Downpipe Options

Downpipe options are many and varied.

As a standard round in 80mm diameter, in prepainted coil steel of ColorCote MagnaFlow (formerly ZM8) and Zincalume. Standard lengths are 3.2m long. Other lengths are subject to confirmation. Call 0800 DIMOND.

Spiral welded pipe (not supplied by Dimond) can be used on large commercial jobs especially where the downpipe passes through the building, resulting in a “pressurised” downpipe system.

Dimond does not recommend using their fabricated lock-seamed downpipe, such as is used on the rectangular or round shape in enclosed ceiling spaces and wall cavities.

115º round zinc elbow bends are available in standard colours for connecting the standard 80mm diameter downpipes together. The joint with the downpipe must be sealed and held with a minimum two 3mm aluminium rivets to each joint.

Copper A similar range of sizes are available. Call 0800 DIMOND to confirm availability. The material is suitable for use where bends are required as the product can be mitre cut and the joint soldered. Zinc elbow bends must not be used due to dissimilar metal contact.

Other materials subject to confirmation. Call 0800 DIMOND.

System Design

System Design

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.

Note: No downpipe shall be smaller than:

downpipe 63mm (nominal available size is 80mm dia)

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.


Downpipe Installation

Determine the offset length

  • Measure from the bottom of the gutter to the bottom of the fascia board. This is measurement A (fig 1).
  • Cut a piece of downpipe to a measurement A and place it onto the dropper with an elbow, see fig 2.
  • Measure from point C on the elbow to the wall of the building see fig 3. This becomes measurement B. Then deduct 120mm from measurement B to allow for the elbow and standoff from the wall. For example if measurement B is 600mm, the length of the downpipe required for the offset is 480mm long.
  • When assembling the offset use a neutral silicone sealant making sure that there is a continual ring of sealant up against the stop inside the elbow and another ring 10mm from the outside edge of the elbow.
  • Place the first downpipe bracket under the elbow to retain in place then continue to attach the downpipe to the wall of the building using three downpipe brackets per downpipe.


  1. Dimond does not recommend the use of downpipes in wall or ceiling cavities
  2. Dimond downpipes are specifically designed for use with Dimond fascia and gutter systems.
  3. To ensure a water tight fit we recommend using only Dimond accessories when installing metal downpipes.
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