How Deep to Dig for a Driveway? Excellent Guide

How Deep Should a Base Be for a Driveway?

How deep to dig for a driveway is the sum total of driveway thickness and the base thickness. The total thickness of the base (sub-base + base) should be 6” – 8” for asphalt and concrete driveways. Paver driveways need a base of 5” – 6” while a gravel driveway needs a total base thickness of 12”.

Driveway Material	Sub-base Thickness	Base Thickness	Total Thickness
Asphalt		6” – 8”	6” – 8”
Concrete	4” – 6”	2”	6” – 8”
Gravel	6”	6”	12”
Paver	4”	1” – 2”	5” – 6”

The Table above can be used as a general guideline but do keep in mind that the ideal thickness of the base is dictated by several factors as under:

• The local building code specifications
• Soil texture of the subgrade
• Size and quality of the material used in sub-base and base
• The driveway material & thickness
• Expected load (cars or trucks)

Asphalt Driveway

The base should be crushed stone, angular gravel or recycled concrete. For best results lay a 4” thick layer of the base material and compact it. Then lay another 4” thick layer of the base material and compact it.

Concrete Driveway

The sub-base should be several layers of crushed stone, angular gravel or recycled concrete. The size of the crushed stone or angular gravel must increase from top to bottom. 

Gravel Driveway

For best results a gravel driveway should be made of 6” thick compacted gravel sub-base topped with 6” thick compacted gravel base. The surface itself should be another 6” of gravel.

TIP 1: Use geotextile between the subgrade and sub-base. This will prevent migration of gravel from the sub-base to subgrade. 

TIP 2: Use stabilizing plastic paver grid in sub-base and base to improve interlocking and prevent lateral shifts of gravel.

Paver Driveway

Prepare the sub-base using two layers of crushed stone or angular gravel. Each layer should be 2” thick and compacted before the next layer is placed.

The base should be 1” thick layer of bedding sand. For additional strength and stability, precede this layer with a 1” thick compacted layer of # 10 limestone or stone dust.

How Deep to Dig for a Driveway?

You need to decide whether you want your concrete to be level with the surrounding grade, a couple of inches higher or a couple of inches lower. This will need to be factored into how deep you should dig.

How deep to dig for a driveway is the sum total of

1. Concrete Slab Thickness (4” – 6”)
2. Base Thickness (2”)
3. Sub-base Thickness (4” – 6”)

To the above total you will need to add (if the driveway will be lower) or subtract (if the driveway will be higher) the difference in level between the driveway and the adjacent grade.

You may need to dig deeper than the depth calculated above, if the native soil will not meet the basic subgrade soil requirements. Around 4” of poor quality native soil should be excavated and replaced with a better quality soil.

Attributes of a Good Quality Subgrade

• Minimal volume change due to moisture levels and frost
• Strength & Stability
• Compactability
• Drainage Permeability 

NOTE: Laying Geotextile Fabric over the subgrade helps improve drainage and prevents loss of aggregates due to soil movement.

RECOMMENDED PRODUCT

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The Best Geotextile Driveway Fabric for Your Driveway & Patio Base

Geotextile driveway fabric is a supportive layer that is laid between the compacted subgrade and the sub-base aggregates to prevent the migration and loss of the aggregates in to the subgrade. It helps stabilize the ground, permit drainage and prevent weed growth.

Here is the Geotextile Driveway Fabric I recommend.

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How Do You Calculate Excavation Volume?

The excavation volume can be calculated using the following formula:

Excavation Volume (cubic yards) = {Length (ft) X Width (ft) X Depth (in) / 12} / 27

What Machine Is Used for Digging?

The tool or the machine that you must use for excavation and moving the excavated soil will depend on

1. The Excavation Volume
2. Hardness of the existing grade
3. Accessibility

For a DIY project with a small excavation volume and a relatively soft grade you can use simple tools like shovels & wheelbarrows. Of course you will need to put in a fair amount of “sweat equity”.

For medium sized projects you can hire machinery such as:

• Backhoe Loader
• Skid Steer Loader
• Compact or Mini Excavator
• Compactor
• Bulldozer

You can rent earth digging & moving machinery from Home Depot or CAT Rental or other rental agencies in your area. They will rent out for half day, full day or even longer.

For a larger or more complex concrete driveway project you are better off contracting the job to a professional company. They have the expertise, experience and equipment!

Thank you very much for reading this post. I do hope you found it informative and helpful.