Type 1 Granite Sub Base

What is Type 1 Granite Sub Base?

MOT Type 1 Sub Base – Description and Usage Guide

Introduction

MOT Type 1, also referred to as Type 1 Sub Base, is a granular aggregate material approved by the Ministry of Transport (MOT) in the UK for use as a sub-base in highway and construction works. It is one of the most widely used materials in groundwork and construction due to its load-bearing strength, compaction properties, and versatility.

In this comprehensive guide, we will cover the composition, characteristics, standards, uses, application methods, and advantages of MOT Type 1 Sub Base, as well as best practices for installation.

What is MOT Type 1 Sub Base?

Definition
MOT Type 1 Sub Base is a well-graded granular material that provides a stable, load-bearing base layer beneath surfaces such as roads, pavements, patios, driveways, and foundations. It is named after the specifications laid out by the UK’s Department for Transport in the Specification for Highway Works (SHW), Clause 803.

Composition
MOT Type 1 is typically composed of:

Crushed rock (such as granite, limestone, or basalt)
Concrete or recycled aggregate (in eco-friendly variants)

Particles ranging from 40mm down to dust
The key characteristic is the well-graded nature of the material: larger stones interlock for strength, while the finer particles fill voids and allow for optimal compaction.

Size Specification
The particle size distribution includes:

Maximum aggregate size: 40mm
Fines content: typically below 5mm, including dust
Well-graded to ensure minimal voids after compaction


Properties of MOT Type 1

Mechanical Strength
MOT Type 1 is renowned for its high load-bearing strength, making it suitable for heavy-duty applications such as highways and commercial driveways.

Compaction and Stability
Due to the inclusion of fines, the material compacts well with minimal movement over time. This provides a firm, stable platform for surface layers.

Drainage Characteristics
While not as permeable as Type 3 or open-graded materials, it offers moderate drainage performance. In high-water areas, additional drainage systems are often recommended.

Frost Resistance
The fines in MOT Type 1 can retain moisture and, under freezing conditions, may contribute to frost heave. Appropriate design considerations should be taken in frost-susceptible areas.

Type 1 Granite Sub Base 0-40mm Uses and Applications

• Sub-base for driveways and parking areas (light to heavy-duty)
• Base layer for paved patios, paths, and walkways
• Bedding layer for block paving or setts
• Compacted base for tarmac surfaces
• Temporary access tracks on construction or landscaping sites
• Fill material for trenches, service ducts, or low spots
• Base for garden sheds, decking, and small outbuildings
• Drainage layer beneath patios, paths, or slabs
• Core material for retaining walls or garden steps
• Reinforced concrete aggregate for footings or small foundations
• Levelling low-lying areas in gardens or construction sites
• Soil stabilisation in mixed fill projects
• Base for light gravel driveways or decorative gravel areas
• Levelling material under garden ornaments, planters, or statues
• Sub-base under kerbs, edging stones, or raised patios