Looking for a fast and reliable way to size your box gutter overflows in Melbourne? Our Dam Buster Sizing Cheat-Sheet makes it simple for roofers, plumbers, and builders to get the right kit every time.
Using Melbourne’s official rainfall intensity of 170 mm/h, the quick-pick table helps you match roof area and gutter length to the correct Dam Buster kit in seconds. We’ve included real Melbourne job examples, a one-line calculator, and special adjustments for high-rainfall suburbs like the Mornington Peninsula, Dandenong Ranges, and outer west (190 mm/h). Whether you’re working on residential roofing, commercial gutters, or custom drainage projects, this guide ensures compliance and peace of mind.
1. Grab two numbers on site
- Roof plan area (m²) that drains into the box gutter
- Gutter length (m) between high points
2. Melbourne Quick-Pick Table
(Already multiplied by 170 mm/h and rounded)
| Roof Area (m²) | Max Gutter Length (m) | Kit Code |
|---|---|---|
≤ 60 m² |
≤ 6 m |
DB150-S |
61 – 125 m² |
≤ 6 m |
DB150-M |
126 – 190 m² |
≤ 6 m |
DB150-L |
191 – 250 m² |
≤ 6 m |
DB150-XL |
Gutter longer than 6 m? Split it and add a second kit.
3. One-line Calculator (if you like maths)
- L/S = Roof Area x 170 ÷ 360
- Pick kit whose **minimum flow ≥ L/s**
4. Real Melbourne job examples
- Richmond townhouse rear roof 45 m², gutter 3 m long → DB150-S
- Box Hill factory 180 m², gutter 5 m long → DB150-XL
- Camberwell double-storey 140 m², gutter 8 m long → DB150-L at each end
5. Outer-suburb tweak
- Mornington Peninsula, Dandenong Ranges, outer west: use 190 mm/h.
- Multiply roof area by 0.53 instead of 0.47 to get L/s, or just drop down one kit size (i.e. 180 m² in Rosebud = DB150-L instead of XL).
Call 1800 METFOLD (press 2) – we’re in Dandenong South and answer until 4:30 pm weekdays.