Soil stack manifold and syphonage

[cdbe]

Hi, please see attached drawing (the top half is the elevation, the bottom half is the plan view) - I want to install new drainage along the lines of that shown. I can't figure out whether it's necessary to vent the stack (which will be in the middle of the house)? I am considering using a 4 way manifold on the ground floor (for 1st floor shower and basin, ground floor - basin, washing machine, kitchen sink and dishwasher).

According to the manufacurers the manifolds "help prevent" syphonage but I don't know how successfully. I could fit a durgo on top of the new stack if I had to or run it up to the roof through the loft but space is tight.

Thanks for any advice.

 

[Newboy]

Joining two appliances into one run should be avoided (first floor basin & shower) - run these to the stack at first floor level with boss connections.
A manifold connection at ground floor would be ok to connect the three ground floor wastes.

With two pans and five other appliances an AAV is a must - I'd be inclined to install a vented stack.

Rest bend at the base of the new stack and an IC at the new underground connection.

Building regs approval required for this work.

 

[Hugh Jaleak]

+1 for that advice. Ideally the vent needs to be at the head of the drainage system, so your new stack needs to be vented. You also need to check levels of existing drainage, and make sure you can get required falls. The Building Regs do not allow any connections into a stack less than 450mm above the invert of the outgoing drain.

For reference if you need them, https://www.planningportal.co.uk/in...ments/71/part_h_-_drainage_and_waste_disposal

 

[John D v2.0]

that's actually topologically quite similar to our layout, although ours is slightly simpler.

with the existing open ventilation you state, you will also need an AAV at the top of the 110mm internal stack, plus the basin/shower stack that runs in parallel will also need an aav and will need to be 50mm diameter pipe minimum..

That 4 way manifold will need a rest bend or two 45 degree bends under to direct the falling waste along the horizontal pipe. Ideally it should also be suitable for mounting so close to the rest bend.

We didn't try to run everything into a manifold due to space behind the wall mounted loo, so I just ran everything other than the loo into a 50mm stack and combined into a 110mm y branch on the horizontal drain after the rest bend.

 

[cdbe]

Thanks all, great advice. I will amend the design to run the upstairs waste's into a boss - handy because I forgot the dishwasher will need a space in the manifold. I will find the space to vent the stack. Good advice about the 2 x 45's as a rest bend is £18 in Wickes!

 

[John D v2.0]

Just a pointer that with rest bends they have a leg for support built in, if you're using a couple of 45s be sure to support them properly. You don't want your pipe to come apart after a big flush

 

[Newboy]

Good advice about the 2 x 45's as a rest bend is £18 in Wickes!

and a 45° is £9.19! (in Wickes)

Use a rest bend - that's what it's for!

 

[John D v2.0]

and a 45° is £9.19! (in Wickes)

Use a rest bend - that's what it's for!

don't go to wickes to save money
use toolstation same company and 5.38 each.
https://www.toolstation.com/shop/Roofing+&+Drainage/d250/110mm+Underground/sd2868/Single+Socket+Bend+110mm/p79259

rest bend is 14.37
https://www.toolstation.com/shop/Roofing+&+Drainage/d250/110mm+Underground/sd2868/Rest+Bend+110mm/p12565

tbh you're not doing it to save money, in my case there was no space at the apex of the bend due to a wall plate and sleeper wall, so I had no choice.

 

[cdbe]

True. It's just that I had a couple of 45's. However with all the other stuff I need I'll probably have enough to qualify for free delivery with Plastics Express so I'll use the proper kit.