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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorluz13827
    • CommentTimeOct 10th 2021
     
    Hello, I know this isn't necessarily 'green' related, but I know many on here have a lot of experience and knowledge, so worth asking! We are struggling to get an available plumber secured at the moment, so wanted to ask a few things just to help ensure we're on the right track before we proceed too far with builders.

    We are building a side return extension. There is currently an existing manhole in the side return. We plan to move this to the courtyard area shown in the proposed diagrams. The builders have done the hardcore and DPM and close to pouring the concrete sub slab. Can anyone help advise:

    - What basic work is involved in moving the manhole (the manhole is just for our house). We believe the pipes for the existing manhole run in a straight line to where the new manhole will go. Do we need to do anything with the existing manhole before we build over it?

    - Can waste pipes from the kitchen and downstairs bathroom area go above the sub slab? i..e either through or above the insulation (where the UFH pipes will be)? is there any issue with this?
      drains-01.png
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      CommentAuthordjh
    • CommentTimeOct 10th 2021 edited
     
    Manholes are usually placed where there is either a bend in the drain or a junction of drains. So the first thing to do is open the existing manhole and look where the drains come from and go to. Try e.g. flushing a loo or running a sink to prove that an input actually comes from that loo.

    The second thing to do is dig a hole where you propose the new manhole should go and make absolutely sure the drain actually runs under there!

    Given all the information you will then have you need to decide whether the proposed new arrangements will allow all the lengths of drain to be rodded. i.e. there's rodding access to all straight lengths of pipe. You will also need to know where any other manholes and rodding points are in order to do this.

    If you find that it's not going to work then you'll need to keep the existing manhole where it is and build it in to the new floor. It is possible to get suitable covers that mostly match floor coverings.
    • CommentAuthortony
    • CommentTimeOct 10th 2021
     
    I would change the existing manhole to a straight through one by using an upturned channel over its channel and grouting it in,

    Move all the connections, old and new into the new one, best under the slab laid to falls and tested.

    Cheapest might be to cut in a new preformed base with raising pieces.

    Not so much a plumber as drain layer

    It is possible to bury the existing manhole so long as each branch is rodable, inasvisable.
    • CommentAuthorluz13827
    • CommentTimeOct 10th 2021
     
    @djh - thank you! Sorry, a few more 'dumb' questions below.

    After we have hopefully confirmed that the drain runs under the new location, then is it fine for us to just build over the existing manhole (nothing more is needed with that)? Is it quite straightforward for new kitchen + toilet waste pipes to connect to the main drain at the new manhole location point? Is it OK for these waste pipes to be above the sub-slab (ie. in the screed) (we are moving the kitchen and bathroom points, so none of the existing waste pipes will be used).

    Can you just explain what you mean about the rodding - this is to enable any blockages to be cleared? Is it quite straightforward to add rodding access points to the pipe? Would anything limit whether it's suitable to add rodding access here?
    • CommentAuthorphiledge
    • CommentTimeOct 10th 2021
     
    If you are going to build over the section of drain from the courtyard to the existing manhole and beyond, I would get the drain camera inspected! Once its buried under your new kitchen itll be very difficult to carry out any repairs if the drain is or becomes defective.

    If its not too deep it might be worth digging it out, renewing and encasing it in concrete. Im not sure whether its still the case but I think it used to be a requirement to expose existing drains under new buildings and encase in concrete??

    The shape of the building on your plan suggests it could be a terrace house and if thats the case I would double check that the existing manhole isnt covering the junction of your drain to a common drain serving the neighbouring houses??
    • CommentAuthorluz13827
    • CommentTimeOct 10th 2021
     
    @philedge - thank you - we are planning to reroute all of the drains to the new location, so I think that section between existing manhole and courtyard would be redundant.

    My partner who has been onsite said it's a private manhole/not shared with neighbour, however will ask for that to be double checked.
    •  
      CommentAuthordjh
    • CommentTimeOct 10th 2021
     
    Posted By: luz13827@djh - thank you! Sorry, a few more 'dumb' questions below.

    After we have hopefully confirmed that the drain runs under the new location, then is it fine for us to just build over the existing manhole (nothing more is needed with that)? Is it quite straightforward for new kitchen + toilet waste pipes to connect to the main drain at the new manhole location point? Is it OK for these waste pipes to be above the sub-slab (ie. in the screed) (we are moving the kitchen and bathroom points, so none of the existing waste pipes will be used).

    It all depends what's inside the existing manhole and you need to know what it is as a fact, not as a supposition. I think you need to make two plans: one showing all the existing drains on your property with manholes and sinks, loos etc marked, and the other one showing the proposed new arrangements again with all manholes and sinks, loos etc.

    Then as Tony says you need to find a groundworker who specialises in drains, and you'll probably also need a regular plumber if you are installing new sinks etc. As Phil says you need to make sure that any existing drain is in good condition and protected.

    Can you just explain what you mean about the rodding - this is to enable any blockages to be cleared? Is it quite straightforward to add rodding access points to the pipe? Would anything limit whether it's suitable to add rodding access here?

    Yes rodding is to enable blockages to be cleared. There has to be a manhole or or other access to allow a set of rods to be put down each straight length of drain below ground. I can't remember what the rules are about altering drains. I know when we built we needed groundworkers with water board approval to connect the drain to the public system and our plumber was also water board approved which meant he could self-certify the plumbing. Otherwise we would have had to pay for a water board inspector to come and check it all. So please check the rules.

    I strongly recommend that you get professional help and don't try to do anything yourself. You might be able to help with digging etc once it's decided what needs to be done.
    • CommentAuthorphiledge
    • CommentTimeOct 10th 2021
     
    Posted By: luz13827@philedge - thank you - we are planning to reroute all of the drains to the new location, so I think that section between existing manhole and courtyard would be redundant.


    If that section is to become redundant then doesnt the existing manhole become redundant? In that case just fill it with concrete and flood the redundant section of drain with concrete to ensure it doesnt collapse and leave a void under the extension floor. If you have a general builder on site I would have thought he should know all this??
    • CommentAuthortony
    • CommentTimeOct 10th 2021 edited
     
    Drains should go under slab, small 32mm or 40mm pipes can run in screed but best not.
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