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Engineered box gutter collection devices designed to rapidly discharge high volumes of stormwater and protect commercial and residential buildings from internal flooding.
Operates in genuine free flow conditions in accordance with Figure I1 of AS/NZS 3500.3 in both normal and overflow states, eliminating backflow issues and ensuring maximum water clearance.
Engineered to meet NCC and AS/NZS 3500.3:2021 requirements. Full compliance documentation provided to assist with NSW Performance Solutions.
The patented dual-chamber system manages normal flow through the primary chamber while safely discharging overflow to atmosphere via a secondary chamber, providing absolute protection against internal flooding.
Manufactured from 0.55 BMT Colorbond®, Zincalume®, Colorbond® Ultra, and Marine Grade 316 Stainless Steel for long-term performance in any environment.
The Dam Buster Free Flow Sump is a precision-engineered box gutter drainage device that operates as the critical collection transfer point between a horizontal box gutter and a vertical downpipe. By establishing a lowered reservoir section at the lowest point of the drainage system, it facilitates the rapid, unhindered transfer of stormwater from the roof into the broader drainage network during severe weather events.
Unlike traditional code-specified sumps, the Dam Buster Free Flow Sump entirely removes the requirement for water to back up and rise inside the box gutter before the overflow condition activates. Standard market sumps present a high risk of internal building flooding if the primary outlet is overwhelmed. By utilising a patented dual-chamber system, these advanced sumps deliver total water management efficiency, giving trade professionals absolute confidence in their installations.
The mechanics are straightforward and highly effective. Under normal weather conditions, the primary chamber collects stormwater and channels it efficiently down the main vertical outlet into the stormwater system. If a severe storm overwhelms the primary chamber or debris blocks the main downpipe, water crests an internal dividing weir and spills into the secondary overflow chamber. From here, it is safely discharged to atmosphere via a secondary overflow downpipe, satisfying all building code requirements.
These units are factory-made in standard 100mm increments to suit all standard box gutter widths from 200mm up to 600mm. Material options include standard Colorbond® and Zincalume® for residential and commercial applications, and Marine Grade 316 Stainless Steel for aggressive coastal or industrial environments. For projects with non-standard dimensions, HMR Supplies fabricates custom roof sumps tailored to your specific architectural plans, complete with precise nozzle positioning to match your exact internal plumbing layout.
Sizing is straightforward using the flow rate tables in the Dam Buster Product Technical Statement. Units are selected strictly by litres per second without requiring complex hydraulic formulas on site. This means the box gutter can be sized independently of the sump, simplifying your entire hydraulic framework and significantly reducing engineering sign-off time.
HMR Supplies manufactures the full Dam Buster Free Flow Sump range locally at our Revesby, Sydney facility. This ensures fast turnaround times, direct technical advice for builders, plumbers, and roofing contractors, and full custom fabrication capability to keep your site schedule on track.
Product Type:
Free Flow Box Gutter Sump
Material
Colorbond® 0.55 BMT, Zincalume®, Colorbond® Ultra, Marine Grade 316 Stainless Steel
Application
Internal box gutter drainage systems
Chamber Design
Patented dual-chamber (primary flow + overflow to atmosphere)
Gutter Width Range
200mm–600mm in 100mm increments (custom sizes available)
Compliance
AS/NZS 3500.3:2021 Figure I1, NCC certified
Flow Standard
Free flow conditions — normal and overflow states
Performance Solution
Technical documentation supplied for NSW certification
Installation Type
Internal box gutter, vertical downpipe connection
Suitable For
Residential, Commercial, Industrial, Architectural
Rainwater collects in the box gutter and flows along the gradient toward the rain head
The rain head receives and manages incoming water at the discharge point
Water flows safely into the connected downpipe system under normal conditions
If the downpipe blocks, excess water rises to the 25mm weir and spills externally, fully bypassing the building interior
Stormwater flows from the box gutter into the primary chamber of the sump
The primary chamber collects and manages incoming water under normal conditions
Water flows efficiently down the main vertical outlet into the stormwater system
If the primary outlet is overwhelmed, water crests the internal weir into the secondary chamber and discharges safely to atmosphere
Place the sump at the designated low point of the box gutter run, directly over the primary internal downpipe.
Mechanically fix and fully seal the unit to the box gutter using high-grade sealants to prevent leaks at the connection point.
Connect the primary chamber outlet to the main stormwater line.
Route the secondary overflow pipe so it discharges to a clearly visible external location as required by code.
Test water flow through both chambers to confirm correct primary discharge and compliant overflow performance before finalising the installation.
Place the sump at the designated low point of the box gutter run, directly over the primary internal downpipe.
Mechanically fix and fully seal the unit to the box gutter using high-grade sealants to prevent leaks at the connection point.
Connect the primary chamber outlet to the main stormwater line.
Route the secondary overflow pipe so it discharges to a clearly visible external location as required by code.
Test water flow through both chambers to confirm correct primary discharge and compliant overflow performance before finalising the installation.
Relying on rule-of-thumb measurements instead of calculating the exact litres-per-second flow rate for the catchment area is the most frequent compliance failure on site.
Installing a sump too far from the major water collection zone, or failing to provide adequate gutter fall, limits the system’s ability to clear water fast enough during peak storm events.
If the primary and overflow nozzles do not perfectly align with internal wall cavities or external pipework, inefficient pipe bends restrict flow and compromise compliance. Map out your downpipe locations thoroughly before sending your order to the factory.
Australian-designed rain heads engineered to safely discharge water from box gutters and perform reliably during extreme rainfall events.
Engineered components that allow upstream direction changes in box gutter systems while maintaining efficient drainage flow.
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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Yes. While we supply standard sizes in 100mm increments from 200mm to 600mm, HMR Supplies operates a full precision metal manufacturing facility in Sydney. If you require unique dimensions, specific outlet placements, or specialised materials, we will fabricate a unit to your exact project specifications.
Absolutely. You can retrofit these units directly into existing box gutter systems. Because the box gutter acts independently of the sump in a free-flow design, upgrading an old, non-compliant sump to a Dam Buster system is a highly effective way to fix chronic overflow or backflow issues on older commercial buildings.
Yes, generally speaking, a Performance Solution is required for certification in New South Wales. We provide all the necessary technical documentation, sizing tables, and testing data to assist your hydraulic engineer or certifier in quickly approving the installation.
Standard sizes in common materials like Colorbond® and Zincalume® are processed rapidly from our Revesby facility. Custom fabrications or specialised materials such as Marine Grade Stainless Steel may require a slightly longer production schedule. Contact our team with your exact specifications for a precise delivery timeframe.
Our team can help you select the best drainage solution for your project.
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