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Sill Recess Requirements for Flush Transitions

Mariane Garcia
  • Updated

Framing details and field recommendations for zero-step entries

Creating a flush or “zero-step” transition between interior flooring and exterior thresholds requires careful planning at the framing stage. This article outlines the sill recess requirements and field best practices to ensure clean lines, code compliance, and long-term performance.

 

Why Sill Recess Matters

A flush transition between the interior floor and the sill:

  • Supports ADA and universal design requirements

  • Enhances modern architectural aesthetics

  • Eliminates tripping hazards and improves accessibility

  • Requires detailed coordination with slab or subfloor elevations, waterproofing, and drainage

 

Typical Sill Recess Dimensions

Recess depth and width depend on your selected Mosaic door system and sill type (e.g., multi-slide, swing, or pivot). As a general guideline:

  • Recess Depth: 1" to 2.5" below finished floor level

  • Recess Width: Equal to or slightly wider than the sill footprint (typically 4" to 6")

  • Drainage Allowance: Integrated slope or drain path must be planned for exterior exposure

Always reference your project-specific shop drawings for exact dimensions.

 

Framing & Subfloor Considerations

  1. Coordinate Early
    Ensure your architect, framer, and concrete team are aligned before the foundation or deck is poured. Once set, these details are difficult to change.

  2. Recess Into Slab or Framing

    • For slab-on-grade: Form a depression or “pan” into the concrete pour

    • For wood-framed floors: Drop the sill area using blocking, stepped joists, or subfloor cutout

  3. Support & Leveling
    The recess must be flat, level, and structurally reinforced to support the full sill width without deflection.

  4. Drainage Planning
    For exterior systems, especially flush sills, integrate a drain mat, trench drain, or slope away from the sill. Never rely solely on sealant for water protection.

 

Waterproofing Guidelines

  • Use liquid-applied or membrane waterproofing under and around the sill recess

  • Seal all corners and transitions to prevent water intrusion

  • Extend flashing 6" up vertical framing and fully under the sill

  • For exterior installations, use pan flashing compatible with your selected door material

 

When Flush Transitions Aren’t Recommended

Avoid flush transitions where:

  • Snow or heavy rain exposure is frequent without adequate drainage

  • Decks or slabs slope back toward the opening

  • There is no structural recess available to lower the sill safely

In these cases, a low-profile or stepped sill may be a better long-term solution.

 

Resources & Support

To confirm framing requirements for your specific door system, contact:

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