How to ensure guttering fall with multiple downpipes?

[Isi]

Good morning. I am replacing old guttering. We have a 20m length of house with 2 downpipes. Question: does the fall need to be continuous from one end of the house to the other?

[Jewelleryrescue]

Hi @Isi 

Ideally you can put in a fall 1:20 as a guide.  But even if the gutter was flat that pro gutter guys make them at times evaporation will clear loose water out if a fall can't be introduced.

You really want to avoid pooling water in the gutter as that is a haven for mosquitos and dirt collection and therefore a mini gutter garden   later,

Hope this  helps.

[JacobZ]

Hi @Isi,

A warm welcome to the Bunnings Workshop community, it is fantastic to have you with us.

The National Construction Code Part 3.5.3 Gutters and downpipes states that "downpipes must not serve more than 12 m of gutter length for each downpipe". Being 20 metres in width means the gutter needs to discharge to two separate downpipes. 

I imagine the downpipes will be on the outside corners of the facade, so they would need to slope down from a high point in the centre.

The fall does not need to be continuous from one side of the facade to the other, they can be installed with a high point in the middle. This is known as a dual-pitched gutter.

You would likely need to order a custom gutter or have a roofing plumber create a custom connection to make this possible.

Let me know if you have any further questions.

Jacob

[elouisa]

In relation to down pipes on the corners of a 20 metre building would you not need another pipe in the middle, so the downpipes were not 20 metres apart only 12 or 10 in this instance?

[MitchellMc]

Welcome to the Bunnings Workshop community @elouisa. It's terrific to have you join us, and many thanks for your question about downpipes.

As @JacobZ mentioned, the high point would need to be in the middle, allowing water to drain to the downpipes on either end of the 20-metre span. You could add another downpipe in the middle, but that would then supersede one of the two downpipes on the outside, as one side would need to slope to the middle and therefore not allow one of the outside downpipes to collect any water. Typically, it would be best to slope to the outside and to the existing downpipes so that both sets of gutters are only servicing 10m of roof.

Please let me know if you have any questions.

Mitchell