Trusted by Aussie Roofers
Engineered upstream direction-change devices designed to safely redirect water flow and navigate complex box gutter layouts without compromising hydraulic capacity.
Maintain full hydraulic capacity with our patented step-down mechanism that controls water direction while preventing backwatering into the upstream section.
The only independently certified upstream direction-change devices in Australia, engineered to meet AS/NZS 3500.3:2021 and NCC standards.
Two-part sliding design requires clearance as low as 50mm to 70mm below the sole of the box gutter, eliminating the need for internal pipework and bulkheads.
Manufactured from high-grade, corrosion-resistant steel designed to withstand harsh Australian weather conditions and maintain long-term structural integrity.
Dam Buster Elbows (ELB) and Junctions (TJN, CJN) are precision-engineered upstream direction-change devices designed to safely redirect water flow in box gutter drainage systems. Installed upstream of the discharge point, these components allow box gutters to navigate corners, structural obstructions, and multi-gutter joins without restricting hydraulic capacity or compromising compliance.
In traditional box gutter designs, redirecting water flow heavily restricts where water can discharge, often forcing gutters to run straight to an external wall and relying on bulky internal bulkheads and PVC pipework. This approach is labour-intensive, costly, and frequently results in compliance issues during plumbing audits. Dam Buster Elbows and Junctions eliminate this limitation entirely.
The core technology behind these devices is the step-down mechanism. Operating effectively as an open-sided sump, the elbow or junction redirects water 90 degrees by dropping the floor level of the gutter at the change-of-direction point. This immediate drop prevents backwatering into the upstream section while simultaneously giving the downstream box gutter additional freeboard, ensuring it can easily carry the combined flow rate of the entire system.
Dam Buster Elbows and Junctions are used across residential, commercial, and industrial roofing projects throughout Sydney and beyond. They are particularly valuable on buildings with complex architectural rooflines, parapet walls, or tight ceiling cavities where internal pipework is physically impossible or cost-prohibitive. With clearance requirements as low as 50mm to 70mm, these devices provide massive flexibility in shallow fascia or tight ceiling spaces.
The devices are supplied as two sliding components, allowing easy on-site adjustment to fit the exact width of your box gutter. Available in 90-degree Left-Hand or Right-Hand elbows, T-Junctions for inline joins, and Corner Junctions for building edges, these products are fabricated with a precise built-in 1-in-200 fall to guarantee gravity-assisted drainage without manual site shimming.
HMR Supplies manufactures the Dam Buster Elbows and Junctions range locally at our Revesby, Sydney facility. This allows us to provide rapid turnaround times, custom fabrication for non-standard gutter profiles, and direct technical support for roofing contractors, plumbers, and builders across the Sydney metro area.
Whether you are working on a new architectural build with a complex parapet wall layout, managing a large-scale commercial roof, or retrofitting an existing system to meet current NCC requirements, Dam Buster Elbows and Junctions provide the only independently certified upstream direction-change solution available in Australia.
Product Type:
Upstream Direction-Change Device
Material
High-grade corrosion-resistant steel
Application
Box gutter drainage systems
Configurations
Elbow (ELB), T-Junction (TJN), Corner Junction (CJN)
Angles Available
90° Left-Hand (LH) and Right-Hand (RH)
Gutter Width Range
200mm–600mm (custom sizes available)
Clearance Required
50mm–70mm below the sole of the box gutter
Built-in Fall
1-in-200 for gravity-assisted drainage
Compliance
AS/NZS 3500.3:2021 and NCC certified
Suitable For
Residential, Commercial, Industrial, Architectural
Water travels along the box gutter toward a corner, obstruction, or junction point
The elbow or junction receives the water and redirects it 90 degrees to the required flow path
The built-in floor drop prevents backwatering upstream while increasing freeboard in the downstream channel
Water continues along the downstream box gutter toward the certified outlet device
Water travels along the box gutter toward a corner, obstruction, or junction point
The elbow or junction receives the water and redirects it 90 degrees to the required flow path
The built-in floor drop prevents backwatering upstream while increasing freeboard in the downstream channel
Water continues along the downstream box gutter toward the certified outlet device
Install the elbow or junction at the upstream direction-change point, never at the discharge outlet.
Stand facing downstream to confirm Left-Hand or Right-Hand orientation before fixing.
Slide the two-part components to match the exact width of your box gutter before securing.
Ensure the built-in 1-in-200 fall is correctly aligned with both upstream and downstream gutter channels.
Test water flow to confirm correct direction change, zero backwatering, and compliant performance.
Install the elbow or junction at the upstream direction-change point, never at the discharge outlet.
Stand facing downstream to confirm Left-Hand or Right-Hand orientation before fixing.
Slide the two-part components to match the exact width of your box gutter before securing.
Ensure the built-in 1-in-200 fall is correctly aligned with both upstream and downstream gutter channels.
Test water flow to confirm correct direction change, zero backwatering, and compliant performance.
Australian-designed rain heads engineered to safely discharge water from box gutters and perform reliably during extreme rainfall events.
Innovative direction-change devices designed to redirect water flow safely from box gutters to the point of discharge.
Short answer: Colorbond is Zincalume with paint on it. Everything else follows from that. They are not competing products from rival manufacturers. Colorbond is made by taking Zincalume steel and
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Use an Elbow (ELB) when a single box gutter needs to navigate around a corner or obstruction. Use a Junction (TJN or CJN) when two separate box gutters need to connect together and merge their water flow into a single downstream channel.
Stand facing downstream — the direction the water is moving. If the gutter needs to turn to your left, you require a Left-Hand (LH) elbow. If it needs to turn to your right, you require a Right-Hand (RH) elbow.
Yes. Our devices are fabricated with a two-part sliding design, allowing them to adjust and fit perfectly into any standard box gutter with a width between 200mm and 600mm.
No. Elbows and junctions are strictly upstream direction-change devices. They do not have overflow capabilities. If you need to change direction at the actual point of discharge, you must use a Side Outlet instead.
Absolutely. If your project features an unusually wide box gutter or specific architectural requirements outside standard dimensions, HMR Supplies can fabricate custom steel drainage fittings to match your exact specifications.
Our team can help you select the best drainage solution for your project.
For all quote requests or general enquiries, please complete the below form and our team will respond as soon as possible.
