Low-slope roof systems must be designed with positive drainage to avoid ponding water, structural loading, and membrane deterioration. This article details the integration of roof drains and overflow scuppers with membranes, insulation, and vapor barriers.
Primary and Secondary Drainage Systems
- Primary drains typically consist of internal leaders connected to plumbing systems
- Scuppers provide overflow protection when primary drains are clogged or undersized
- Code requires overflow scuppers to be placed 2 inches above the primary drain elevation
- Drains and scuppers must accommodate expected flow rates based on rainfall intensity and roof area
Flashing and Membrane Integration
Drains should be fully clamped into place with compression rings or membrane clamps. Extend the roof membrane into the drain bowl and secure using manufacturer-approved sealants. Scuppers must be installed in boxed openings with welded flanges extending at least 4 inches into the wall assembly, wrapped and tied into WRB and insulation layers.
Code and Warranty Considerations
Drains must comply with ANSI/SPRI RD-1 standards. Overflow systems are mandated under IBC Section 1503. Scuppers should discharge onto a visible surface to avoid concealed water damage. Ensure that all components (clamps, gaskets, insulation rings) are compatible with the membrane type (TPO, EPDM, PVC, etc.).
Installation and QA Best Practices
- Pre-form insulation crickets around drains to promote positive drainage
- Ensure membrane fully covers and wraps into drain flange before clamping
- Inspect scupper joints and flange seals from both interior and exterior sides
- Water test all drain and scupper assemblies prior to cover board or ballast installation
Photograph drain installations at each stage to ensure compliance with manufacturer warranty and local inspection requirements.
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