# Forum Home Renovation Plumbing  Stormwater pipe questions

## Human Potato

Hi Guys, 
I am about to (in the next month or three) start working on the storm water drainage for my house. Currently 3 of the 4 downpipes dump water directly onto the ground, some uphill from the house, and only one of them leads to the gutter on the side of the road. It is my cunning plan to run storm water pipe to this same outlet and feed all of our stormwater into it.
A picture is worth 1000 words, so here it is:   
Now, my questions:
1) can anyone see any immediate problems with me doing this?
2) for my underground pipe, what should i use? Bunnings has 90mm and 100mm. The 100mm feels a lot stronger, but usually when talking about storm water people discuss 90mm. Considering how cheap it is I don't mind which I use, but what is the correct choice?
3) I would like the aboveground pipe to be as inconspicuous as possible so I would like to use smaller than 90mm pipe for this. Is it true to say that any pipe that has been painted in exterior UV resistant paint will be safe from the sun?
4) The underground pipe will be underneath an area that has already been concreted over. I intend to cut "slabs" into the concrete to gain access. What is the minimum depth I should aim for running the pipes? The area will only ever have irregular foot traffic (it will end up having a deck over it). It will never see any vehicle traffic. 
Any advice would be appreciated.

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## chrisp

My advice (not that I know much about this):  Use 100mm pipe - especially underground.Do you have under-house access?  If, so, consider running the pipes under the building instead.

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## andy the pm

Like Chrisp says, use at least 100mm for as much as you can, at least from pit 1. 
What dia. is the existing pipe to street? 
The thing you have to bear in mind is that during periods of heavy rain you may overload your pipework and your gutters may overflow. I'd be inclined to split the system, one down the left side (of the drawing) and one down the right and out a new outlet into the gutter. 
But thats just me, and I'm not a plumber...but I do have one either side of my place

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## sundancewfs

Definately use 100mm ( We used 150mm for a very big roof )

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## Compleat Amateu

Maybe the plumbers will come in here, the right answer to size is a rainfall intensity calculation, which is essentially rainfall intensity for your area (from Bureau of Meteorology or Engineers Australia) x the area you are trying to drain.  I suspect it's all in BCA, though never had to look! 
Having said that, 4 points worth bearing in mind:
a) Do you have a friendly neighbour uphill donating their stormwater to you?  Or a big back yard doing the same thing? If so add to your calculation and think about how the runoff is going to get into those pits;
b) You say "little pits", I say BIG pits, the right ones are about 450 x 450 x 450, can't remember exactly.  Reln make them, and probably others;
c) Don't use 90mm in ground, it ain't tough enough, doesn't matter if it meets the above requirement;
d) As said above, create a second street outlet.  Why take stormwater right around the back of the house?  Also the second outlet obviously double your total capacity at the pint where it starts to matter. 
Cheers 
Compleat

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## wonderplumb

Is there a reason why you want to externally hang the 'red' pipework in your drawing?
Your drawing is good and the pits at each corner are a good idea,
Could you, 
a) Take DP#3 into PIT#1 then take an outlet from PIT#1 into another pit at DP#4, put DP#4 into this then take an outlet from this pit out to the street
b)take DP#2 into PIT#2, take an outlet from PIT#2 down into PIT#3, run DP#1 into PIT#3 then take an outlet from here out to the street? 
1) Where you install a pit, be sure to run everything into and out of said pit rather than marry them together underground before the pit, 
2) Use 100mm pipe and be sure to use priming fluid also
3) If you need to hang pipe externally you can use 90mm as it tucks in a bit tighter and neater than 100mm, bracket it at every 1200 and painting will look after it, if you can go underground use 100mm.
4) 450 x 450 pits, as compleat suggested would be the way to go aswell, the reason for terminating things individually into the pits is for cleaning access, this will allow you to clean each and every bit of pipework.

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## DMAK

After having just backfilled last sunday night, about 20m of drains, I've just read this thread...  Sooo.... Is it me or do I miss something, how can you have downpipes coming off the roof, connect to stormwater pipes underground, that have pits and grates on them? 
Wont the water falling 3-4m off the roof just come out the grate and just flow over the ground?  Or do we just assume there's enough fall in the ground from the back of his house to the gutter on the street to "pull" the water out? 
At my place, there's only 150mm fall from the bottom of the trench I dug to the gutter on the street about 40meters away - pretty flat huh!?!  There is only 400mm fall from the to of the patio cement slab at the back of the house to the gutter on the street (don't need to be a rocket fixer man to figure out I didn't dig deep trenches...) :No:   
The reason I asked about the pits and the downpipes and the fall, and it flowing out into the yard is because I'm about to set a second trench from the back of my house to gutter on the street for the ground level drainage, with pits and pipes.  But I just assumed I couldn't mix my downpipes with open air pits. 
I shold also add I live in Mackay QLD where it can really rain!

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## duncang

Hi DMAK, 
I'm in a pretty similar situation to you by the sounds of things in terms of lack of fall on my block.  I'm in Brisbane. 
Last weekend I dug up the storm water pipes (wondering why they weren't draining) to find broken pipes, so this weekend they're getting replaced.  I've also just dug a rubble trench down the side of the back yard for drainage.  
My plan was to run the aggie pipe (socked) from the rubble drain into a pit (more or less equivalent to Pit #2 in the OP's drawing) and then that is all connected to the stormwater drain to the street.  Is this OK or should I run a completely separate pipe for the rubble trench drain? 
Thanks,
Duncan

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## DMAK

Hey Duncan, I don't know what happened to everyone, but they all seemed to shy away from answering when I mentioned not joining ground level drains with roof releaving downpipes. 
In my mind on "almost" flat ground, you couldn't mix the two systems, otherwise the water from the roof will just come out the drains, rather than go to the kerb side gutter... 
Path of least resistance or something...

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## Human Potato

Hi DMAK 
I don't know if you are still following this thread, but in case you are... 
The basic premise of my design is that every single pipe in the diagram is sloping downwards, so gravity will be responsible for removing the water from the system. The purpose of the pits at each corner are primarily for inspection and cleaning of the storm water pipes, rather than for collecting any surface water, and all the pits will be connected to the underground pipes, so the only time the pits would overflow would be if the water volume exceeded that which a 100mm pipe can feed. 
I intend to have the downpipes dropping water into grate-covered pipes that lead into the stormwater pipes. The reason I dont want to connect the down pipes directly to the under ground pipes is in case the underground pipes become overloaded. I would rather have the water overflowing onto the ground outside that to have my gutters fill up and then flood my roof. However, I doubt that the pipes would ever become overloaded in my region, I guess your rainfall would be much greater than we experience in Canberra. I have watched the water coming out of my downpipes during the heaviest downpour and I have no doubt a 100mm pipe will be able to handle all of them combined. 
Also in my case, most of the underground piping will be covered by concrete so I will not be laying the pipe very deep (there is no vehicular access to these areas). This will allow me to ensure there is always a downward slope to all parts of the system because the shallower your "pipe run" begins, the deeper you can make it later on to create slope. The area between Pit #1 and Pit #2 is roughly level, so I will have to dig a slope for this run. The area between Pit #2 and Pit #3 is all downhill, so I will just have to run the pipe at a constant depth to achieve a slope. Downpipe #4 to Pit #1 is actually UPHILL, which is why i will need to run the pipe above gound along the outside of my house, so that I can make it run downhill, i.e. the downpipe will connect to the pipe about 1m above the ground, and by the time the pipe reaches Pit #1 it will actually just be reaching ground level (the pipe will be sloping down while the ground is sloping up). I hope i haven't just added to the confusion. 
Someone asked why I don't just run a second stormwater outlet to the street. That would be great but I imagine I would have to involve the council in taking such an action? I have no doubt I could do it perfectly (famous last words of many a DIY'er :Biggrin: ) but I am allergic to council involvement in my house, and I would rather pull my eyes out than to spend money on paperwork and fees for which I get nothing in return. I think if they laid eyes on my house they would instantly order that it gets bulldozed  :No: . Has anyone else run their own stormwater outlet to the street?  
Let me know if you have any other questions or suggestions, it is still in the planning stage. 
Anyway, I have scheduled the job for my Xmas holidays, I will keep you all posted....

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