Raising floor (Pouring concrete) over drain cover and toilet hole

Discussion in 'Plumbers' Talk' started by Dr.P, Jul 6, 2016.

  1. Dr.P

    Dr.P Member

    Hi,

    I have a lean-to attached to the side of my house. It's an old 40's house so the lean-to had a toilet in there.

    My plan is to convert the lean-to into a small extension and indoor toilet. My first job will be to raise the floor 150mm to the same level as the house. My problem is that there's a drain cover and the toilet hole currently in the way. I want to know how I could extend the toilet drainage hole up to the correct level. And what do I do with the drain cover? I can't just concrete over it, can I? I think it's a sewerage cover.

    Thanks.
     
  2. KIAB

    KIAB Super Member

    You can use a piece of plastic soil pipe to raise it to use toilet again,easily enough.
    Two options with manhole,one it's just a simple job of a couple of courses of engineering brick to raise the height, then use a double seal recessed manhole cover.
    Other way is to relocate manhole if feasible outside of room, no need to use a DS manhole cover then.

    Did identical job here,raise floor 150mm from back door to & including the outside toilet, as there was no damproof membrane under exsisting concrete, I just gave exsisting concrete floor & wall up to the dpc two coats of a liquid dpm,& also put down 50mm of celotex has I happen to have some laying around.
    Nearly 7 years on & not a sign of any damp coming up through the concrete.:)
     
    Last edited: Jul 6, 2016
    Plumberbish likes this.
  3. This drain cover - is it a blank access cover, or is it a grate to allow water to drain down?

    If it's a 'grate' and is no longer required and if you have adequate access to this underground pipe for rodding etc elsewhere, then it should be ok to simply cover it permanently.

    If.

    Anyhoo, why would you wish to 'concrete' this floor? Surely a timber joist floor with insulation would be a far better choice?

    DPM, small concrete 'pillars' (blobs...) to get the joist bottoms to the correct height and dead level, joists on top, noggined, filled with insulation and ply or chipboard on top.

    Cosy as a cosy thing.
     
    KIAB likes this.
  4. KIAB

    KIAB Super Member

    Cheaper a supended floor.:)
     
  5. And a lot colder :p
     
  6. Dr.P

    Dr.P Member

    OK, so a suspended floor will be cheaper and warmer? Sounds good to me.

    What would I use? 6x2, kingspan in between, then ply on top?

    The drain is a service drain for my sewerage and there's no other access, so I'll have to some sort of cover for that and incorporate it into the tiles. Recessed manhole cover sounds good as well.
     
  7. Sounds like you'll need to keep access to that cover right enough. You'll chust have to design a hatch for this, which can be semi-permanent. Eg - make a frame around the existing drain cover to the same height as the rest of the floor joists (ie - using the same timber). And then make the flooring board above an access hatch - cut the chipboard so's it sits half-way over the top of the joist frame, and secure with screws. I wouldn't even worry about cutting and shaping the DPM at this point as that can be done in the future in the unlikely event of you having to access the drain cover, and then it can be made good with DPM tape afterwards.

    Ok, this is what I would do... Lay a DPM over the ground, making sure there's no sharp bits that could damage it. Good chance you can put down two layers as the area isn't large and the sheets tend to be.

    Lap it up the wall to comfortably above floor height. Ideally you'd take it a good couple of feet up the walls, but that depends on whether you are adding new wall boards afterwards? If not, take it to above skirting level for now and it can be trimmed afterwards.

    Then work our what size joists you'll need to raise the level the right amount, bearing in mind a chipboard layer on top (at least 18mm thick) and any other floor coverings. You'll likely have a choice of 4x2 or 6x2 (do they make 5x2?!)

    Personally, I'd use rough sawn treated timbers for this, to be sure to be sure.

    Ok, space them at 400mm centres, and work out how far they need raising to level them and get them to the required height. I'd then mix a stiffish (not sloppy and wet) batch of concrete - aggregate and cement - and plonk down a good trowel-full every foot or so along where each joist will run, and gently tap each joist down into it until it's nicely bedded and at the perfectly correct level. If you think it'll be easier, then you could make up the joists as a frame first outside, with noggins nailed in between them so's you can lay it down as one 'section' (or even two halves). Then tap the whole section (or half section) down in one go.

    The joists can stop short of the walls by an easy inch each end, so plenty or 'play' room if needed. (In fact make sure the joist ends don't tear the DPM in the wall corners as you lay them down...)

    Any wiring or plumbing to be laid under the floor, do it now...

    Ok, that'll give you the best part of a 5" underfloor void to fill? I would simply use 'Jablite' which is white expanded polystyrene insulation sheet - it's cheap, easy to cut, and available in various layers.

    Simple trim then into widths to fit down into the spaces between the joists until they are filled up to top-of-joist level. (Wait for the concrete to set first so's you don't disturb it whilst doing this...)

    Jablite is fine here 'cos the amount of insulation you need under the floor is minimal compared to walls and ceiling. (I am assuming you are DIYing this job and not involving building regs...?)

    And then screw down your chipboard flooring on top.

    That's what I did to the room I'm sitting in now - which was an attached garage. My 'joists' ranged from 6" to less than 2" due to the sloping garage floor, so I have less than 2" of Jablite at one end. Floored using softwood T&G. It's the cosiest room in the house :)
     
    Last edited by a moderator: Jul 8, 2016
  8. KIAB

    KIAB Super Member

    You could still raise the manhole a few courses, so the recessed manhole cover finishes at same height as finished floor.:)

    Depending on the manhole setup, might be easier & possible to relocate it outside the room.
     
  9. Dr.P

    Dr.P Member

    Now that is the most comprehensive reply I have ever had. I'll go ahead with the wooden floor I think. Thanks for all the input.
     

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