Guttering fall?

[flanagaj]

Our tech architect has specified a single downpipe for the 17m long roof.  I am just worried that over a 17m run it will be too low and the water will come off the roof and miss the guttering.  I did search online for recommended fall, but my confidence in the internet was dashed when I read the below recommendation 🤣

"

The ‘fall’ is the measurement by which the gutter drops to allow water to drain towards the outlet downpipes.

Many plumbers guidelines recommend a ratio of around 1:500 (which is roughly 20mm for every 5m of guttering). But it does depend upon the pitch and size of the roof above your guttering.

"

[crispy_wafer]

downpipe at one end or in the middle of the run?

[bmj1]

I'd personally do two downpipes, one at each end. Pretty sure that's what we did on ours with a 13m long roof

[markc]

2 down pipes is always preferred in case 1 gets blocked, or if at 1 end and very heavy rain the furthest end can fill and overflow but 1:500 is plenty for a gutter.

[Russell griffiths]

2 down pipes and very very little fall even dead flat, you don’t need much fall with modern aluminium gutters or high flow gutters. 
 

the weather in this country is changing, gone are the days of 8 hours of drizzle, now it’s. Big fat rain drops, these people specifying this stuff need to stop thinking it’s 1886. 

 

Australian regs are an outlet every 6 m, you want the water off the roof not sitting in a gutter unable to get out. 
we are starting to get more tropical big weather events. 
 

I would never build anything again with either hidden gutters or box gutters, recipe for a disaster. 

Edited August 11 by Russell griffiths

[saveasteading]

3 hours ago, Russell griffiths said:

hidden gutters or box gutters, recipe for a disaster. 

 

With one client whose architect would not contemplate external gutters, and with only the end available for outlets, I doubled up on outlets, ie a full gutter would flow over one to the next one.

On another we  took the gutter out through the gable to a big hopper with external dp, and with an overflow wier... so any freak rain would overflow outdoors.

 

Once the water is in the downpipe it will cope easily, its the entry to the dp that is restricting.

 

ie overdesigned acc to the regs.

I imagine and hope that they coped with this year's downpours.

External gutters are good and why hide such an important feature of a building?