Repair Systems — Roofing Defects
Pipe overflow systems for flat and low-pitched roof drainage
Pipe overflow systems use vertical or angled pipes installed at a set height above the primary outlet to provide secondary drainage on flat roofs. PVC and copper pipe systems are used in both new and remedial work, with the pipe top set at the emergency overflow activation level per AS/NZS 3500.3.
What are pipe overflow systems?
Pipe overflow systems are secondary drainage outlets that use a vertical or angled pipe installed through the parapet wall of a flat or low-pitched roof. The pipe inlet is set at 25–50mm above the primary drain invert level, ensuring the system activates only when primary drainage is blocked and water level rises to the emergency overflow height as required by AS/NZS 3500.3.
Product Reference
2 products — uPVC and copper pipe overflow systems — scroll to view all
Marley uPVC Roof Overflow Pipe DN100
uPVC gravity pipe overflow system — DN100
System Description
The Marley uPVC Roof Overflow Pipe DN100 is a gravity-operated pipe overflow system manufactured from unplasticised PVC, designed for use as a secondary overflow outlet on flat roofs and low-pitched roof areas in both new construction and remedial work. The system includes a top cap or strainer to prevent debris ingress while maintaining the required overflow hydraulic capacity, and a bottom outlet fitting for connection to the roof drainage system or controlled discharge point. The pipe is set with its inlet at 25–50mm above the primary drain invert level, ensuring the system activates only during an emergency overflow event as required by AS/NZS 3500.3. Available in standard 3m lengths, compatible with Colorbond metal roofing and concrete roof substrates. The uPVC material is cost-effective, widely available through plumbing trade supply, and suitable for the majority of standard flat roof overflow applications in Australian conditions. Confirm the current product range, sizing, and fixing details with Marley or your local plumbing supplier before specifying.
Technical Properties
- uPVC pipe body — DN100 — suitable for flat roof and low-pitched roof overflow applications
- Includes top cap or strainer — debris control while maintaining overflow hydraulic capacity
- Bottom outlet fitting included — connection to drainage system or controlled discharge
Limitations
- Must be set at correct activation height — 25–50mm above primary drain invert — incorrect height renders overflow system non-compliant
- uPVC — confirm suitability for extreme heat exposure on dark-coloured metal roofs — high surface temperatures may affect material performance
- Not a heritage-appropriate product — for heritage and premium applications, specify copper overflow pipe instead
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
Crane Copper Overflow Pipe System
Copper gravity pipe overflow system — DN75/DN100 — heritage applications
System Description
The Crane Copper Overflow Pipe System is a gravity pipe overflow system using soft-drawn copper tube in DN75 or DN100 diameters, assembled on site with soldered copper fittings. Copper is the preferred material for overflow pipe systems on heritage buildings and premium architectural projects where visual compatibility with existing copper or lead flashings, gutters, and downpipes is required. The through-parapet wall penetration is sealed with formed lead flashing bonded to the copper pipe body — the lead is dressed around the pipe and into the waterproofing membrane or roof substrate to provide a continuous, watertight seal. Copper overflow pipes develop a natural patina over time that is compatible with the aesthetic character of heritage buildings. Suitable for both new installation and remedial replacement of failed or undersized overflow outlets on heritage roofs. Confirm the current product range, tube grades, and soldering requirements with Crane Copper Tube before specifying.
Technical Properties
- Soft-drawn copper tube — DN75 and DN100 — assembled on site with soldered copper fittings
- Heritage and premium applications — compatible with existing copper flashings, gutters, and downpipes
- Formed lead flashing at through-parapet penetration — dressed around copper pipe and into waterproofing membrane
Limitations
- Higher cost than uPVC systems — material and labour costs for copper pipe and soldered fittings exceed uPVC alternatives
- Requires skilled plumber for soldered copper fitting assembly — not suitable for DIY installation
- Lead flashing at penetration — confirm current requirements and lead handling regulations with the project plumber and WHS adviser
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Comparison
Side-by-side comparison of pipe overflow systems. Confirm all product selections against the current manufacturer TDS before specifying.
| Product | Brand | Material | Pipe size | Installation | Suitable for |
|---|---|---|---|---|---|
| uPVC Roof Overflow Pipe DN100 | Marley | uPVC | DN100 | Cut to height on site — slip joint or solvent-weld fittings | Standard flat roofs — Colorbond and concrete — cost-effective |
| Copper Overflow Pipe System | Crane | Soft-drawn copper — soldered fittings | DN75 / DN100 | Soldered copper fittings — formed lead flashing at penetration | Heritage buildings — premium architectural — copper flashing compatibility |
Do not confuse pipe overflow systems with:
- Scupper overflow outlets — wall-mounted open-face overflow bodies are a different overflow mechanism to a through-wall pipe — scuppers are listed separately on the scupper systems page
- Weir overflow outlets — proprietary adjustable weir devices differ from a simple pipe overflow in mechanism and installation — weir systems are listed on the weir overflow systems page
- Primary drainage pipes — downpipes and primary drainage outlets are not overflow systems and must not be confused with a pipe overflow set at the emergency activation level
- Downpipe extensions — a pipe overflow is set at a height above primary drainage and is not the same as a downpipe extension or diverter
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.