What is MOT Type 1 sub-base?

MOT Type 1 is a crushed stone aggregate graded from about 40 mm down to dust — formally a 0/31.5 mm unbound mixture — defined in the UK Specification for Highway Works, Series 800, Clause 803 (and BS EN 13285). The blend of sizes interlocks and compacts to a dense, load-bearing layer, which is why it is the default sub-base under driveways, patios and paths. It is made from crushed limestone, granite, or recycled crushed concrete conforming to BS EN 13242. (The 'MOT' name comes from the old Ministry of Transport.)

What is the difference between Type 1, Type 2 and Type 3 sub-base?

Type 1 (Clause 803) contains fines that fill the voids, giving maximum strength but little drainage. Type 2 is similar but allows more fines and a smaller top size — cheaper and fine for lightly loaded paths, but weaker. Type 3 (Clause 805) is a reduced-fines, open-graded 'permeable' sub-base — the dust is removed so water drains through it, making it the choice for SuDS-compliant permeable paving.

How deep should the sub-base be for a patio or driveway?

For a foot-traffic patio or path, 100 mm of compacted sub-base is normal. For a domestic driveway carrying cars, lay 150 mm. Soft, wet or clay ground may need 200 mm or more plus a geotextile membrane. Always compact in lifts of 75–100 mm or less — a deep layer laid in one go will never reach full density.

How do I calculate sub-base tonnage?

Work out finished volume as area (m²) × compacted depth (m). MOT Type 1 is delivered loose and compacts by about 30%, so order roughly 1.3× that volume and convert to tonnes at a loose density of about 1.85 t/m³. As a check, one tonne covers about 5 m² at 100 mm or 3.5 m² at 150 mm compacted. The calculator on this page does this automatically once you enter your area and depth.

Does sub-base need a geotextile membrane?

A woven geotextile membrane between the subgrade and the sub-base stops the stone punching into soft ground and prevents weeds and silt migrating up into the layer. It is strongly recommended on clay or wet ground and is cheap insurance on any driveway. On very soft ground a geogrid can be added to bridge weak spots.

Do I need planning permission for a new driveway?

In England, since 2008, a front driveway over 5 m² that uses an impermeable surface draining to the road needs planning permission. A permeable surface (such as permeable block paving on a Type 3 sub-base), or one that drains to a lawn or border, is permitted development. Wales has equivalent rules. Always check current SuDS guidance for your area.

How much should I compact MOT Type 1?

Lay it slightly damp and compact each 75–100 mm lift with a vibrating plate (wacker plate) for paths and patios, or a vibrating roller for driveways. Make several passes until the surface stops moving and rings solid. Light watering helps the fines bind. Proper compaction is what stops future sinking and rutting.

Sub-Base & MOT Type 1 Guide — Depths, Specs & Tonnage (UK)

What is a sub-base?

A sub-base is the compacted layer of crushed stone that sits between the ground (the subgrade) and your paving, sand or concrete. It spreads vehicle and foot loads, stops the surface sinking and provides a stable, free-draining platform. In the UK the default specification is MOT Type 1 — the "MOT" stands for the old Ministry of Transport, which originally specified this aggregate for highway construction. It is a graded aggregate from about 40 mm down to dust (formally a 0/31.5 mm unbound mixture) defined in the Specification for Highway Works, Series 800, Clause 803 ("Type 1 unbound mixtures"). The mix of particle sizes locks together under compaction to form a dense, load-bearing base. Material is typically crushed limestone or granite, or recycled crushed concrete, conforming to the mixture standard BS EN 13285 with aggregate to BS EN 13242.

Type 1 vs Type 2 vs Type 3 (permeable)

Type 1 includes fines that lock the stone together for maximum strength but limited drainage. Type 2 allows more fines and a smaller top size — cheaper and acceptable for lightly loaded paths, but weaker. Type 3 is a reduced-fines, open-graded permeable sub-base (Clause 805) used where SuDS compliance requires water to drain through the build-up rather than run off to the road.

Feature	Type 1	Type 3 (permeable)
Spec (SHW Series 800)	Clause 803	Clause 805
Grading	0/31.5 mm (to dust)	0/40 mm (open-graded)
Max fines (<0.063 mm)	≤9% (UF9)	≤5% (UF5)
Drainage	Low	High (permeable)
Load capacity	Highest	Good
Best for	Driveways, heavy load	SuDS / permeable paving

Standard sub-base depths

Use	Compacted depth	Notes
Path / foot traffic	100 mm	Pedestrian only
Patio	100–150 mm	Furniture, occasional loads
Domestic driveway	150 mm	Cars and light vans
Soft / clay subgrade	200 mm+	Add membrane / geogrid

Depths are compacted thicknesses. Order loose material to suit, then compact down to these figures. On poor subgrades (low CBR), increase the depth or add a geogrid rather than relying on the surface course for strength.

How to lay and compact MOT Type 1

A landscaper compacting freshly laid grey MOT Type 1 sub-base on a domestic driveway with a yellow plate compactor — Compact in lifts of 75–100 mm with a vibrating plate (paths/patios) or roller (driveways).

Excavate to allow for the sub-base depth plus your surface layers — typically 150–250 mm for a driveway.
Roll a woven geotextile membrane over the subgrade, lapping joints by about 300 mm.
Tip and rake MOT Type 1 in lifts of 75–100 mm, keeping it slightly damp so the fines bind.
Compact each lift with a vibrating plate or roller until it stops moving and rings solid.
Check falls and levels (roughly 1:60–1:80 for drainage) before laying the surface course.

Watch: laying a sub-base step by step

Video: a practical walkthrough of excavating, membrane and compacting a sub-base.

How to calculate sub-base tonnage

Work out your finished volume as area (m²) × compacted depth (m). MOT Type 1 arrives loose and compacts by roughly 30%, so order about 1.3× that volume, then convert to tonnes at a loose density of about 1.85 t/m³. As a quick check, one tonne covers roughly 5 m² at 100 mm or 3.5 m² at 150 mm compacted.

Worked example — single driveway

5 m × 6 m = 30 m² at 150 mm (0.15 m) = 4.5 m³ finished. Allow ~30% for compaction → ~5.85 m³ loose to order. 5.85 × 1.85 ≈ 10.8 tonnes of MOT Type 1.

The MOT Type 1 calculator does all of this from your area and depth — including bulk-bag and loose-tipped estimates.

Common mistakes to avoid

• Laying the full depth in one go — it never compacts properly. Work in 75–100 mm lifts.
• Skipping the membrane on clay — the stone sinks and the surface fails within a season.
• Compacting bone-dry material — a light watering helps the fines bind.
• Forgetting falls — build in a 1:60–1:80 slope so water runs off, not into the house.
• Using Type 1 under permeable paving — use Type 3 where SuDS drainage is required.

Frequently asked questions

What is MOT Type 1 sub-base?: MOT Type 1 is a crushed stone aggregate graded from about 40 mm down to dust — formally a 0/31.5 mm unbound mixture — defined in the UK Specification for Highway Works, Series 800, Clause 803 (and BS EN 13285). The blend of sizes interlocks and compacts to a dense, load-bearing layer, which is why it is the default sub-base under driveways, patios and paths. It is made from crushed limestone, granite, or recycled crushed concrete conforming to BS EN 13242. (The 'MOT' name comes from the old Ministry of Transport.)
What is the difference between Type 1, Type 2 and Type 3 sub-base?: Type 1 (Clause 803) contains fines that fill the voids, giving maximum strength but little drainage. Type 2 is similar but allows more fines and a smaller top size — cheaper and fine for lightly loaded paths, but weaker. Type 3 (Clause 805) is a reduced-fines, open-graded 'permeable' sub-base — the dust is removed so water drains through it, making it the choice for SuDS-compliant permeable paving.
How deep should the sub-base be for a patio or driveway?: For a foot-traffic patio or path, 100 mm of compacted sub-base is normal. For a domestic driveway carrying cars, lay 150 mm. Soft, wet or clay ground may need 200 mm or more plus a geotextile membrane. Always compact in lifts of 75–100 mm or less — a deep layer laid in one go will never reach full density.
How do I calculate sub-base tonnage?: Work out finished volume as area (m²) × compacted depth (m). MOT Type 1 is delivered loose and compacts by about 30%, so order roughly 1.3× that volume and convert to tonnes at a loose density of about 1.85 t/m³. As a check, one tonne covers about 5 m² at 100 mm or 3.5 m² at 150 mm compacted. The calculator on this page does this automatically once you enter your area and depth.
Does sub-base need a geotextile membrane?: A woven geotextile membrane between the subgrade and the sub-base stops the stone punching into soft ground and prevents weeds and silt migrating up into the layer. It is strongly recommended on clay or wet ground and is cheap insurance on any driveway. On very soft ground a geogrid can be added to bridge weak spots.
Do I need planning permission for a new driveway?: In England, since 2008, a front driveway over 5 m² that uses an impermeable surface draining to the road needs planning permission. A permeable surface (such as permeable block paving on a Type 3 sub-base), or one that drains to a lawn or border, is permitted development. Wales has equivalent rules. Always check current SuDS guidance for your area.
How much should I compact MOT Type 1?: Lay it slightly damp and compact each 75–100 mm lift with a vibrating plate (wacker plate) for paths and patios, or a vibrating roller for driveways. Make several passes until the surface stops moving and rings solid. Light watering helps the fines bind. Proper compaction is what stops future sinking and rutting.

Open the MOT Type 1 calculator