Rain Water Drainage

We are about to start work on our garden and need some advice on water drainage. At the moment all the guttering at the rear of our house (end terrace with conservatory) comes off the roof down onto the conservatory and into a water butt and that is where it stops. As soon as it rains hard the water butt fills up and starts to overflow onto our patio (why the previous owners did this is any ones guess, especially as there is no plants or lawn in the garden to use the collected water).

We are planning to take up the patio and decking and replace it with a lawn and re-lay a smaller patio area and want to direct the guttering into either a soak away of the mains drain.

Option 1 - Dig a soak away and have an over flow pipe from the water butt going into the ground (along with a small drain under the outside tap) and to the soak away. If we did this we would dig the hole about 5 meters from the conservatory. We have about 40 concrete breeze blocks and lots of shingle/rocks which were 'kindly' left behind by the previous owners which we could use to fill the soak away. We can also get a mini digger for making the hole. Is it just a case of digging a big hole, running guttering/pipes from the water butt/drain into the soak away and filling it back up with rubble and soil? How deep would we need to go? and is 5 meters far enough away from the conservatory to not cause any damage?

Option 2 - There is a mains drain cover just outside our bathroom where the conservatory joins the house. If we redirected the guttering to empty at this point would it be possible to drill down into the side of the drain and run the guttering out through that? I am a bit apprehensive about this idea as I would hate to cause structual damage to the drains (about a 6' drop to where the drains are) or allow the smell from the drains to escape into the garden. At the moment we have run a hose pipe from the water butt into the mains drain but even having the cover open an inch for the hose pipe lets a horrible smell into the garden at times.

Option 1 seems our best bet but any advice would be gratefully received. We are basically tearing the garden up and starting again and are planning on doing as much as we can ourselves to save money but at the same time don't want to get out of our depth and cause ourselves more problems further down the line.


  • stef73
    stef73 Posts: 545 Forumite
    First Anniversary Combo Breaker First Post
    We live in a terraced house, my soak away for the back is 1m cube. The soakaway is lined with a semi permable membrane then large bricks at the bottom going up in grades to 20mm pea gravel about .75m then the membrane goes over the top with drain pipe sticking out if it then soil and grass. Its about 30ft fron the house the drain pipe comes off the roof down wall and then slopes into the pipe in top of the soak away. All the calculations for size were done by architect who did the plans for our extension.
  • alwaysbrassic
    im not sure if i am reading it correctly but i dont think you can link rainwater to sewerage drains. We had this issue when we moved into our house, we were going to link to the waste pipe but we werent allowed, we had to dig a trench along the side of the house to pick up the other drains.
  • A.Penny.Saved
    I think that you might need 20mm aggregate, something which will hold water so it can drain away. The stuff which when filled in a trench will leave holes between the stones to hold water. The larger the holes the better IMO. It might need compressing so it doesn't sink over time.
  • rxbren
    rxbren Posts: 413 Forumite
    you cant join rain pipes to the foul pipes

    for your soakaway it needs to be at least 5meters from any buildings
    but before you can have a soakaway it all depends on he ground you need to dig a trial hole normally 1.2-1.5m deep and a suitable width to work in, once dug leave open for at least a day if there is water in the hole after this time a soakaway will not work

    you also cant fill a soakaway with soil as its the voids that hold the water and let it filter away

    only other choice is to find the original storm water drain which is propbably under your conservatory
  • southernsun
    Thanks for the replies.

    Is it a legal or practical reason why you cant join the foul drain? There is a drain cover in our garden which when opened has about 5 ft drop/pit to where our foul pipes from the house join a run away pipe for the rest of the row of terrace houses? If we had a rainwater pipe coming into the pit about 3ft down the water would just enter the pit and flow away. We wouldn't be attaching our pipes directly into any foul pipes just into the side of drain pit.

    I was beginning to lean towards this solution as it seemed like it would be a safer option (less likely to fail than a soak away).

    If we cant do the above then our new patio are will end about 6 meters from our conservatory. So if I dug a hole that is 1m deep, 1m wide and 1.5m long it would be 5m away from closest building but right on edge of the patio area. Would that be a big enough size?

    Also I was thinking milk crates might work in the bottom of the soak away as they would be strong and leave big areas open for the water to drain away, if I then put a layer of rubble (of various sizes) on top of this to bring this up to about 50cm then fill the hole in with soil and lay the patio over the top. Is this plausible?

    Sorry for all the questions, just been thinking about options the last few days and now getting confused.
  • jbainbridge
    Rain water / surface water should not go into the foul sewer ... in the event of heavy rainfall you don't want the foul sewer overflowing!!

    Everything you need to know about soak aways!
  • southernsun
    southernsun Posts: 435 Forumite
    First Anniversary Combo Breaker
    edited 20 September 2012 at 12:38PM
    Thanks for the link, the idea of using milk crates is the same as the Pre-fabricated cellular systems section, just when I looked into this those systems were several hundred pounds to buy and I guess from looking at other sites milk crates do the same job for cheaper.

    So my plan is now to follow the steps in the Pre-fabricated cellular system by digging a 1m deep, 1m wide and 1.5-2m long hole, put in 100mm course sand around all sides, fill hole with milk crates with something around them to stop soil getting in but allowing water to get out (same fabric used to stop weeds?). Then the rain water pipe fed into top of crates and finally fill the top 0.5m with soil and lay patio slabs over the top.

    Sorry few more questions:
    We are laying a new lawn about 4.5m wide and 12m long off the back of the patio, would the soakaway work better under the lawn than the patio?

    Does the above plan sound like it would work ok? (obviously I will dig a test hole first to make sure the ground can deal with the water ok).

    Is there any harm in adding rubble to the soak away? (We have 40 breeze blocks left over from when the previous owners had a wall built but not sure if these are suitable).

    Sure this makes no difference to running water into foul drains but the houses were built in 1908.

    Thanks again for all the replies and advice.
  • jbainbridge
    According to pavingexpert the soakaway needs to be atleast 5m from the building ... I guess the water could affect foundations etc.

    You crate idea sounds good. Not sure about the breeze blocks. The idea is to create a void which takes the water ... it then 'soaks away'!
  • southernsun
    Yeah I think the crates on their own should give the best results. Guess breeze block will just take up more room and add extra weight to the top of the crates.

    Regardless of if it goes under the patio or lawn it will be a minimum of 5 meters from our conservatory and 9 meters from the house.

    Think it is nearly clear in my head so unless someone replies with any warnings about the plans then I will dig a test hole this weekend.

    Thanks again for the help!
  • forgotmyname
    forgotmyname Posts: 32,575 Forumite
    First Anniversary Name Dropper First Post
    Wrong time to dig the test hole? We have not had much rain this month so far.

    If you can wait until we have had a few decent days of rainfall.

    Wouldnt work around here as the ground gets waterlogged very easily.
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