Clean No. 67 Stone Beneath Decks: When It Helps and Why It Won't Fix Poor Grading

Why Stone Alone Cannot Fix Standing Water

Gravel is a porous aggregate; water passes straight through it to the subsoil beneath. In the Piedmont region of North Carolina, native Cecil clay subsoils have slow percolation rates.

When rainwater drips through deck board gaps onto flat dirt covered with stone, it cannot soak downward quickly. Instead, it follows gravity along the surface. If that surface lacks at least 6 inches of fall in the first 10 feet away from the foundation (the standard slope required by NCRC Section R401.3), water migrates toward the foundation stem wall. Adding gravel without correcting the grade merely hides the standing water from view.

The Correct Five-Step Installation Sequence

To install gravel beneath a deck so it performs properly for decades without creating moisture hazards, AGCS follows a strict construction sequence:

• Rough Grading: Shape the bare earth beneath the proposed deck footprint so it pitches away from the foundation at a minimum 2% slope (roughly 1/4 inch of fall per foot, or 6 inches over 10 feet).
• Surface Smoothness & Compaction: Rake out clods, roots, and depressions that could hold puddles. Tamp or roll the clay subgrade.
• Woven Geotextile Fabric: Lay a heavy-duty commercial woven geotextile weed barrier (minimum 4 to 6 oz weight). Overlap all seams by at least 12 inches and pin them with 6-inch steel landscape staples. Cheap perforated black plastic shreds and traps stagnant water.
• Clean Stone Layer: Spread 2 to 3 inches of clean, washed NCDOT No. 67 granite stone (stones roughly 1/2 to 3/4 inch in size, completely free of stone dust and fines). Never use crusher run (ABC stone) beneath a deck, because stone dust packs tight and creates an impermeable muddy crust.
• Perimeter Containment: Trench a treated border or steel edging at the outer drip line to keep gravel from washing out into the lawn.

Code Standards and Primary Technical References

Our deck construction practices comply with verified residential building standards:

2018/2024 North Carolina Residential Code (NCRC), Section R401.3 (Drainage Surface Grade)

2018/2024 NCRC Appendix M (Prescriptive Deck Construction Guidelines)

NCDOT Standard Specifications for Roads and Structures, Section 1005 (Coarse Aggregate Gradation Table for No. 67 Stone)

American Wood Protection Association (AWPA) Standard UC3B / UC4A (Wood Preservation Field Retention)