Building a 12 by 16 paver patio off the back door in sandy soil.

Base Layers (bottom to top):

1. Subgrade: Compact native sand to 98% SPD (Standard Proctor Density). No fabric needed on sand unless silt/clay is present.
2. Base: 4" compacted 3/4" minus crushed stone (road base/Class 5). Compact in 2" lifts. Final surface must not deviate > 3/8" over 10 ft.
3. Bedding Layer: 1" concrete sand (ASTM C33 / washed bedding sand). Screed flat—do not compact before laying pavers.
4. Pavers: Place, run plate compactor with urethane pad, sweep polymeric sand into joints, compact again, blow clean.

Slope: 2% (1/4" per foot) minimum away from structure.

• 16-ft run = 4" total drop from house to yard edge.
• 12-ft width = 3" drop side-to-side (crown or single plane).

Code/Standard: ICPI Tech Spec 2 / IRC R403.1 (drainage away from foundation).

Critical Details:

• Edge Restraint: Required on all open sides (snap-edge + 10" spikes @ 16" OC).
• Excavation Depth: ~7" below finished paver surface (4" base + 1" sand + 2 3/8" paver).
• Compaction: Plate compactor (5,000+ lbf) for base; hand tamper for corners.
• Door Threshold: Finished paver surface min. 4" below door sill (IRC R311.3.1) to prevent water entry.

Sandy Soil Advantage: Excellent drainage. Skip geotextile unless separating base from silt/clay subsoil.

For a 12' x 16' paver patio on sandy soil, proper base preparation and slope are critical for drainage and longevity. Here’s what to do:

Base Layers (from bottom up):

1. Subgrade: Compact native sandy soil. Sandy soil drains well but can shift; ensure it’s firm and level after compaction.
2. Geotextile Fabric (Recommended): Lay permeable landscape fabric over subgrade to prevent sand migration and weed growth (ICPI Tech Spec 2).
3. Base Aggregate: 4–6 inches of crushed stone (¾" minus, like Class 2 base or road base). Compact in 2" lifts with a plate compactor. Sandy soil allows good drainage, so 4" may suffice if compacted well, but 6" is safer for long-term stability.
4. Bedding Sand: 1 inch of coarse, washed concrete sand (not mason sand). Screed to a smooth, level surface. This allows pavers to settle slightly and lock in place.

Slope: Pitch the patio 1/4 inch per foot away from the house for drainage. For a 16' depth (assuming the 16' side runs from house outward), that’s 4 inches of total drop (16 × 0.25 = 4").

• Start at the house door threshold (high point).
• Slope uniformly across the entire patio toward the far edge or to a drainage swale if water pools.
• Use a 4-ft level with a 1/4" shim under one end to check slope during screeding.

Important Notes:

• Edge restraints (plastic or metal) are required to prevent lateral spread.
• Polymeric sand in joints after installation helps lock pavers and resist weeds.
• If the patio is adjacent to a foundation, ensure slope directs water at least 5' away from the house (IRC R401.3).
• For sandy soil, no additional drainage pipe is usually needed unless water tables are high.

This follows ICPI and IRC best practices. If unsure about soil stability or local codes, consult a licensed hardscape contractor. (Word count: 248)