CSLB C-27 Landscaping ContractorHardscape and FeaturesEasy
A homeowner wants to install a permeable paver patio in their backyard. Which sub-base material is most appropriate for ensuring proper drainage and structural integrity for this type of installation?
- ACrushed gravel with fines (e.g., decomposed granite)
- BSand over geotextile fabric
- CWashed angular aggregate (e.g., 3/4-inch clean stone)
- DCompacted clay
Show answer & explanationAnswer & explanation
Correct answer: C. Washed angular aggregate (e.g., 3/4-inch clean stone)
For permeable paver systems, a washed angular aggregate sub-base provides the necessary void space for water infiltration and sufficient structural support. Clay and decomposed granite would impede drainage, while sand alone lacks the required load-bearing capacity for a patio sub-base.
Why the other options are wrong
- A. Crushed gravel with fines (like decomposed granite) has too many small particles that would clog the voids and reduce permeability.
- B. While sand is used as a bedding layer, it is not suitable as a primary sub-base for structural support, especially for permeable systems.
- D. Compacted clay is impermeable and would prevent drainage, defeating the purpose of permeable pavers.
Permeable Paver Sub-base
The foundational layer beneath permeable pavers, designed to allow water to infiltrate and provide structural support.
- Must be highly permeable to allow drainage.
- Composed of angular, washed aggregate.
- Provides structural stability for the paver system.
Memory trick: Permeable patios need a CLEAN base to let water flow. No dirt, just drain!