.9 cu yd |
| 12 × 20 ft patio | 240 sq ft | Bedding, 1 in (0.083 ft) | 20 cu ft, about 0.75 cu yd |
| Driveway pad | 400 sq ft | Base, 12 in | About 15 cu yd |

> **Good to know:** Gravel loses volume when it's compacted, and the figures above don't allow for that. Ask your supplier how much extra to order.

That's why base depth shows up so clearly in a quote. Our [interlock cost guide](https://hotivlandscaping.ca/guides/interlock-cost-gta/) goes through the rest of the price.

## What are the most common paver base mistakes?

- A patio-depth base under a driveway. It holds up for foot traffic, then ruts in the tire tracks.
- One thick dump of gravel compacted only on top. The bottom of the layer never gets dense.
- Stone dust or masonry sand as bedding, against CMHA's guidance.
- Fixing dips with extra sand instead of more gravel.
- No fabric on wet clay, so soil works up into the base.
- Base work over frozen or soaked ground, or right after heavy rain.
- No slope, or slope toward the house, so water sits on the base.

*Image: Two cross-sections side by side: an 8 to 10 inch gravel base under a patio for foot traffic, and a 12 to 14 inch base under a driveway for car tires. Unilock's base depths for a newer subdivision: a driveway needs about 4 inches more gravel than a patio*

## When should you call a pro?

A small walkway is a fair DIY job if you can rent a plate compactor and move a lot of gravel.

A driveway means trucking away soil and compacting a deep base in lifts over a big area. Mistakes there often show up only after a freeze and thaw, and fixing them means lifting the surface.

When you compare quotes, ask each contractor:

- how deep the base is, and which material
- the lift thickness and the compactor
- whether fabric goes in
- what edge restraint they use
- whether removal and disposal are included

If a quote won't say, ask why.

We put in interlock walkways, patios and driveways across [Markham](https://hotivlandscaping.ca/areas/markham/) and nearby, including [Richmond Hill](https://hotivlandscaping.ca/areas/richmond-hill/) and [Stouffville](https://hotivlandscaping.ca/areas/stouffville/). See our [interlock installation service](https://hotivlandscaping.ca/services/interlock-installation/), call or text [(437) 684-2535](tel:+14376842535), or [text us a photo](sms:+14376842535?&body=Hi%20Hotiv%2C%20I%27d%20like%20a%20quote%20for%20) of the area for a free quote.

## Other questions people ask

### How deep does a paver base need to be?

It depends on the load and the soil. CMHA's minimum on well-drained soil is 4 inches of compacted base under walkways and patios and 6 inches under residential driveways. Unilock's figures for typical sites are deeper: 6 to 10 inches for patios and walkways and 10 to 14 inches for driveways, with at least 8 and 12 inches on clay. Bedding sand and the pavers sit on top of that.

### Do I really need a gravel base for pavers?

Yes, unless it's a stepping-stone path nobody minds re-levelling. The compacted gravel carries the weight and spreads it over the soil, and it drains. Clean gravel doesn't heave with frost the way silt and clay do, which matters through an Ontario winter. Without it, pavers settle unevenly and the joints open up.

### Can I lay pavers directly on dirt?

Not if you want them to stay flat. Topsoil is full of organic matter that rots and settles, and clay holds water and moves with frost. CMHA's construction guide says organic material, roots and debris found in the dig should be removed, and the soil compacted to at least 98% of standard Proctor density before any base goes in. Pavers laid straight on dirt rock, sink and grow weeds in the joints.

### Can you use stone dust under pavers?

CMHA says no. Its construction guide says limestone screenings and stone dust, along with masonry sand, should never be used as bedding under concrete pavers. CMHA's reason is that dust and screenings often don't compact evenly and can stop water draining sideways through the bedding. Use coarse concrete sand meeting ASTM C33 or CSA A23.1, or a small clear chip stone if the base is open-graded.

### What should go under a patio, sand or gravel?

Both, in that order. The thick layer is compacted crushed gravel: Granular A or an open-graded clear stone, laid and compacted in thin lifts. On top goes a thin, even screed of bedding, about 1 inch of coarse concrete sand or HPB chip stone. The sand is only there to seat the pavers. It shouldn't be used to fill dips in the gravel.

## Sources

1. [Concrete Masonry & Hardscapes Association: PAV-TEC-002, Construction of Interlocking Concrete Pavements](https://www.cmha.org/resource/pav-tec-002/)
2. [Unilock: How much base is required for paver installations?](https://unilock.com/construction/how-much-base-is-required-for-paving-stone-installation/)
3. [Unilock: How to install a paver patio base](https://unilock.com/diy/paver-base/)
4. [Unilock Contractors: What is paver base and how much you need](https://contractor.unilock.com/installation/paver-installation/everything-you-need-to-know-about-paver-base-a-complete-guide-to-building-a-strong-foundation/)
5. [Unilock Contractors: Open graded base for paver projects](https://contractor.unilock.com/blog/contractors-turning-open-graded-base-installations/)
6. [City of Toronto: TS 1010, amendment to OPSS.MUNI 1010 aggregates (Granular A and B), September 2023](https://www.toronto.ca/wp-content/uploads/2024/10/8614-ecs-specs-roadas-TS-1010-Sep2023.pdf)
7. [Pavement Interactive: Frost action (frost heave and thaw weakening)](https://pavementinteractive.org/reference-desk/design/design-parameters/frost-action/)
8. [Municipality of Trent Hills: Deck design guide (OBC 9.12.2.2 footing depth)](https://www.trenthills.ca/media/qktbwtu1/trent-hills-deck-design-guide.pdf)
9. [Ontario Dig Authority (formerly Ontario One Call): Locates](https://ontariodigauthority.ca/locates-overview/)

## Related guides

- [Sunken interlock: why pavers sink and how to fix them](https://hotivlandscaping.ca/guides/fix-sunken-interlock/)
- [How much does an interlock driveway cost in the GTA?](https://hotivlandscaping.ca/guides/interlock-cost-gta/)
- [Polymeric sand: what it is, when to replace it, and what affects the cost](https://hotivlandscaping.ca/guides/polymeric-sand-guide/)
- [How to apply polymeric sand (and the mistakes that ruin it)](https://hotivlandscaping.ca/guides/how-to-apply-polymeric-sand/)