How Thick Should Tarmac Be on a Driveway

When considering a new tarmac driveway, one of the most important factors is the thickness of the surface. Thickness directly affects strength, durability and longevity, and getting it wrong can lead to cracking, sinking or early replacement costs. Many homeowners ask how thick tarmac should be on a driveway, but the answer depends on the type of vehicles using it, the base preparation and the overall design. Understanding these points helps ensure your investment lasts for many years.

Why Thickness Matters

The thickness of tarmac determines how well it can withstand daily use. A surface that is too thin will wear down quickly under the weight of vehicles, while one that is too thick may be unnecessary and increase costs without adding much benefit. The key is to balance cost with performance, making sure the tarmac is deep enough to cope with the loads placed on it. A well-laid tarmac surface with the correct thickness can last between 15 and 20 years with proper maintenance.

Standard Driveway Thickness for Cars

For most domestic driveways that will only take cars and light vans, a tarmac thickness of around 25 to 30 millimetres is common for the surface course, which is the top layer. This sits above a stronger base layer, which is usually much thicker. Together, these layers provide enough strength for regular household use. The top layer gives the smooth finish and weather protection, while the base layer carries the load.

Driveways for Heavier Vehicles

Where driveways need to take heavier vehicles, such as large vans, motorhomes or regular delivery lorries, the thickness needs to be increased. In these cases, the base layer may need to be 100 millimetres or more, with a surface layer of around 40 millimetres. This ensures the tarmac will not crack or deform under pressure. A stronger base with the correct depth is particularly important in homes with clay or unstable soil, where movement in the ground can affect surface stability.

The Importance of the Base

The thickness of the tarmac alone is not the full story. A driveway relies heavily on the strength of the foundation beneath it. Before laying tarmac, a sub-base of crushed stone or hardcore is usually compacted to a depth of 150 to 200 millimetres. This provides a stable platform that prevents sinking and spreads the weight of vehicles evenly. Skipping or reducing the sub-base will shorten the lifespan of the driveway regardless of how thick the tarmac surface is.

Two Layers of Tarmac

Most professional installations use a two-layer approach. The first is the binder course, which is thicker and made with larger aggregate for strength. This layer may be 50 to 60 millimetres deep. On top of that sits the surface course, made with finer aggregate for a smooth finish, usually 25 to 30 millimetres thick. Together, these layers create a driveway that is both durable and attractive. In some cases, particularly where space or cost is limited, only a single layer may be used, but this often results in a weaker driveway.

Cost Implications of Thickness

The thicker the tarmac, the more material is needed, which increases cost. On average, tarmac driveways in the UK cost between £45 and £70 per square metre, depending on thickness, base preparation and access to the site. While it might be tempting to reduce thickness to save money, it usually proves more expensive in the long run if the surface fails early. Investing in the right thickness at the start provides better value over the lifespan of the driveway.

Maintenance and Longevity

When laid at the correct thickness and over a solid base, a tarmac driveway can last two decades with light maintenance. Occasional sealing and timely repairs to small cracks or potholes can help preserve its condition. Thin or poorly laid tarmac surfaces are more prone to damage from frost, standing water and heavy loads. This highlights the importance of not cutting corners on thickness during installation.

Practical Examples

A typical three-car domestic driveway would often have a 150 millimetre sub-base, a 60 millimetre binder course, and a 25 millimetre surface course. This provides enough strength for everyday use while maintaining a neat finish. By contrast, a smaller driveway used only for light cars might get away with a thinner binder course, but the top surface should still be around 25 millimetres to withstand weathering. Commercial or heavy-use driveways require even greater thickness, often designed on a case-by-case basis.

Conclusion

So, how thick should tarmac be on a driveway? For most homes, a surface course of around 25 to 30 millimetres on top of a solid base is enough for cars and light vans. Heavier vehicles will require thicker binder and surface layers supported by a deeper sub-base. The right thickness, combined with proper preparation, ensures a driveway that remains strong, stable and attractive for years. Homeowners should always work with experienced installers who understand local soil conditions and building best practice to achieve the best result.