To install treated wood on soil, begin by selecting durable, preservative-treated lumber rated for ground contact (e.g., UC-1 or higher). Dig post holes 12–18 inches deep, below the local frost line, and reinforce with concrete footings or pressure-treated pine blocks. Place posts 4–6 feet apart, ensuring level spacing. Secure horizontal members with galvanized screws or bolts. Backfill soil gently around posts to prevent shifting.

The installation method ensures longevity by addressing soil moisture and stability. Treated wood treated with chromated copper arsenate (CCA) or alternative preservatives retains effectiveness for 20–30 years when installed below ground level, per the American Wood Protection Association (AWPA). Properly placed footings prevent rot by keeping the wood 2–4 inches above soil, reducing moisture exposure. Studies show 85% of rot-related failures occur in wood above the frost line or in contact with damp soil. Code-compliant spacing (4–6 feet) distributes load evenly, minimizing soil compression. For example, a 2021 study in Landscape and Urban Planning found properly installed treated wood decks require 30% less maintenance than improperly spaced ones. Local building codes often mandate footings for posts over 4 feet tall, ensuring structural integrity. Using preservative-treated wood meeting AWPA standards reduces decay risk by 90% compared to untreated lumber in ground contact.