drainage drop

[LSB]

Hi, I'm just thinking about drainage and I'm hopefully confused.

 

My understanding is that there should be a drop of 1:40 i.e. 25mm per m.

 

Our building is 25m long and has a toilet at each end and one in the middle with the treatment plant about 40 m away down a slope, so a drop of probably 2m across garden.

So, the total length from start to finish is 60 m.

 

This would mean that the drop should be 60m x 25mm = 1500mm  = 1.5m

For the house it is 25m * 25mm = 625mm so 0.625m

 

So if we start at 1m deep at the right then we need to end up @ 2.5m down for the perfect slope.

 

But, because of the slope of the land the treatment plant will be deeper than 2.5m from the start of the run.

 

Questions:

1. Does it matter if we go slightly steeper.

2. Does the drainage pipe have to be straight or can it be 1:40 past the house and then steeper to the treatment plant.

3. Should we be doing something completely different

 

TIA

Jill

 

 

Edited September 7, 2021 by LSB

[markc]

Going slightly steeper isn’t a problem especially with flush points at different locations as this will help to keep the line clear

[LSB]

and how many access points and rodding points should we have over the 65m

i.e. is there a set distance apart for them.

 

in our current house we do have some issues as the access to the cesspit goes under the road and over the years all the traffic has bent it.

this won't be the case with the new one, but we want to be able to access if necessary.

[markc]

I don’t know of any specific distance requirements but I assume each toilet will run out of the building to pick up a line running parallel to the build, in this case a chamber at each branch makes sense especially given the depth making intermediate rodding points a PITA.

[Mr Punter]

Don't start at 1m deep if you can avoid it.  Run the drains as shallow as possible allowing for the type of traffic above.  1:60 is acceptable for 110mm pipe.  This make inspection and rodding much simpler, as well as easier installation.  You can have the gradients steeper if you want to but if you change gradient you should have an access point.

 

The 40m from your last IC to the treatment plant is near the maximum but should be fine as you have plenty of fall.

[Temp]

1 hour ago, LSB said:

Our building is 25m long and has a toilet at each end and one in the middle with the treatment plant about 40 m away down a slope, so a drop of probably 2m across garden.

So, the total length from start to finish is 60 m.

 

This would mean that the drop should be 60m x 25mm = 1500mm  = 1.5m

For the house it is 25m * 25mm = 625mm so 0.625m

 

So if we start at 1m deep at the right then we need to end up @ 2.5m down for the perfect slope.

 

But, because of the slope of the land the treatment plant will be deeper than 2.5m from the start of the run.

 

Questions:

1. Does it matter if we go slightly steeper.

2. Does the drainage pipe have to be straight or can it be 1:40 past the house and then steeper to the treatment plant.

3. Should we be doing something completely different

 

 

Drains should be at least 300mm deep unless they will be driven over so perhaps start that deep.

 

Then 25m at 1:40 would go down 0.625m so the depth below surface is now now about 300+625 = 925mm.

 

Then you say the garden slopes down 2m over 60m..

 

60m at 1:40 would be another 1500mm fall but the ground slopes down 2000mm. So the depth below ground at the treatment plant would be 925 + 1500 - 2000 =  425mm

 

How deep does it need to be at the treatment plant?

 

Edited September 7, 2021 by Temp

[LSB]

2 hours ago, Temp said:

 

 

 

 

How deep does it need to be at the treatment plant?

 

we haven't finalised on which plant to use yet, still looking.

the treatment plant is going to be in one of the paddocks and not in the actual garden, but we don't want it sticking out above ground.

it will be fenced off so the horses don't 'play' on it.

[ProDave]

Is the paddock a wise place for a treatment plant?  Don't forget emptying, I doubt the tanker will want to drive into an unsurfaced paddock and risk getting bogged down in mud, so is there a surfaced track to get into the paddock and close enough?

[Gus Potter]

Hello LSB.

 

5 hours ago, LSB said:

Hi, I'm just thinking about drainage and I'm hopefully confused.

 

Don't worry, the confusion will wear off as you make progress, it's a learning curve, main thing is to enjoy the journey and drains are part of that!

 

Lot's of good info already posted here for you to digest.

 

To add a bit.. one helpful thing to do is to try and not make your treatment plant too deep under the ground. If you do then if the water table rises it has a tendency to float when you empty /clean it. Also, once you go below a certain depth (invert depth) for the tank it needs to be "stronger".. and these ones cost you more not just for the tank but the installation cost too. Your site (paddock) may have a slope so you need to make sure you can get the "Honeysuckle waggon" close enough and not too high above the tanks for cleaning. There is plenty info on the web from the tank suppliers, good laymans guides on this and how you comply with the regs in your local area regarding access, depths of tanks and water table level. You don't need for example to run the access road right up to the tank, but you can't have a bull in the field when the tanker driver comes..health and safety you see.

 

If you have long runs say from the garden out to the paddock then you could look at using 110mm diameter pipe locally around the house. Then do a straight run to the paddock in 150mm diameter pipe carefully laid. Here you could have a 1:80 fall, less even. The LABC allude to the fact that you could achieve a 1:150 fall with a 150mm dia pipe! Fine, maybe not for me at 1:150 on a self build type project but I would ask the treatment plant supplier to give you a 150mm inlet so you don't get a restriction at the inlet to the tank.

 

One way to figure it out is to draw it out to scale on a bit of say A3 paper.

 

60m run overall straight run say is not huge but it's still enough to make you think. I think with a little more research you'll find just the right solution for you.

 

Using the 150mm pipe for the long run means that you probably only need a few simple 150mm couplings which are fairly cheep comparitively rather than lots of expensive bends and funny offset bends etc . save these for the smaller 110mm pipe around the house.

 

 

 

 

Edited September 7, 2021 by Gus Potter

[LSB]

11 hours ago, ProDave said:

Is the paddock a wise place for a treatment plant?  Don't forget emptying, I doubt the tanker will want to drive into an unsurfaced paddock and risk getting bogged down in mud, so is there a surfaced track to get into the paddock and close enough?

we've thought about that and checked with the removal company.

what we are going to do is lay a track across the side of the garden covered with the plastic matts with grass and they will be able to reach the tank from there.

we considered a different place beside the drive, but decided against it as it is the opposite side of the house to the drains.

the location is also on the access to the barn for lorries when it was used for pigs.

thanks for the thought though.