Flat roof systems require more than membrane waterproofing—they need engineered drainage to prevent ponding and overflow. This article outlines roof drain layout, slope, and overflow considerations.
Overview
Roof drainage design starts with minimum slopes of 1/4″ per foot, per code. Strategically placed primary drains and overflow relief measures prevent ponding and roof collapse. Drainage must be integrated with structural layout and membrane detailing.
Drain Types and Layout
- Primary drains: Located at low points, connected to internal piping
- Overflow drains: Positioned above primary to serve as backup
- Scuppers: Wall exits sized per code for emergency flow
🔍 Quick Picks
- Cast Iron Roof Drain: Josam Roof Drain with Dome
- Overflow Scupper Kit: Wide Mouth Roof Scupper Drain
- Sealant Ring for Drains: Oatey Drain Flashing Seal
Code and Installation Notes
Follow IPC and local plumbing codes for pipe sizing and overflow elevation. Test roof slopes with laser levels before membrane installation. Avoid clogs by including dome strainers and access covers.
Conclusion
Roof drainage is essential to envelope integrity. Plan drain and overflow locations early in design to avoid expensive retrofits or damage caused by ponding and ice dams.
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