Please note: The Dimond lock seamed downpipe is not able to hold water at pressure or head and is not recommended for use with water collection systems under pressure or that carry water head pressure we recommend plastic, welded or seamless pipe if this is required.
Determine downpipe size. As a general rule for eaves gutters the downpipe sizes can be calculated as follows.
For circular downpipes:
- The cross-sectional area should be one half the cross-sectional area of the gutter.
For rectangular downpipes:
- The cross-sectional area should be one half the cross-sectional area of the gutter plus 10%.
Note: No downpipe shall be smaller than:
Circular downpipe
- 63mm
Rectangular downpipe
- have a cross-sectional area of not less than 3250mm2, and where the smallest dimension is at least 50mm.
Ensure that the downpipe size can be accommodated within the sole of the gutter.
Where rainheads and sumps are used both internal or external more accurate sizing of downpipes are achieved using AS/NZS 3500 Part 3.2.
Overflow
Gutter and downpipe systems must be designed to accommodate any overflows that may result in water entering the structure, regardless of where the blockage occurs.
One option for eaves gutters is to ensure the top of the fascia board or cladding finishes above the top edge of the back of the gutter, including at the high point. A gap should be created between the fascia/cladding and the back of the gutter. This provides a continuous emergency overflow regardless of where the blockage occurs.
For rainheads and sumps care must be taken to ensure the capacity of the overflow is equal to or greater than the designed flow capacity of the downpipe. In many situations the head of water above the downpipe effectively increases its performance, whereas an overflow of equal dimension to the downpipe has a slower flow capacity.
