Type 3 sub-base
Plain English. Practical detail. UK context.
Type 3 sub-base describes a specified open-graded aggregate used in suitable construction, including some permeable paving arrangements. It differs from simply ordering any rubble or ordinary Type 1 material. Grading, source, condition and the complete pavement design determine suitability; the name alone does not establish load capacity or drainage performance.
Last reviewed: (editorial review against the public sources listed below).
Open voids have a purpose
GOV.UK's front-garden guidance explains that open-graded sub-base materials can allow water movement and temporary storage beneath suitable surfaces. Fine material can fill voids and change that behaviour. Homeowners should ask which material and specification are proposed rather than accept a generic hardcore description. Trainees should identify the design requirement and product information, not judge solely by how angular the stone looks. A material suitable for one permeable system is not automatically approved for every driveway, foundation or drainage trench.
The complete pavement still needs design
Ground strength, intended loads, surface, separation layers, levels and water destination affect the construction. An open-graded layer over unsuitable conditions does not make every site drain. The older government guidance explains principles but is not a substitute for current project-specific design or planning checks. This reference gives no universal depth or compaction schedule. A trainee should report soft ground, contamination or a retained layer differing from the specification. Simply adding more aggregate can conceal rather than resolve an underlying problem and may change levels at the house or boundary.
Keep the intended drainage route working
A porous finish, appropriate base and suitable discharge or infiltration arrangement need coordination. Runoff should not be sent casually towards a building, neighbour or unauthorised drain. Construction contamination and later soil or sand can affect performance. Homeowners should understand normal maintenance for the actual surface. Trainees should protect the specified aggregate from mixing with unsuitable materials and coordinate edges and outlets before surfacing. A successful-looking surface test does not necessarily verify every underlying storage, soil or overflow assumption. Record relevant checks and limitations rather than promise universal flood prevention.
Safety, scope and records
HSE underground-service guidance is relevant before excavation, including domestic driveways. Handling, machinery, dust and access need planned controls. Agree material, specification, excavation, preparation, drainage, disposal and concealed-stage checks. Prices and outcomes vary from job to job, so compare written, itemised quotations rather than relying on a typical figure. Tradespeople should retain delivery and project information and obtain approval for substitutions. Homeowners should keep the pavement specification for later alterations, since replacing or contaminating a critical layer can undermine the intended system even where the visible finish remains attractive.
Frequently asked questions
Is any clean rubble equivalent to Type 3?
No. Check the actual grading, specification, quality and intended use.
Does Type 3 guarantee a permeable driveway?
No. The surface, ground, drainage and complete build-up must support the intended performance.
Sources and further reading
Public sources and further reading. Sources checked: 8 November 2026. Consult the original for details and later changes.