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Drainage regs - shared 110mm soil pipe branch with basin, ok?

Discussion in 'Plumbing and Central Heating' started by DIYAmelia, 23 Jul 2021.

  1. DIYAmelia

    DIYAmelia

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    Hello,
    I am currently replacing the external 110mm soil pipes during a bathroom renovation.

    Q can I use a strap on boss to connect the basin bathroom waste, 32mm solvent weld, entering 45 degree from vertical , to the 110mm soil WC waste branch via strap on boss, rather than to the vertical stack vent from side? See PICTURE.
    I have put everything in place but not fixed in place etc

    Drainage Regs H don't seem to mention this explicitly.

    I'm aware pan connectors are sold with a 40mm fitting, similar to what I am suggesting, except interior to building rather than external. I am worried about gurgling noises / suction when toilet flushed as toilet flush passes by basin outlet. Unfounded?

    I could drop the vertical 110mm stack to allow connection above the WC branch, might be under 20cm vertical allowed between branches/connections on same side of stack and seemed to put the branch under strain.

    Seen a few people asking online, but not many people have followed through with feedback.

    Was supposed to be a like for like installation, but there seems to be variation in lengths of branch etc
     

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  3. Hugh Jaleak

    Hugh Jaleak

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    Either option would be fine. If using Pan connector option, fit an Anti Vac trap to the Basin, this will ensure no issue with trap being pulled when WC is flushed.
     
  4. DIYAmelia

    DIYAmelia

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    Thank you. The basin waste shown in photo (just above middle of near horizontal/slightly descending 110 mm wc soil branch) will not use a pan connector branch/junction. The basin joins half way between WC and the stack vent (near horizontal 110 branch, which is about 1m 20cm across in length. Would this still require additional piping, IE anti vac?

    Would this sit on outside vertically? Regs show a vent pipe which needs to be same or higher than max fill height of basin.

    I had this built up to roofline but when I put branch across to WC it was clear the branch could not cope with steepness of angle. A spare 110 stack soil vertical pipe in photo is 10cm longer and doesn't strain the branch joint. It allows the minimum 18mm fall per 1m horizontal length of branch . About 25mm per metre at mo.
    Then the raised height of the vertical 110 soil revealed that the top of branch was too high by 3cm to allow basin waste to join from side using strap on boss.

    The stack vent is of course not yet built up in photo to full height (90cm) above top of windows on upper floor.
    Thoughts appreciated
     
  5. DIYAmelia

    DIYAmelia

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    Web search anti vac.
    They are on bottle trap, u bend about one inch or so high.

    I guess gurgling will be an issue unless I pipe basin waste into vertical stack vent. I was going for chrome plated brass bottle trap on basin waste (no anti vac).
     
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  7. DIYAmelia

    DIYAmelia

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    112.5 degree branch tee needed , which is what I had previously, but company does not supply
     
  8. Hugh Jaleak

    Hugh Jaleak

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    You can connect the waste as shown in your photo without using an Anti Vac trap, outflow from the WC is unlikely to fill the 110mm pipe sufficient to cause a vacuum behind it. Pan connectors are slightly constricted to accommodate the sealing fins which need to fit snugly inside the soil pipe, so any connection to a boss could be subjected to vacuum when the WC is flushed.

    If using an Air Admittance Valve (AAV), this needs to be sited above the spillover level of the highest appliance, (normally the basin), but if you have an external stack, I would recommend you continue up to eaves level and vent it to atmosphere if possible.

    A picture from further back, showing exactly what you're hoping to achieve may help us to advise further, not sure exactly what the issue is regarding the 112.5 ° tee.
     
  9. DIYAmelia

    DIYAmelia

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    Current branch supplied is 92.5 Deg. I had something previously allowing more fall. After drawing different lines on card card using protractor and overlaying on wall, it looks like 112.5 Deg branch is too steep. A 104 Deg branch is on order. Trims at Wakefield could not supply but instead of paying £9 I am paying £38. Small price to pay for no vacuum noises over next few decades though.

    I am venting to above eaves, no AAV.
    I considered an external AAV to tidy up roofline but against regs and one in loft I have blocked up causing gurgling noises.

    I will be sorted once I get my new branch.

    Photo shows old soil pipe setup.

    Th IMG_20201009_161510_2.jpg IMG_20201009_161510_2.jpg anks
     
  10. Hugh Jaleak

    Hugh Jaleak

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    2.5° allows for a sensible fall on the 'horizontal' run, (1:40 is the rule of thumb), anything steeper isn't strictly necessary. If anything, a shallower fall may help, the faster the discharge leaves the WC, the more chance you have of it pulling the air behind it and causing other issues.

    I'd also advise checking that other waste entering from the R/H side, it should be a minimum of 200mm below the centre of the WC branch to avoid crossflow, i.e. discharge from the WC going into the waste and blocking it.
     
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