One of the most common questions Minneapolis St. Paul homeowners ask us at Richfield Blacktop is how thick the layer of the asphalt on their driveway should be. That’s a natural question, but the answer may surprise you. Unlike with concrete, where thickness means strength and weight-resistance, thicker is not necessarily better when it comes to asphalt paving. Far more important is the thickness and compaction of the underlying sub-base. The asphalt paving itself retains flexibility over time, and serves mainly as a waterproof coating over the sub-base, which is actually what bears the weight. Without a properly constructed sub-base, asphalt driveway can quickly lose its integrity and as a result, cracks and sunken spots may appear.
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The Right Thickness of a Minnesota Asphalt Driveway
Driveways and Roads are Different
Asphalt paving is applied with paving machines that apply an even thickness of the asphalt paving material. That application is called a “lift,” by pavers. Ranging from 2 ½” to 3″ thick, each lift is compacted after application by a heavy roller compactor. For heavily-traveled roads, which must bear the constant weight of hundreds of vehicles, including heavy trucks passing over it at high speed, paving is usually applied in two “lifts” of 2 ½”. After paving, the two layers are compacted to a thickness of 4″ to form the final thickness. Busy parking lots, like the ones at supermarkets and big box stores are paved in the same way, with two “lifts.”
Residential driveways, on the other hand, are used only by small numbers of vehicles, traveling at slow speeds. Typically, Richfield Blacktop paves residential driveways with one lift of paving, 3″ thick. That is then compacted to 2 ½” thickness. That, combined with the carefully compacted sub-base, is the ideal thickness to provide maximum life and endurance for a residential driveway. If asphalt is applied too thickly, it won’t be properly compacted, and over time, that can lead to depressions where traffic is frequent.
The Importance of the Asphalt Driveway Sub-Base
Careful installation and compaction of a proper sub-base under your driveway is the key to long life and durability for your driveway. Different soil types require different sub-bases, since the sub-base must be properly compacted and must resist infiltration by the underlying soil.
Where soils are sandy, gravelly, or rocky, they drain well and can be compacted to provide a stable and fast-draining sub-base. In softer soils, like clay or loam, a sub-base of Class 5 materials, which compact well and remain stable, is essential. Sub-bases for residential driveways are typically 4″– 8″ thick. In particularly soft loamy or clay soils, it may be necessary to install a layer of special Geotechnical fabric under the sub-base. This fabric, designed to resist deterioration, prevents the soft soil from infiltrating into the sub-base and loosening it. That helps to keep the sub-base compact and able to bear the weight of vehicles without causing sags in the paving.
Richfield Blacktop – Asphalt Driveway Paver for the Twin Cities
Since 1954, we’ve been building top-quality asphalt driveways for Minnesota homeowners. Richfield Blacktop has learned the techniques and driveway designs that look great and hold up over decades of use. As new technologies have developed in the paving industry, Richfield Blacktop has adopted the best of them to the unique conditions of Minnesota. Wherever your home is in the Minneapolis St. Paul metro area, the paving experts at Richfield Blacktop know the soil conditions and will recommend the ideal driveway design to match conditions and your budget. Contact us today for a free, no-obligation consultation and estimate for your driveway. We’ll help you make the best choices of driveway design and construction for your unique property.
