Why cheap driveways fail: sub-base, edge restraint and drainage

Most driveway failures have nothing to do with the surface. Blocks sink, tarmac cracks and resin breaks up because of what was, or was not, done underneath: a thin or missing sub-base, no membrane, edges that are not held in, and water with nowhere to go. Those are exactly the parts a cheap quote leaves out, because you cannot see them once the job is finished.

This guide explains what a sound driveway needs, how to check a quote covers it, and why a doorstep offer of "leftover tarmac" should always be refused.

What a driveway is actually made of

A driveway is a layered structure. From the bottom up:

1. Formation. The natural ground, dug down to firm soil below the topsoil and roots.
2. Geotextile membrane. A permeable fabric that stops the stone sub-base being pushed into soft clay and keeps weeds down.
3. Sub-base. Crushed stone, usually MOT Type 1 (or an open-graded Type 3 for permeable designs), laid in layers and compacted with a plate or roller.
4. Bedding or binder layer. Sharp sand for block paving, a binder course of tarmac for tarmac, or a porous base for resin.
5. Surface. The blocks, resin or top course of tarmac that you see.
6. Edge restraint. Kerbs or edging set in concrete around the sides.

Skip or thin any of layers 1 to 4, or leave out 6, and the surface will move.

Sub-base depth

The sub-base carries the weight of the car and spreads it into the ground. For a domestic driveway used by cars, a compacted sub-base of about 150mm is a common minimum on firm ground, and more on soft or clay ground, which is widespread across Birmingham and the Black Country. Paths need less.

The cheap version: 50mm of stone, or none at all, laid straight onto topsoil or an old surface, compacted once. It feels solid on day one. After a wet winter, the wheel tracks sink and the blocks rut.

What to ask: How deep will you dig? How much sub-base, in how many layers, and how will it be compacted? Will you take the topsoil out?

Geotextile membrane

On clay and soft ground, the stone gets pushed into the soil over time and mud pumps up through it. A geotextile membrane on the dug-out formation keeps the two apart. It costs little, which makes leaving it out a telling shortcut.

Edge restraint

Block paving is held together by friction between blocks, which only works if the edges cannot move. Edge kerbs need to be set on and backed with concrete ("haunched"). Without them, the outer blocks creep outwards, joints open and the whole area loosens. Tarmac without edgings crumbles at the sides. Resin needs a firm edge to finish against.

What to ask: What edging will you use, and will it be set in concrete? Edging typically costs £25–£45 per metre, so a quote with no edging line is either leaving it out or hiding it.

Drainage and falls

Water is the main enemy. A drive needs:

• A fall so water runs away from the house, typically around 1 in 60 to 1 in 80.
• Somewhere for the water to go. A lawn, border, channel drain or soakaway, not the house wall, the garage or the neighbour's drive.
• The right level at the house. The finished surface should be at least 150mm below the damp-proof course, and air bricks must not be covered.
• The 5m² rule for front drives. See permeable paving and the 5m² rule.

The cheap version lays the drive flat, or sloping towards the house, with no channel, and water sits in puddles, freezes or runs under the front door. Retro-fitting a channel drain costs £60–£100 per metre and a soakaway £600–£1,200, so it is better to price it in from the start. See drainage and soakaways.

Signs a quote is too cheap

• A single price with no breakdown of digging out, sub-base, membrane, edging and drainage.
• A price well below the ranges below for a new drive on grass.
• No site visit, or a price given over the phone without measuring.
• "We'll lay it over the old one" when the old one is cracked or sunken.
• Pressure to decide today, or a large cash deposit.

Indicative West Midlands prices for a new two-car drive (about 30m²) on grass, including excavation and edgings:

See the driveway cost per m² guide for more.

The "leftover tarmac" doorstep offer

A familiar approach: someone knocks, says they have tarmac left over from a job nearby, and offers to do your drive cheaply, today. Say no. The pattern is well known to Trading Standards:

• The "leftover" material is often poor or not tarmac at all, laid thin with little or no sub-base.
• The price rises once work starts, often with pressure for cash or a trip to the bank.
• The firm cannot be traced afterwards to fix the cracks and puddles.

If you agree to work at your home after an uninvited visit, consumer law generally gives you a 14-day right to cancel, and the trader must give you written cancellation information. If you feel pressured, contact Citizens Advice, which passes reports to Trading Standards, or the police if you feel unsafe.

A genuine firm will visit, measure, give a written quote describing the layers, and leave you time to think. When you use our service, we pass your enquiry to one local specialist whose public liability insurance we have seen, whose identity and trading name we have confirmed, and whose waste carrier registration we have checked where waste leaves site. See how we check firms.

Getting it right

Ask every installer the same questions and compare the answers:

1. How deep will you excavate, and what happens to the spoil?
2. What sub-base, how thick, compacted how?
3. Will you use a membrane?
4. What edging, and is it set in concrete?
5. Which way will the drive fall, and where does the water go?
6. How does it meet the 5m² rule if it is at the front?
7. What guarantee do you give, in writing?

Our pages on tarmac driveways, block paving, resin driveways and turfing and groundworks explain what each job involves.