Driveway Sub-Base: How Much MOT Type 1 Do You Need and How Deep?

A driveway takes far more punishment than a patio. A car's weight is concentrated on four small patches, it turns, it brakes and it sits in the same place every night. Whatever you put on top, from block paving to tarmac to gravel, the sub-base underneath does the heavy lifting. Here is how to work out how much MOT Type 1 you need and how deep to lay it.

How deep should a driveway sub-base be?

For a domestic driveway used by cars on firm ground, a compacted sub-base of around 150mm is the figure most commonly recommended. Some situations call for more:

• Soft or clay ground often needs a deeper base, and sometimes a geotextile membrane to stop the stone sinking into the soil.
• Heavier vehicles such as vans, motorhomes or regular deliveries need a more substantial base.
• Your surfacing choice matters. Block paving, resin, tarmac and gravel each have their own recommended build-up, so check the manufacturer's or installer's specification before you dig.

If you are not sure, ask your installer, or call us on 03330 908479. It is much cheaper to dig a little deeper at the start than to repair a rutted drive later.

Working out how much MOT Type 1

The method is the same as for any sub-base:

1. Area in m² = length × width.
2. Finished volume in m³ = area × depth in metres (150mm = 0.15m).
3. Add 20 to 30% for compaction, settling and uneven ground. We use 25% in the examples below.
4. Multiply by about 1.7 tonnes per m³, a typical loose weight for MOT Type 1.
5. Divide by 0.8 to get the number of 800kg bulk bags, and round up.

Worked example: a 6m × 3m single driveway

• Area: 6 × 3 = 18m²
• Finished volume at 150mm: 18 × 0.15 = 2.7m³
• With a 25% allowance: 2.7 × 1.25 = 3.375m³
• Weight: 3.375 × 1.7 = about 5.7 tonnes
• Bulk bags: 5.7 ÷ 0.8 = 7.2, so 8 bags

At £48.75 ex VAT per MOT Type 1 bulk bag at the time of writing, 8 bags come to £390 ex VAT.

Worked example: a 6m × 5m double driveway

• Area: 30m², finished volume 4.5m³, with allowance 5.6m³
• Weight: about 9.6 tonnes
• Bulk bags: 12 bags, which is £585 ex VAT and over our £500 ex VAT free-delivery threshold

Laying a driveway sub-base

1. Mark out and excavate. Dig to the full depth of sub-base plus bedding plus surface, allowing for the finished level to sit below any damp-proof course and to fall away from the house.
2. Compact the formation. Firm up the exposed ground. Replace any soft spots with stone.
3. Lay a membrane if needed on soft or clay ground.
4. Spread and compact in layers. A 150mm finished depth is usually built in two layers, compacting each with a plate compactor suitable for the thickness. Hiring a heavier machine for a drive is worth it.
5. Check levels and falls as you go. Water should run off or drain through, not pool against the house.
6. Add the bedding and surface to your installer's specification.

Hardcore or MOT Type 1?

Some installers use a coarser hardcore lower layer and cap it with MOT Type 1 to get a tight, even surface. We sell both: MOT Type 1 sub-base bulk bag (800kg) and hardcore / crusher run bulk bag. Whichever you choose, plan the depth of each layer first so you order the right amounts.

Planning permission and drainage

In England, paving over more than 5 square metres of a front garden with a hard, non-porous surface generally needs planning permission, unless the rainwater drains to a lawn or border or you use a permeable surface. The rules can vary, for example in conservation areas or on listed buildings, so check with your local planning authority. The government guidance on permeable surfacing of front gardens explains the options. If you are using a permeable surface, your build-up may call for open, free-draining stone instead of MOT Type 1, so follow the specification for your system.

Before the delivery arrives

• Bulk bags are lifted off the lorry with a truck-mounted forklift, so you need a firm, level spot the driver can reach safely. Think about where they will go before the excavation is open.
• Someone must be there to receive the delivery. We will call you to arrange a day.
• Keep the bags clear of where you need to dig, so you are not moving them twice.

Frequently asked questions

How many tonnes of MOT Type 1 do I need for a driveway?

As a rough guide, a 150mm base needs around 0.32 tonnes per m² with a 25% allowance, so 18m² needs about 5.7 tonnes. Work it out for your own measurements and round up to whole bags.

Is 100mm enough for a driveway?

For a lightly used drive on firm ground it may be, but 150mm is the more common recommendation for cars. Ask your installer for the specification that suits your ground and surfacing.

Can I drive on MOT Type 1?

Compacted MOT Type 1 is a sub-base, so it will carry light construction traffic, but it is not a finished surface. Rain will wash out the fines and ruts will form if you leave it exposed for long.

Do I need to compact it?

Yes. Compaction is what turns loose stone into a stable base. A plate compactor can be hired locally and a driveway needs a decent-sized machine.

Should I choose gravel for the top?

It is a popular, permeable option. See our gravel driveway guide for how much you need.

Ordering and delivery

You can browse the full range in our cement and aggregates collection. Bulk bags are sold at approximately 800kg each (the packed weight can be up to 850kg depending on moisture), and most sands and gravels are also available in 20 to 25kg trade packs for small jobs. Prices on our website are shown excluding VAT, and VAT is added at checkout.

We deliver to addresses in mainland England only; we do not currently deliver to Wales, Scotland, Northern Ireland or the islands. Timber, aggregates and cement have a minimum order of £250 ex VAT, and delivery is £25 ex VAT on orders under £500 ex VAT and free over £500 ex VAT. Bulk bags are delivered by Moffett lorry (truck-mounted forklift) and offloaded at your site, so someone must be there to receive them and you will need a firm, level area with suitable access. We do not offer next-day delivery. Our shipping policy has the full details, or call us on 03330 908479 or email sales@insulationwarehousedirect.co.uk if you would like a hand working out your order.

The quantities in this guide are estimates. Ground levels, how well the material is compacted and how wet it is all change what you need, and densities vary between quarries, so check the amount with your installer or the manufacturer's guidance before you order. Prices and pack sizes are correct at the time of writing.

Working out quantities? See our MOT Type 1 sub-base guide: how much do I need? or go straight to our aggregates calculator.