Repair Systems — Roofing Defects
Weir overflow outlet systems for box gutter and flat roof compliance
Weir overflow outlets provide a controlled spill edge that activates at a precise water level above the primary drain to protect against roof flooding. Proprietary weir systems from Alproc and Blucher are designed with adjustable weir height and stainless steel or aluminium bodies to integrate with waterproofing membranes.
What are weir overflow systems?
Weir overflow outlets are proprietary secondary drainage devices that provide a controlled spill edge at a precise water level above the primary drain. Unlike scupper outlets that discharge through an open face in the parapet wall, a weir outlet spills water over an adjustable weir blade when the water level rises to the overflow activation height — typically 25–50mm above the primary drain invert as required by AS/NZS 3500.3.
Product Reference
2 products — aluminium and stainless steel weir overflow outlets — scroll to view all
Alproc Weir Overflow Outlet
Aluminium weir overflow outlet — adjustable — powder-coated Colorbond
System Description
The Alproc Weir Overflow Outlet is an aluminium alloy weir body fitted with an adjustable weir blade that can be raised or lowered ±30mm from the nominal setting, allowing precise on-site calibration of the overflow activation level above the primary drain. The weir body is available in widths from 150mm to 300mm, providing flexibility in hydraulic capacity to suit varying roof areas and design rainfall intensities as calculated under AS/NZS 3500.3. The integral membrane flange provides a positive connection point for waterproofing membrane installation — liquid-applied and sheet membranes can be bonded directly to the flange. The powder-coat finish is available in the Colorbond range, allowing the outlet to be colour-matched to box gutter linings, roof flashings, and cladding. Suitable for box gutters, parapet-bounded flat roofs, and internal gutter overflow applications. Confirm current product specifications, weir blade adjustment range, and membrane compatibility with Alproc Australia before specifying.
Technical Properties
- Aluminium alloy body — adjustable weir blade ±30mm — precise on-site overflow level calibration
- Width range 150–300mm — hydraulic capacity to suit varying roof areas per AS/NZS 3500.3
- Integral membrane flange — positive connection for liquid-applied and sheet waterproofing membranes
Limitations
- Aluminium — confirm suitability for coastal and marine environments — may require anodising or marine-grade coating in severe coastal zones
- Adjustable weir blade must be locked at the correct position after calibration — confirm locking mechanism with Alproc before installation
- Width selection must be confirmed against hydraulic capacity calculation — wider weir does not automatically guarantee AS/NZS 3500.3 compliance
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
Blucher Weir Drain W400
Stainless steel weir overflow outlet — DN100 — coastal grade AISI 316
System Description
The Blucher Weir Drain W400 is a stainless steel weir overflow outlet manufactured from AISI 316 stainless steel, designed for use in flat roof and box gutter overflow applications where corrosion resistance is a primary selection criterion. AISI 316 provides significantly better resistance to chloride corrosion compared to 304-grade stainless steel, making the W400 the appropriate specification for buildings in coastal and marine environments where salt-laden air accelerates corrosion of standard drainage fittings. The DN100 outlet connects to the discharge drainage system, and the integrated clamping ring provides a positive mechanical seal for sheet waterproofing membranes — the membrane is clamped between the weir body and the clamping ring to form a watertight seal without relying solely on adhesive. The W400 is suitable for high-specification commercial roofing and flat roof applications in coastal locations, premium developments, and where a stainless steel overflow outlet is preferred over aluminium for longevity and corrosion resistance. Confirm current product specifications, weir height setting, and membrane clamping ring compatibility with Blucher Australia before specifying.
Technical Properties
- AISI 316 stainless steel body — superior chloride corrosion resistance for coastal and marine environments
- DN100 outlet — connects to discharge drainage system — confirm discharge routing and capacity
- Integrated clamping ring — positive mechanical seal for sheet waterproofing membranes
Limitations
- Higher cost than aluminium weir alternatives — AISI 316 stainless steel carries a material cost premium over powder-coated aluminium
- Weir height may be fixed or have limited adjustment — confirm adjustment range with Blucher before specifying where fine calibration is required
- Integrated clamping ring is designed for sheet membranes — confirm compatibility with liquid-applied membrane systems with Blucher technical
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Comparison
Side-by-side comparison of weir overflow outlet systems. Confirm all product selections against the current manufacturer TDS before specifying.
| Product | Brand | Material | Weir width | Adjustment | Membrane connection |
|---|---|---|---|---|---|
| Weir Overflow Outlet | Alproc | Aluminium alloy — powder-coated Colorbond | 150–300mm — selection by hydraulic requirement | Adjustable weir blade ±30mm | Integral membrane flange — liquid and sheet membranes |
| Weir Drain W400 | Blucher | AISI 316 stainless steel | DN100 outlet — confirm weir face width with Blucher | Confirm adjustment range with Blucher | Integrated clamping ring — sheet membranes |
Do not confuse weir overflow systems with:
- Scupper overflow outlets — wall-mounted open-face scuppers are a different overflow mechanism to a weir outlet — scupper systems are listed on the scupper systems page
- Pipe overflow systems — through-wall pipe overflows set at the emergency level differ from a weir body in design, installation, and hydraulic behaviour — pipe systems are listed on the pipe overflow page
- Primary drain outlets — box gutter primary drainage outlets and puddle flanges are not overflow devices and must not be set at the same level as the weir overflow
- Free overflow edges — an uncontrolled spill edge at the end of a box gutter or roof is not the same as a compliant proprietary weir overflow outlet designed to the required activation level
Disclaimer
This page provides general technical information only. Final product selection must be confirmed against the current manufacturer technical data sheet, project specification, substrate condition, exposure level, drainage design, NCC requirements, AS/NZS 3500.3 requirements, and applicator warranty conditions. Do not rely on this reference as a substitute for professional engineering or hydraulic consultant advice.