Educational Summary: Code Change Proposal RB165-22 (2024 IRC) APPROVED

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Educational Summary: Code Change Proposal RB165-22 (2024 IRC)​

The RB165-22 proposal brings important updates to drainage requirements and foundation construction in the IRC, with a focus on soil classification for residential foundations. Affected sections include R310.4.3 for area well drainage, R401.4.1 for soil evaluations, and numerous tables related to foundation requirements.

Key Changes​

1. Removal of R405.1 References:
   References to R405.1, which previously addressed foundation drainage requirements, are struck through in this proposal. This means that requirements for specific foundation drainage around concrete or masonry foundations have been removed from these sections. Consequently, foundation drainage decisions may now depend more on local amendments or builder discretion, with fewer prescriptive IRC requirements.
2. Relocation and Update of Soil Classification Table:
   The proposal relocates the soil classification table previously under R405.1 to R401.4.1. This change streamlines code navigation, placing the classification table closer to the relevant foundation sections. Additionally, a new column for USDA soil classifications has been added, supplementing the Unified Soil Classification System (USCS). The USDA classifications provide an accessible reference, especially useful when a full geotechnical evaluation is not available or feasible.
3. Guidance on Drainage and Suitability of Backfill Soils:
   With R405.1’s removal, drainage requirements in the remaining code focus on surface grading and adequate soil classification for backfill. A footnote added to the relocated soil table identifies certain soils as unsuitable for backfill due to poor drainage characteristics, highlighting the importance of using proper soil types for structural integrity.
4. Enhanced USDA and USCS Mapping:
   This proposal references a USACE study that aligns USDA soil textures with USCS categories, allowing builders to assess soil suitability more accurately without a geotechnical report. The mapping helps builders estimate load-bearing and drainage characteristics based on USDA classifications, reducing the need for site-specific testing while maintaining safety.

Key Affected IRC Sections​

• R310.4.3: Adjusts area well drainage requirements, with an exception allowing well-drained soils without a connected drainage system.
• R401.4.1: Hosts the updated soil classification table, incorporating USDA classifications for enhanced guidance on foundation construction.
• R403.3.3: Modifies drainage requirements for horizontal insulation around foundations, based on the updated soil classifications.
• Various R404 Tables: Updates foundation wall requirements, with specific reinforcement requirements now aligned to soil classifications in R401.4.1.

Cost Implications​

The removal of R405.1’s prescriptive foundation drainage requirements could potentially reduce upfront costs but may require builders to ensure adequate drainage through best practices or local guidance. Additionally, the USDA soil classifications allow builders to identify soil conditions that may warrant additional reinforcement or foundation adjustments, balancing cost with safety.

Public Hearing and Final Decision​

The ICC Committee approved RB165-22 as submitted, acknowledging that the updated soil classification information and USDA alignment provide valuable tools for builders. Some committee members expressed concerns about limited studies supporting the USDA alignment, but the proposal was accepted as a beneficial enhancement to the IRC.

In summary, RB165-22 clarifies and consolidates soil classification requirements, offering flexibility in foundation drainage and construction while relying on new soil classifications to guide safe building practices.