Asphalt Driveway Thickness in Madison: Inches of Mix and Stone
Three inches is the floor, four is the safer figure on silty ground, and the stone underneath matters more than either.
The short answer, and why it depends on the ground
For a home driveway around Madison, the Wisconsin Asphalt Pavement Association's 2021 design guide gives three answers depending on the soil: 3 inches of asphalt over 6 to 8 inches of crushed stone where the subgrade is good sand or gravel, 3.5 inches over 6 to 10 inches on medium soils such as loams and silty sands, and 4 inches over 9 to 12 inches on poor soils. The asphalt figure gets the attention, but the stone figure changes more from one class to the next.
Poor, in WAPA's terms, means a subgrade with half or more of its weight in silt and clay, the fraction that passes a No. 200 sieve, along with coarser silts and sandy loams where frost reaching the subgrade is a factor. Several soil series described from Dane County sites begin with loess, wind-blown silt laid over glacial till or outwash. That makes the poor-soil row the realistic starting point for asphalt paving in Madison unless a soil check turns up sand or gravel.
What the soils around Madison say
The USDA's official series descriptions make the point with local examples. Dodge silt loam, whose type location is a Dane County site about four miles east and five miles north of Sun Prairie, has 24 to 39 inches of loess over glacial till and sits on drumlins and moraines. Kegonsa, described from a site about two miles southwest of Middleton, has silt loam and silty clay loam over sandy outwash. Plano, a loess soil mapped across Wisconsin, Illinois, Iowa and Indiana, carries 40 to 60 inches of loess, and its subsoil runs 27 to 35 percent clay with less than 10 percent sand.
All three are well drained as soils go, which is good news for a lawn and misleading for a driveway. Wisconsin's local-roads program lists fine-grained silts and clays as the frost-susceptible soils, and it describes the spring thaw, generally early March to early May, as the season when meltwater trapped above still-frozen ground saturates the base. A driveway on loess has to be built for the week in April when the ground under it is at its softest, not for a dry afternoon in August.
What the City of Madison builds in its own right-of-way
The City's 2026 standard specifications give a useful benchmark because they cover driveways directly. Section 402.3 calls for asphalt driveways and asphalt terrace paving to be built of 3 inches of upper-layer pavement placed in one lift on select fill, using a 4 LT 58-28 S or 5 LT 58-28 S mixture or an approved commercial mix, at a yield of 345 to 360 pounds per square yard. Section 401.2(d) builds crushed aggregate driveways from Gradation No. 2 stone, 1-1/2 inches and smaller, six inches deep unless otherwise specified.
Read those as a floor rather than a target. The terrace section is a short strip crossed at walking speed, and the City's base depth is a default the engineer can change. For the private driveway behind it, which carries the same car over silty soil every day for decades, WAPA's poor-soil section of 4 inches of asphalt over 9 to 12 inches of stone is the more conservative match. Anything thinner than 3 inches falls below both references.
Lifts, mix sizes and why 4 inches goes down in two passes
The mix names in the City's specification follow WisDOT's system. The first number is the aggregate size, 4 for a 12.5-millimeter nominal maximum and 5 for 9.5 millimeters. LT marks a low-traffic design, and the trailing S is the standard binder level. The 58-28 in the middle is the performance grade of the asphalt binder, and under the Superpave system its second number is the lowest pavement temperature the binder is designed for, minus 28 degrees Celsius, or about minus 18 Fahrenheit.
Each mix also has a thickness range. WAPA's guide sets a minimum lift of 1.75 inches for a No. 4 mix and 1.25 inches for a No. 5, and caps a surface layer at 2.5 inches for No. 4 and 2 inches for No. 5. That is why a 4-inch driveway is placed in two lifts, a lower layer and a surface layer, each compacted before the next goes on. The City's terrace specification is the exception worth knowing, since it places its 3 inches in a single lift. Compaction matters as much as thickness: the City asks for 93 percent of maximum density in its upper layers.
The stone underneath, and when to add more
Base thickness does two jobs on silty ground. It spreads wheel loads so the weak subgrade is not overstressed, and it keeps the asphalt above the water that collects at the soil surface during a thaw. WAPA's ranges widen for poor soils, 9 to 12 inches for a driveway against 6 to 8 on good soil, and the upper end fits low spots, clay pockets and places where downspouts or lawns drain toward the pavement. The stone should be placed in compacted lifts and proof-rolled before any asphalt arrives.
Some ground needs more than stone. WAPA's guide says organic soils, and soils with a CBR below 2, should be avoided, removed and replaced, or stabilized, and low areas can hold soils like Wacousta, very poorly drained lake-bed sediments that are frequently ponded. A driveway crossing ground like that needs the soft material dug out before the base goes in. The grading and base repair page covers that work, and the driveway paving page covers the full installation.
Heavier use, and what to ask for in writing
Driveways that carry more than cars need more. HomeGuide's general guidance steps from 2 to 3 inches of asphalt over 6 to 8 inches of base for ordinary use to 3 to 4 inches over an 8-to-10-inch base for heavy vehicles, and WAPA's owner guide warns against parking very heavy loads on a driveway not designed for them. A camper, a boat trailer resting on a jack stand or a regular delivery truck is a reason to build at the top of the local range.
When quotes arrive, compare the sections rather than the totals. A quote that answers the points below in writing can be checked against the WAPA table, the City specification and the soil descriptions in this article; one that gives only a price cannot be checked at all.
- Asphalt thickness after compaction, in inches
- Number of lifts and the mix designation for each
- Base depth, stone gradation and how it will be compacted
- What happens if the proof roll finds soft ground
- How the edges and the grades at the garage and sidewalk will be handled
Planning a new driveway? Ask for a quote built on the right section for the soil.
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Quick Answers
Is 3 inches of asphalt enough for a Madison driveway?
On good sand or gravel, yes: that is WAPA's figure for a home driveway on good soil, and it matches the City's terrace specification. On the silty, loess-derived soils found in Dane County soil descriptions, WAPA's figure rises to 4 inches with 9 to 12 inches of stone beneath. The extra inch and the deeper base cost far less than rebuilding a driveway that cracked over a soft base.
Does a thicker base matter more than thicker asphalt?
On weak soil it usually does. The base spreads each wheel load over a wider area of subgrade and lifts the pavement above water that gathers during a thaw, which is exactly where silty ground fails. Between its good and poor soil classes, WAPA's guide adds 3 to 4 inches of stone at each end of the range against a single added inch of asphalt, which shows where its authors put the emphasis.
Can a driveway be paved in one thick lift to save time?
Not well. WAPA's guide limits how thick a single layer of each mix can be, 3 inches for a lower layer of the 12.5-millimeter No. 4 mix and 2.5 inches for a surface layer, because thick lifts are hard to compact evenly. A 4-inch driveway placed in one pass risks low density near the bottom, which shows up later as rutting and early cracking. Two compacted lifts take a little longer and hold up better.
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