2021 NCC Seminars: Can I use a chain downpipe?

This is a very common question. Can I use a chain downpipe? If you haven't seen this before, it's where instead of a downpipe you use a chain for water to run down.

We'll look at this from the perspective of Volume Two predominantly, but we will also cover Volume One. In Volume Two, the provisions are set out in the acceptable construction practice or ACP and Volume One refers to AS 3500.3 for the drainage requirements.

Now, AS 3500.3 is also an acceptable construction manual for Volume Two. In any case, whether you use the provisions within the NCC as we will step through in a moment, or AS 3500, the answer is the same. In the Volume Two ACP, the relevant provision is 3.5.3.5 sub clause has the details about the downpipe itself and sends you to these tables 3.5.3.2 through to.

Now in figuring out what downpipe you can have under the deemed-to-satisfy provisions, you have to start at the roof. Table a gives you a gutter type, depending on your rainfall intensity and the roof area. Even in my house, I've got type A gutters, which is good for my rainfall intensity and roof size and Table b describes what the various gutter types are.

Type A on my house medium rectangular with at least 65,000 millimetres squared cross-sectional area. And finally, you get to table c, which gives you the downpipes that you can use. Table c is here. And as you can see, chains aren't provided as an option. We've got only the conventional types that have listed in the column here in the left.

So you can't have a chain downpipe unless you do a performance solution. Relevant performance requirement is P2.2.1 in Volume Two and nothing here, and it's the same for Volume One as well and nothing here prevents a chain downpipe as long as the system takes the rainwater from a one in 20 year ARI storm to an outfall and keeps it out of the building. I do provide a word of caution though.

I mentioned earlier that Volume One deemed-to-satisfy provisions, send you straight to the standard AS 3500.3 and the standards an option also for Volume Two. Now in that standard clause 2.3.2 sets out the deemed-to-satisfy downpipes. It's almost a whole page of products and materials that the standard permits for downpipes and chains aren't one of them. Now at the very end of that clause is an informative note.

Now about notes in standards, these are informative. They don't have to be followed yet at the bottom of this page, the informative note simply reads chains should not be used as downpipes.

So can I use a chain downpipe? Well, not as a deemed-to-satisfy solution only as a performance solution. However, you may wish to take advice from those 3500.3.