Downpipe Size in Melbourne (2026)
In Melbourne downpipe sizing follows the roof area feeding each pipe and the local rainfall intensity, which set how many pipes and what diameter.
How we estimate this
Downpipe sizing follows AS/NZS 3500.3 and depends on the roof area draining to each pipe and your local rainfall intensity, not just the roof size. As a rough guide, one standard 90 to 100mm downpipe handles a modest suburban catchment, and large roofs need several.
Pricing reviewed: October 2026.
What a downpipe size costs in Melbourne
Working out downpipe sizes for a Melbourne roof starts from how much roof drains to each pipe and the intensity of a heavy local rain event, since a downpipe has to clear the peak flow from its slice of the roof, and the plumbing code converts that catchment and that rainfall rate into a diameter and a count. A larger roof under a heavy burst needs more downpipes or wider ones, so dividing the roof into catchments and applying the local intensity is the core of the sizing.
Melbourne's rainfall is steadier and generally less intense than the subtropical north, but a summer storm still produces a peak the pipes must handle, so the sizing uses the local design intensity rather than the gentle winter drizzle. A Victorian or Edwardian period home with ornate guttering is matched with downpipes sized for its roof area and sympathetic in style. Reactive clay around the footings makes it important that downpipes discharge well clear of the foundations, which the stormwater design handles. The roof plumber sizes and fits them to the plumbing code, and competitive trade labour just below Sydney's keeps the work reasonable.
Downpipes are roof plumbing sized and installed by a licensed roof plumber to the plumbing code, connecting to the stormwater system, in Victoria under the Victorian Building Authority. For a Melbourne roof, the clearest way to size downpipes is by the roof area feeding each pipe and the local rainfall intensity, which set how many pipes and what diameter, with discharge kept clear of reactive-clay footings.
Compare against the national picture: Downpipe Size in Australia →
Downpipe Size in other cities
Frequently asked questions
How are downpipes sized in Melbourne?
By how much roof drains to each pipe and the intensity of a heavy local rain event, which the plumbing code converts into a diameter and a count, so a larger Melbourne roof under a burst needs more or wider downpipes.
Does Melbourne's rainfall change the sizing?
Yes. Melbourne's rain is steadier and less intense than the subtropical north, but a summer storm still sets a peak, so the sizing uses the local design intensity rather than the gentle winter drizzle.
Why keep downpipe discharge clear of footings in Melbourne?
Because reactive clay around the footings swells with water, so downpipes discharge well clear of the foundations, which the stormwater design handles to protect a Melbourne home from footing movement.
Do I need a licensed trade for downpipes in Melbourne?
Yes. Downpipes are roof plumbing sized and installed by a licensed roof plumber to the plumbing code, connecting to the stormwater system, in Victoria under the Victorian Building Authority.