Tarmac Driveway Installation: Sub-Base, Binder Course, Surface Course Depths and Edging Requirements

Quick Answer: A standard residential tarmac driveway uses 100–150mm Type 1 granular sub-base, 50mm dense binder course (DBM, 20mm graded), and 25–30mm dense wearing course (6mm or 10mm graded surface course). Total construction depth is typically 175–230mm below finished level. For a SuDS-compliant permeable installation, use porous asphalt to BS EN 13108-7 as the surface course over an open-graded sub-base system.

Summary

Tarmac (correctly called bituminous macadam or asphalt, depending on the mix type) has been the dominant UK driveway material for decades. It's cost-effective, durable when properly constructed, and relatively quick to install compared to block paving. A properly built tarmac driveway should last 20–25 years before major resurfacing is needed, and routine surface maintenance (crack sealing, minor patching) can extend this further.

The UK market uses two main product types: dense macadam (DBM) for sub-layers and wearing courses, and hot rolled asphalt (HRA) for wearing courses — though HRA is less common on residential driveways than on roads. Many domestic installers also use open-graded (porous) asphalt as a SuDS-compliant surface alternative to dense macadam.

The biggest differences between a quality installation and a cheap one are: sub-base depth and compaction, proper edging (without it, the tarmac edge will crumble), and using the correct grade of material for each layer. Thin overlay onto poor sub-base is the most common failure mode — the surface looks fine for a year or two, then cracks and potholes appear where the base has failed.

Key Facts

• Dense macadam (DBM) — Standard UK bituminous material for binder course (20mm graded) and wearing course (6mm or 10mm graded); BS EN 13108-1 product standard
• Hot rolled asphalt (HRA) — Gap-graded mix; used less commonly on residential driveways; better for high-speed road surfaces
• Porous asphalt — Open-graded mix to BS EN 13108-7; SUDS-compliant; requires permeable sub-base system
• Sub-base depth — 100mm Type 1 for standard ground; 150mm on made-up ground or shrinkable clay; 200mm for heavy vehicles
• Binder course — 50mm DBM 20mm graded; laid and compacted hot
• Surface/wearing course — 25–30mm DBM 6mm or 10mm graded (denser texture, smoother finish)
• Compaction temperature — Dense macadam must be compacted while hot; surface temperature should not fall below 80°C before full compaction; do not lay in temperatures below 5°C
• Roller passes — Minimum 3 passes with vibrating roller; tandem roller or plate compactor for small areas near edges; roller should cover the full width in overlapping passes
• Edge treatment — Tarmac edges must be supported by haunched kerbs, proprietary metal or polymer edge restraints, or brickwork; unsupported edges crumble within 1–2 years
• Camber — Fall of minimum 1:80 (1.25%) for drainage; 1:40–1:60 preferred
• Join to road — At the road boundary, new tarmac should be tuck-pointed (keyed) into the existing surface or use an in-situ transition; saw cut the old surface at the join line
• Not a surface treatment — Tarmac overlay on existing surface must account for level changes (threshold, drainage, DPC clearance); minimum 25mm overlay is the practical minimum for longevity
• DPC clearance — Finished surface must be 150mm below damp proof course of adjacent buildings
• NRSWA — If work involves the road or footway, a NRSWA licence is required (see dropped kerb application)

Quick Reference Table

Detailed Guidance

Sub-Base Construction

Sub-base quality determines driveway longevity more than any other factor. A thin surface over a poor sub-base will fail within 2–3 years. A properly prepared sub-base should last the life of the driveway.

Excavation — Dig out topsoil and any soft spots to a firm formation. Typical excavation depth 230–280mm for a standard residential driveway. Probe the formation with a steel rod — if it sinks more than 50mm under hand pressure, the ground is too soft and will need either additional depth of sub-base or ground improvement (cement stabilisation, geogrid reinforcement).

Compaction of formation — Compact the formation with a vibrating plate before placing sub-base. This closes surface voids and identifies any soft spots.

Sub-base placement — Place Type 1 in layers of maximum 150mm, compacting each layer before adding the next. The sub-base must be set to the correct level (finished tarmac surface minus 75–80mm for a standard two-layer tarmac build).

Geotextile — On cohesive or clay soils, lay a woven geotextile between formation and sub-base to prevent mixing and to provide drainage.

Edging

Without edge restraints, tarmac will spread laterally under traffic loading and the unsupported edge will crumble within 1–2 seasons.

Options:

• Precast concrete kerbs (BS EN 1340) haunched in C20 concrete — traditional and robust; typical for driveway edges adjacent to lawn or planted areas
• Proprietary metal edge rail — steel or aluminium angle section hammered into sub-base; quick to install; less visible in finished surface
• Brick soldier course — single course of engineering or facing bricks mortared to the sub-base; attractive, matches house materials, provides edge and visual definition
• Existing kerb/wall — if the driveway runs up to an existing wall or kerb, no additional restraint needed at that boundary

All edging must be installed and any concrete haunching cured before tarmac is laid against it.

Laying Binder Course

The binder course (base course) is 50mm of 20mm graded DBM. It is delivered by lorry in a tipper and either poured directly or moved by wheelbarrow/shovel.

Temperature on delivery — DBM should arrive at 120–160°C. Check with a surface thermometer if uncertain. Material that has cooled below 90°C before laying should not be used — it will not compact properly.

Laying — Rake out to 60–65mm loose depth (it compacts to 50mm). Use a straight edge or screed rails to check depth and level. Lay from one end of the area, working back from a compacted edge.

Compaction — Compact with tandem roller (for larger areas) or plate compactor (for small areas and edges). Make at least 3 passes. The binder course should be dense and non-yielding when tested by walking on it.

Allow to cool — If laying surface course immediately, the binder course should be cool enough that the roller does not leave marks (typically 1–2 hours in normal weather). On hot days, allow to cool fully before surface course, or surface course may sink unevenly into soft binder below.

Laying Surface (Wearing) Course

The surface course (6mm or 10mm graded DBM) is the visible top layer. Quality here matters for appearance and resistance to scuffing.

Material — 6mm graded DBM gives a finer surface texture. 10mm gives slightly coarser texture but is slightly faster to lay and more tolerant of imperfect roller technique. For a high-quality residential finish, 6mm is preferred.

Depth — 25–30mm compacted. Rake to 35mm loose.

Working time — Surface course cools faster than binder because it's thinner. On cool days (<10°C ambient), you may have only 15–20 minutes to lay and compact a batch. Plan batch sizes accordingly.

Roller technique — Tandem roller: work from both edges toward the centre, then make diagonal passes for cross-compaction. On a residential driveway, a 1–2 tonne vibrating roller is typical. A vibrating plate can be used but gives less even compaction. Do not roller the edge too aggressively without edging support — the unsupported edge will push out.

Screed joins — Where one screed meets the next, overlap by 75–100mm and compact the join thoroughly. Poorly joined screeds leave a visible ridge.

Textured and Coloured Tarmac

Standard tarmac is black. Coloured tarmac (red, green, buff) uses pigmented bitumen. The pigment adds cost but not significant performance difference. Colour fades over 3–5 years as the bitumen oxidises — the surface goes from rich colour to grey. Applying a bitumen emulsion seal coat restores colour temporarily.

Tarmac can also be printed or textured (pattern imprinted macadam — PIM) but this is a different product category (see pattern imprinted concrete for comparison with concrete).

Porous Asphalt for SuDS Compliance

Porous asphalt (open-graded asphalt, OGFC — Open-Graded Friction Course) uses a bitumen binder with minimal fine aggregate, leaving air voids of 15–25% by volume. Water drains through the surface layer into the sub-base and then to ground.

For a SUDS-compliant tarmac driveway:

• Surface course: porous asphalt to BS EN 13108-7, 50mm depth
• Sub-base: open-graded Type 3 aggregate or cellular geocomposite (not Type 1 which is too dense)
• Geotextile at formation level to prevent fines migration upward
• Permeable edging or overflow drainage at boundaries

This system satisfies the SuDS requirement under GPDO 2008 and does not require householder planning permission for front driveway installation.

Frequently Asked Questions

How long after laying can a tarmac driveway be used?

Surface course tarmac can be walked on after 2–4 hours. Vehicle use should be avoided for 24–48 hours in warm weather, and up to 72 hours in cold weather. Parking in the same spot repeatedly in the first 2 weeks can cause indentations as the bitumen fully cures.

Can I lay tarmac over existing concrete?

Yes, with a bitumen tack coat (emulsion primer) applied to the concrete first to help adhesion. The concrete must be sound, clean, and level. Check the new finished level won't compromise DPC clearance or threshold levels. Minimum overlay is 75mm (binder + surface) for vehicle use.

Why is my tarmac driveway cracking after 2 years?

Most likely causes: inadequate sub-base depth or compaction, tree roots, or edge failure spreading inward. Alligator (crocodile) cracking typically indicates base failure. Edge cracking indicates insufficient edge restraint. A single transverse crack may indicate thermal movement at a join. Diagnosis and repair options depend on the pattern and location of cracking.

Is tarmac or block paving better for a driveway?

Tarmac: lower initial cost, faster installation, easier to repair (patch), but cannot be made permeable with standard materials. Block paving: higher initial cost, more permeable options, individual blocks can be lifted for access to services, more attractive appearance, but joints can encourage weeds. Both have similar lifespans if properly installed (20–25 years).

Regulations & Standards

• BS EN 13108-1 — Bituminous mixtures; material specifications; Part 1 covers asphalt concrete (including dense macadam equivalents)

• BS EN 13108-7 — Bituminous mixtures; material specifications; Part 7 covers porous asphalt

• New Roads and Street Works Act 1991 (NRSWA) — Required for any work in the public highway; requires relevant Street Works Licence

• Building Regulations Part H — Drainage; relevant for surface water disposal from new driveways

• GPDO 2008 — Permitted development; impermeable tarmac over 5m² on front driveway requires planning permission (see suds regulations driveways)

• The Asphalt Industry Alliance — technical guidance on asphalt products and installation

• Highways England: Manual of Contract Documents for Highway Works — Vol. 7 covers pavement materials; relevant for high-specification work

• HSE: Asphalt and Tarmac — health risks from hot bituminous work

• suds regulations driveways — planning permission for impermeable driveways; permeable porous tarmac as an alternative

• resin bound paving guide — resin bound over porous tarmac as a premium alternative surface

• paving near dpc level — finished level requirements relative to DPC

• driveway gradient requirements — slope and drainage requirements for driveways