Choosing the right road base is one of the most important decisions in any road, driveway, or hardstand construction project. The wrong choice can mean rutting, deformation, drainage failure, or expensive rework, sometimes years after the road has been opened to traffic.
For NSW civil projects, the choice usually comes down to three options: TfNSW-specified DGB20 (dense graded base), TfNSW-specified DGS40 (dense graded subbase), or an unspecified road base alternative. Each has a clear best use, and a clear scenario where it is the wrong product.
This guide explains what each road base is, where it belongs in a road pavement, when to use it, and how to choose between them based on your project’s traffic loading, specification requirements, and budget. For background on how these products fit into the broader road structure, see our companion guide on how aggregates are used in road construction.
The Three Road Base Options at a Glance
The table below summarises the three products, where each sits in a pavement, and what each is best suited for.
| Product | Layer | Specification | Best for |
| DGB20 | Base course | TfNSW-spec dense graded base (20mm) | Council roads, government and major commercial pavements |
| DGS40 | Subbase | TfNSW-spec dense graded subbase (40mm) | Load distribution layer under DGB20 on TfNSW projects |
| 20mm unspec road base | Base course | No formal TfNSW certification | Driveways, farm roads, private hardstands |
| 40mm unspec road base | Subbase | No formal TfNSW certification | Lower-cost subbase where TfNSW spec is not required |
DGB20: The Standard for NSW Road Base
DGB20 is a 20mm dense graded base material specified by Transport for NSW (TfNSW, formerly RMS). It is the standard base course for sealed road pavements across NSW and is required on government road projects, council infrastructure, and most commercial developments.
Why dense grading matters
The “dense graded” part of the name is the key to how it performs. DGB20 contains a carefully blended mix of particle sizes, from 20mm crushed rock down to fines, chosen so that the smaller particles fill the voids between larger ones. The result is a layer that compacts to high density with minimal voids, giving the load-bearing capacity needed for sealed pavements under repeated traffic loading.
That dense, low-void structure does two critical jobs. It distributes axle loads efficiently across the layer, reducing stress on the subbase and subgrade below. And it resists deformation under cyclic loading from cars, trucks, and heavy vehicles passing over the same wheel paths thousands of times a day. Open-graded or single-sized materials simply cannot do either job at the same level of performance.
When to choose DGB20
- Any TfNSW-funded road or maintenance project. DGB20 to specification is required.
- Council roads. Most NSW councils require TfNSW-spec DGB20 for their road maintenance and renewal programs.
- Major commercial pavements. Truck parks, distribution centres, industrial hardstands carrying heavy axle loads.
- Sealed pavements generally. Any project where the surface will carry asphalt or sprayed seal, since the cost premium is small over the life of a sealed road.
- Any project where test certificates are required for compliance reporting.
DGB20 specifications you should know
DGB20 must meet TfNSW specification 3051 for particle size distribution, plasticity index, and CBR (California Bearing Ratio) strength. Test certificates are available on request when supplied from our Merriwa quarry. Where a project has additional specification requirements or a council-specific addendum, confirm these against the current TfNSW documents before ordering, since specifications are revised periodically.
DGS40: The Subbase Beneath DGB20
DGS40 is a 40mm dense graded subbase material, also TfNSW-specified. It sits beneath the base course (DGB20) and above the formation layer. Its role is to distribute traffic loads over a wider area, reducing the stress on the subgrade and protecting the base course above.
Compared with DGB20, DGS40 is coarser. The larger 40mm top size means better drainage and a lower cost per cubic metre. It is a load-distribution layer, not a load-bearing surface, which is why it sits below the base course rather than above it. Skipping the subbase or substituting fill material for DGS40 is a common cause of premature pavement failure on projects where budget pressure leads to corner-cutting on the layer beneath the visible work.
When to choose DGS40
- As the subbase layer on TfNSW-spec roads, paired with DGB20 above and the formation below.
- When drainage matters. The coarser gradation passes water more freely than DGB20, helping protect the base course above and the subgrade below from moisture damage.
- To reduce the depth of the more expensive DGB20. A thicker DGS40 subbase can let you reduce the DGB20 base course thickness while still meeting load capacity, often at lower total cost.
- On weaker subgrades where additional load distribution from a robust subbase layer protects the base course from differential settlement.
Unspec Road Base: When You Do Not Need TfNSW Certification
20mm and 40mm unspec road base are crushed rock products with similar gradation to DGB20 and DGS40, but without the formal TfNSW certification process. They cost less, compact well, and perform comparably for many applications. They simply do not carry the test paperwork required for government and council projects.
“Unspec” does not mean low quality. It means the material is supplied without the formal testing regime and documentation trail that TfNSW specification requires. The crushed rock itself can come from the same source as the certified product, processed through the same crusher and screens. The difference is in the paperwork, not the rock.
When unspec road base is the right choice
- Residential driveways. Most driveways carry car loads and occasional delivery trucks. 20mm unspec road base compacts to a durable, low-cost driveway base.
- Farm and rural roads. On private land where formal specifications are not required, unspec is a much cheaper option for the same compaction behaviour.
- Private hardstands and parking areas where the surface is not subject to heavy commercial traffic.
- Subbase under lower-traffic asphalt, where 40mm unspec performs the same role as DGS40 at a lower cost.
When NOT to use unspec road base
Any project that will be audited, certified, or handed over to a council or government body. The lack of test paperwork is usually a deal-breaker, even if the material would have passed the spec test had it been carried out. Substituting unspec on a project that calls for DGB20 to save cost can result in rejected loads, rework, or contractual disputes that dwarf the original supply saving.
How to Choose Between Them: A Decision Checklist
Use this short checklist when specifying road base for your next project.
- Is this a TfNSW, council, or government project? Yes, then DGB20 and DGS40 (no exceptions). No, continue.
- Will the road carry regular heavy commercial traffic (trucks, B-doubles)? Yes, then DGB20 and DGS40, even if unspec would technically pass.
- Will the surface be sealed (asphalt or sprayed seal)? Yes, then strongly recommend DGB20 as the base course. The cost difference is small over the life of a sealed road.
- Is this a private driveway, farm road, or hardstand? Yes, then 20mm unspec road base is almost always the right call.
- Are test certificates required for the contract? Yes, then DGB20 and DGS40 only.
- Budget-constrained but want better-than-fill quality? Then 40mm unspec road base is a strong middle ground for non-spec subbase work.
Layer Thicknesses and Compaction
Regardless of which road base you choose, getting the layer thickness and compaction right is what makes the road perform. Some general guidance for NSW road construction:
- DGB20 base course: typically 100 to 200mm thick, compacted in single lifts to 95 to 98 percent of maximum dry density.
- DGS40 subbase: typically 150 to 300mm thick, compacted in lifts of no more than 150mm at a time.
- Unspec road base (driveways): typically 100 to 150mm thick, compacted with a vibrating plate or small roller.
For deeper pavement designs or projects with weak subgrades, a Select Material Zone (SMZ) of 65mm minus crushed rock typically sits below the subbase to provide a uniform working platform. The full road construction product range includes 65mm minus select fill alongside the base and subbase products discussed here. For exact layer thicknesses on any project carrying traffic loads beyond residential, engage a pavement design engineer who will specify thicknesses based on a CBR analysis of the subgrade.
Cost: How the Three Products Compare
Pricing varies by quantity, delivery distance, and current quarry stocks, but the general ranking is consistent.
- DGB20 is the most expensive per tonne. The test certification, finer gradation control, and consistent quality drive the price.
- DGS40 sits between DGB20 and unspec. It carries the TfNSW certification but uses a coarser, less production-intensive gradation.
- Unspec road base is the lowest-cost option in either 20mm or 40mm sizes.
For most non-government projects, the cost difference between unspec and TfNSW-spec products can be 15 to 30 percent, a meaningful saving when supplying a large private project, but not enough to justify using unspec on a TfNSW-funded road. The whole-of-life cost picture also matters: a slightly cheaper base course that fails prematurely costs far more to repair than the saving on initial supply.
Sourcing Road Base from Hunter Blue Metal
Hunter Blue Metal stocks DGB20, DGS40, 20mm and 40mm unspec road base, and 65mm minus formation fill at our Merriwa quarry. We supply council road programs, government projects, civil contractors, farms, and private builds across the Hunter Valley, Newcastle, and the broader NSW region. Browse the full road construction product range for specifications and bulk supply.
For projects that also need surfacing aggregates, crusher dust, or manufactured sand, our aggregate range and sand and dust products can be coordinated on a single delivery schedule with road base. For a procurement-focused look at how to package a complete road supply order, see our buyer’s guide to road construction supplies.
We supply civil, construction, and agricultural projects of all sizes, with bulk delivery next-day for most jobs. Single tipper loads of around 17 tonne, trailer combinations, and B-doubles are available depending on site access.
Frequently Asked Questions
What is the difference between DGB and DGS road base?
DGB (Dense Graded Base) is a 20mm product used as the base course layer directly beneath the road surface. DGS (Dense Graded Subbase) is a coarser 40mm product used as the subbase layer beneath the base course. Both meet TfNSW specifications but serve different structural roles. Most properly designed road projects use both layers: DGS40 below, DGB20 above.
Can I use unspec road base on a council road?
No. Council and TfNSW projects require TfNSW-specified DGB20 base course with documented test certificates. Unspec road base does not carry the certification required for handover to council ownership or government audit, even if the material itself might pass the same testing if it were carried out.
What road base is best for a residential driveway?
For most residential driveways, 20mm unspec road base is the best balance of cost and performance. Lay 100 to 150mm thick, compact with a vibrating plate, and finish with crusher dust or a sealed surface if desired. DGB20 will perform marginally better but the cost premium is rarely worth it for residential use.
How thick should DGB20 be?
For most council and commercial pavements, DGB20 is laid 100 to 200mm thick depending on design traffic loading. Heavier-trafficked roads use thicker base course; lighter local roads can use the lower end of the range. The pavement design engineer specifies the exact thickness based on a CBR analysis of the subgrade.
Can you supply test certificates for TfNSW-spec products?
Yes. DGB20 and DGS40 supplied from our Merriwa quarry come with test certification on request, covering particle size distribution, plasticity index, and CBR strength to meet TfNSW spec 3051. Talk to our team when ordering if you need certificates delivered with each load.
Get a Quote on Road Base for Your Project
Whether you are laying a council road, sealing a commercial car park, or building a driveway on your property, choosing the right road base is the foundation of a road that lasts. Our team works with civil contractors, council officers, builders, and property owners across the Hunter Valley to specify and supply the right road base on schedule.
Call 1300 150 777 or visit our road construction product page to discuss your project, request a quote, and arrange next-day delivery across the Hunter Valley.
