Question 1

What is Type 1 sub-base (MOT)?

Accepted Answer

Type 1 sub-base, commonly known as MOT Type 1 or crusher run, is a crushed aggregate mix graded from 40mm down to dust. It compacts extremely well and provides a stable, load-bearing foundation for driveways, patios and paths. It conforms to the Highways Agency Specification for Highway Works (SHW) Clause 803. This Type 1 MOT calculator works out quantities in tonnes and bulk bags.

Question 2

How deep should Type 1 sub-base be for a driveway?

Accepted Answer

For a domestic driveway taking cars, a minimum of 150mm (6 inches) of compacted Type 1 sub-base is recommended. For heavier vehicles or commercial use, increase to 200-300mm. For pedestrian paths and patios, 100mm is usually sufficient. After laying the sub-base, add your surface layer — use our Gravel Calculator for gravel or our Paving Slab Calculator for slabs.

Question 3

How much does Type 1 sub-base weigh?

Accepted Answer

Compacted Type 1 MOT aggregate weighs approximately 2.1 tonnes per cubic metre. Loose (uncompacted) Type 1 is slightly lighter at around 1.8-2.0 tonnes per m³. This sub-base tonnage calculator uses the compacted density of 2.1 t/m³ as this represents what you need after compaction.

Question 4

How many bulk bags of Type 1 do I need?

Accepted Answer

Most UK aggregate suppliers fill a Type 1 bulk bag (jumbo / dumpy bag) to around 800-850kg — roughly 0.8 tonnes, or about 0.5 m³ of loose material. To find the number of bags, divide the tonnage by 0.8 and round up. For example, 6.24 tonnes ÷ 0.8 = 7.8, so you would order 8 bulk bags. Bag weight can vary by about ±5% with moisture content, and bags need mechanical lifting equipment to handle.

Question 5

How do I work out Type 1 for an L-shaped driveway?

Accepted Answer

Break the drive into rectangular sections, run the calculator for each section and add the tonnages. Sub-base volume is additive, so the summed total is exact rather than an approximation, and loose aggregate carries no cutting penalty where sections meet, unlike block paving or slabs. Sections can also take different depths, for example 150mm under the parking area and 100mm under a footpath leg. If ordering in bulk bags, add the tonnage figures together and divide by the bag weight once at the end: each separate run rounds its bag count up, so summing the rounded counts can over-order by a bag.

Question 6

Do I need to compact Type 1 sub-base?

Accepted Answer

Yes — Type 1 must be compacted using a vibrating plate compactor (wacker plate) in layers no thicker than 100mm. For depths over 100mm, compact in multiple layers. Proper compaction is essential for a stable, long-lasting base. The surface should not move under foot when properly compacted.

Question 7

Can I use Type 1 under paving slabs?

Accepted Answer

Yes, Type 1 makes an excellent sub-base for paving slabs. Lay 100-150mm of compacted Type 1, then a 30-50mm mortar bed or sharp sand laying course on top. Use our Paving Slab Calculator to work out slab, sand and cement quantities. Type 1 also works under decking — see our Decking Calculator.

Type 1 Sub-Base Calculator — MOT Quantities for Driveways & Paths

How We Calculate This

The formula

Key assumptions

Frequently Asked Questions

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