How Deep Should Sand Be Under Pavers?
Interpret the nominal loose screeded bedding layer, avoid using sand to fix base grades and recognize assemblies that require different setting materials.
For CMHA’s conventional sand-set interlocking concrete pavement method, bedding is screeded to a nominal 1 inch (25 mm) while loose. This describes an uncompacted setting bed, not an instruction to install one inch of precompacted sand below every kind of paving.
Read “uncompacted screeded” literally
The bedding is graded to a consistent layer before placing units; consolidation occurs as the assembly is installed and compacted. A loose layer depth and final consolidated depth are not interchangeable measurements. Do not repeatedly compact and top up sand to manufacture a final one-inch bed unless the selected system specifically requires that procedure.
Set screed rails and surface elevations from the project detail and anticipated installation behavior. Confirm the paving manufacturer’s compaction instructions, particularly for slabs or sensitive surfaces. The selected finished elevation matters at drains, doors and existing paving.
Grade the base before spreading sand
The aggregate base must establish the supporting profile. Bedding follows that profile at a substantially uniform thickness. If the base has a depression, adding deeper sand locally creates a different setting condition instead of correcting the base.
Geometry example: a nominal 1-inch bed over most of a patio but a 2-inch bed over a low area doubles bedding volume in that area. A calculator can quantify the extra volume; it cannot make the uneven assembly structurally suitable. Correct the base in accordance with the selected construction detail before screeding.
Excessive or varying bedding thickness can lead to uneven consolidation and movement under loading. CMHA’s construction and vehicular bedding guidance treats layer preparation and suitable sand as coordinated installation decisions, not a leveling shortcut.
Recognize a different system before reusing the number
Permeable paving uses an open-graded bedding detail. Proprietary panels, mortar-set paving, rigid overlays and some large-format products may require other setting layers. Read their complete assembly instructions; a paver-shaped unit is not evidence that a conventional sand bed applies.
Also distinguish the setting layer from any sand specified to prepare ground below a proprietary panel. Similar material names do not make those positions or thicknesses interchangeable.
Measure and estimate the selected layer
Record the intended screeded depth, paved area and any sections using another assembly. Exclude base-only extensions. Volume is area × depth after converting inches to feet; optional weight needs supplier density.
When comparing a revised design, update excavation depth as well as sand quantity. Changing the setting layer affects final elevations and compatibility, so do not change it solely to reduce material cost.
Enter the specified nominal screeded layer in the Paver Sand Calculator. The bedding quantity guide walks through volume, allowance and purchasing conversions without hiding density assumptions.
Sources and scope
- CMHACMHA PAV-TEC-002 (formerly Tech Spec 2 / Tech Note 2): Construction of Interlocking Concrete Pavements
Conventional interlocking concrete pavement construction; scoped base minimums and nominal uncompacted bedding guidance.
- CMHABedding Sand Selection for Interlocking Concrete Pavements in Vehicular Applications — PAV-TEC-017
Bedding gradation and durability considerations for vehicular applications.
- CMHAConstruction of Permeable Interlocking Concrete Pavement Systems — PAV-TEC-018
Open-graded bedding, base and reservoir construction in permeable systems; not a substitute conventional sand-set detail.
Material specifications, construction guidance and product instructions have different scopes. Example inputs demonstrate calculations; they are not project defaults.