# Forum Home Renovation Plumbing  Advice on burying stormwater pipe

## Vernonv

Hi All,
I'm looking for advice/information on the best way to bury a stormwater pipe. 
The pipe will be going under our driveway (gravel) and will probably be no less that 1 foot below the surface. The pipe will be going to a water tank. 
We only get light vehicles on the driveway (cars and possibly a 4WD - no large trucks, etc) 
What size/class pipe should I use - will normal 90mm be OK?
Should I encase the pipe in concrete - or should I just surround it in sand and then backfill? 
Any and all advice appreciated.

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## Terrian

> Hi All,
> I'm looking for advice/information on the best way to bury a stormwater pipe. 
> The pipe will be going under our driveway (gravel) and will probably be no less that 1 foot below the surface. The pipe will be going to a water tank. 
> We only get light vehicles on the driveway (cars and possibly a 4WD - no large trucks, etc) 
> What size/class pipe should I use - will normal 90mm be OK?
> Should I encase the pipe in concrete - or should I just surround it in sand and then backfill? 
> Any and all advice appreciated.

  90mm stormwater pipe is fine, but I would be going deeper than 300mm (actually, I did go deeper, 900mm, but I have a mate who has a small back hoe, here he is trying to knock down my garage (please note, custom built garage  :Smilie:  ) [ame="http://www.youtube.com/watch?v=ejAxk9PX96I"]LINK[/ame]  
anyways, I would not go less than about 500mm depth for pipe that is likely to have vehicle traffic, other option would be to dig the trench 400mm deep, 350mm wide and lay 270mm concret pipe, and slide your 90mm stormwater through that, then just backfill the trench with sand, and top over with crushed rock.

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## Barry_White

I think 300mm to the top of the pipe will be fine provided the trench is kept to just clearance at the sides of the pipe because there wouldn't be much pressure on the top of the pipe. I have seen storm water pipe at less depths without any problems.

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## Vernonv

Thanks Guys. 
So Barry, what your are suggesting is to only have the trench wide enough to fit the pipe? 
Should I surround the pipe with sand (or similar material) before backfilling or doesn't it matter? 
Terrain - my shed it coming along nicely - will be good having 7.5 x 12 of workshop space and another 3 x 12 covered area for storage (awning off shed). I should post some pics up.

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## Terrian

> Thanks Guys. 
> So Barry, what your are suggesting is to only have the trench wide enough to fit the pipe? 
> Should I surround the pipe with sand (or similar material) before backfilling or doesn't it matter?

  What Barry says is true, to a point, if the ground is very stable, ie: bloody near rock hard to dig, 1/4 minus (7mm) stone around the pipe.   

> Terrain - my shed it coming along nicely - will be good having 7.5 x 12 of workshop space and another 3 x 12 covered area for storage (awning off shed). I should post some pics up.

  7m wide x 6m deep is my garage, 6m x 6m shed going in behind it (at some stage  :Smilie:

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## rsser

Wouldn't hurt if you had some gravel or scoria to lay it in and to put over it.  That's a requirement where I am with PVC sewer pipes even if they're 3m down.

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## bricks

I normally use 100mm sewer grade pipe, it's stronger and much more suited to rodding if it ever gets blocked.

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## Barry_White

> Thanks Guys. 
> So Barry, what your are suggesting is to only have the trench wide enough to fit the pipe? 
> Should I surround the pipe with sand (or similar material) before backfilling or doesn't it matter? 
> Terrain - my shed it coming along nicely - will be good having 7.5 x 12 of workshop space and another 3 x 12 covered area for storage (awning off shed). I should post some pics up.

  I have stormwater pipes that are only about 2 inches under the ground that are in Granite sand that have been there for 20 years that I have driven my ride on mower as well as my Toyota Hilux over with out any damage so I would suggest using some sand around the sides and an inch on the top and refill with the natural soil dug out of the trench but dig the trench with very little clearance around the pipe.

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## Rossluck

I'd basically go just a little deeper (two foot) or put a bit of concrete over the top of it where it goes under the driveway. This is simply because, after heavy rain (remember it?) when the ground is waterlogged, a heavy vehicle can sometimes have a wheel sink down and crush them. This happend to me when my brother drove his Land Cruiser over mine. 
If you can keep them well below what a vehicle's wheel would reach in a bog, you should be OK.  :2thumbsup:

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## Vernonv

Thanks for the input everyone. 
Rossluck - the ground where the pipe is going is pretty well compacted and we have never had any issues with it getting boggy, etc. 
Thanks for clarifying that Barry - sounds like the way to go. 
Bricks (I was wondering when you were going to post) - can you get fittings to go from 90mm stormwater to 100mm sewer. Also I saw somewhere that there is a heavy duty version of the 90mm stormwater - would it be any good?

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## Terrian

> T
> Bricks (I was wondering when you were going to post) - can you get fittings to go from 90mm stormwater to 100mm sewer. Also I saw somewhere that there is a heavy duty version of the 90mm stormwater - would it be any good?

  pretty standard fitting, 100mm to 90mm adaptor, bunnings sell them , as would almost any place that has plumbing supplies (even your local garden supplies is likely to have them.

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## bricks

You can buy fittings to go from 90mm stormwater to 100 mm pvc, conveniantly it called a 90mm stormwater to 100pvc adaptor, ( not taking the piss mate, that's what its called). 
For some reason you can get sqaure downpipe- 90 stormwater, but not to 100 pvc. But you can adapt after. 
The thicker stormwater pipe i've not had anything at all to do with, I'll be honest mate i'm a stubborn git at times, and not using stormwater grade pipe is one of my quirks. So as for if it's good? I cant honestly tell you.  
When you dig the trench make the trench 100 mm wider and deeper and fill with sand to 100 above the pipe. This will stop little rocks punching through the side of the pipe when you backfill. If when you dig the trench the dirt is reletively loose and fine, Not in clumps bigger than around 20mm of dirt and there arn't a noticeable amount of rocks, you could probably get a way with using the same stuff as backfill. 
To work out how much backfill you need- 
Length x width x height ( in meters.) x by 1.8 will give you the approximate tonnage of what you need to order. :2thumbsup:

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## wonderplumb

The 100mm stormwater pipe, if you can find it seems to be ok as far as stormwater pipe goes, has a similar wall thickness to the 6" stuff. You dont see it much here in sydney but Im with Bricks as far as the 90mm rubbish goes, better off spending the extra and buying 4"sewer (DWV) pipe and fittings, it will save you in the long run.

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## Vernonv

Thanks for the additional info guys.  
Ok, so I'll go for the 100mm sewer and make sure that I surround the pipe in sand (thanks for the formula Bricks).

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## bricks

You can change the down pipes to round Pvc Eg; 65mm for easy hook up to underground system too.

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## trover

I would also suggest a drain point for a wet system, to drain out the dust every now and then. Thats a screw on lid on a tee piece, of instead of an elbow. Good luck with the digging.

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## Vernonv

Trover - yeah I was planning to do that at the point where the pipe goes "up" to the water tank inlet. I will use a T piece with a screw fitting on one end of the T bar. 
Bricks - I'm not quite sure I understand why I would want to use 65mm downpipe (I'm sure I'm missing something here :Confused: ). Wouldn't it be better to use the biggest possible pipe size  - I was planning on using 90mm from a leafbeater down to 100 sewer for underground and then 90 back up the the tank inlet.

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## bricks

What I'm getting at is that if your changing from stormwater grade to pvc grade pipe your going to have to buy an adaptor, If you keep all the pipe grade type the same eg all Pvc then you will be able to use available fittings to connect your down pipes to the system. 
Everytime you change pipe it will have a small cost associated with it.
Every time you change its another fitting that you need to install neatly to look nice- not easy if you don't have much room. 
65 pvc might be okay, but whoever sold you the shed / roof should be able to give you the correct size for your area.  
If your going to a large pipe size for the down pipes i'd use 100mm pvc as it (more often than not) is cheaper than 80mm pvc. Pvc is thicker and therefore won't be damaged as easily by things hitting it. you will need to paint the pvc to prevent it from becoming brittle in the sun. 
Or you could bring up 100 pvc to about 250mm above flood level and then run a standard square down pipe into it, That way you won't need a fitting at all. You would need to ensure the pvc is raised to above the outlet of the stormwater system.  
To make a long story short....... :Wink:  
Install a downpipe of any material 
Lay the 100mm sewer grade pipe as you were going to,
Bring up 100mm risers where the down pipes are,
Run to tank as needed,
Make sure the downpipes have stopped above the level of the inlet of the tank, and that the 100 pvc over-laps by about 50mm. 
This way if the system does ever block up between the tank and the gutter the overflow will be from the downpipes around the outside of the house, not the gutters and back into your shed / house. 
Hope that helps,

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## Vernonv

Thanks Bricks, that clarifies things.  
Also thanks for the additional info - I hadn't really considered what would happen if things blocked up.

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## bricks

No worries bloke, I just hope you realise im not the best communicator with the written word, hoping im not coming off as an arrogant know it all.  
Let us know how it goes anyways 
Cheers.

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## Vernonv

Bricks, I haven't taken the delivery of any of your comments, suggestions or information as being arrogant. And greatly I appreciate your input, as well as that of the other contributors.  
I let you know how I get on (with pics, hopefully), but it may be a while as it will take approx 2 months to get the tanks (must be all these Sydney people buying water tanks and pushing up demand :Rolleyes: ).

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