Waste Pipe Vent or No?

[noseall]

So we are achieving 1/60 on the foul drain line. Just shy of 17mm fall per metre when measured.

Perfect.

By the looks of it, you can be allowed to have less so that is reassuring.

Correct, as long as when its really shallow, the pipes are laid perfectly, i.e. no dips etc.

Although I've noticed some residual water does sit at the bottom of the plastic inspection chambers in the main through channel - is this normal?

Yeah it can be. Just make sure that when you concrete under the chambers (essential), try and give them a little kick at the high end.

What is annoying about these plastic inspection chambers is that whilst the main inlet is low, the rest of the branches are about 2" higher.

I feel your pain. We try and use the bigger 450mm chamber bases, for that very reason.

Having said that, we don't want th gradient to be too steep since that can be as bad as not enough (water flows faster than logs etc).

Myth.

 

[James Davis]

Nose,

My builder has bedded the chamber bases on pea gravel (beneath which is clay ground). Are you saying concrete is definitely a must?

Ps. These chambers are the big 450mm ones and the branches are all higher than the main inlet and outlet.

 

[noseall]

Nose,

My builder has bedded the chamber bases on pea gravel (beneath which is clay ground). Are you saying concrete is definitely a must?

Yes!

Ps. These chambers are the big 450mm ones and the branches are all higher than the main inlet and outlet.

The ones we use are all on the same level i.e. the through channel and the inlets.

 

[James Davis]

Yes!

The ones we use are all on the same level i.e. the through channel and the inlets.

Don't suppose you have a link? I can't find one on Google

 

[Ivor Windybottom]

Level invert chambers are available but they really should be a last resort. I've got one and wish I didn't have. With a standard one, as long as the centre channel gets used regularly it will stay clear. The level invert ones can (and do) back up into all the branches on every flush. It will only be clear after fresh water has run down all branches, which is never in reality.

But they're a problem solver if there's no other option - I had fixed start and end points and needed to lengthen the run to reach a new sewage treatment plant on the way out, so I had the minimum 1 in 80 with nothing left over. I can confirm that 1 in 80 all works absolutely fine IF as said above, everything is meticulously laid with great care. Get a gradient level, definitely concrete all chambers. I concreted most pipes too, to ensure they didn't sag and to protect from tree roots. If concreting pipes then put movement joints in with a slab of polystrene foam every 3m or so.

If you're doing drainage for the first time I'd recommend reading the building regs I linked carefully from start to finish as I did before starting. It's actually really well written and all makes sense. You'll know more than some white van driving specialists by the end of it.

 

[noseall]

Don't suppose you have a link? I can't find one on Google

Slightly misleading regards the invert levels - the 450mm side inlets are offset from the through channel, but a lot less than the bonkers 300mm ones.

 

[Hugh Jaleak]

This 1.3m depth... you can see the open ended pipe the toilet will connect to, where is the lowest point counted as - the horizontal run of orange pipe or the chamber it is going to? Why is 1.3m important, what would 1.5m cause?

The 1.3m rule is in Part H of the Building Regs and something that's stuck in my mind since College days, (don't ask why, as I don't know!) I suspect it may be due to the height the waste is falling from in an unventilated run, a stack would be higher, but should have a longer radius Rest bend at the bottom, and either be open to atmosphere or have an Air Admittance Valve at the top.

Fall has always been pretty critical, you want a 'Self Cleansing Velocity' in a drain. Although I think this may have been more important with the old stoneware runs, which had a lot more joints, 'Too shallow and the liquid will trickle away leaving the solids behind. Too steep and the liquid will run away, again leaving the solids behind.' Former yes, but I've seen some ridiculous gradients on new builds, and they don't block.

 

[James Davis]

The 1.3m rule is in Part H of the Building Regs and something that's stuck in my mind since College days, (don't ask why, as I don't know!) I suspect it may be due to the height the waste is falling from in an unventilated run, a stack would be higher, but should have a longer radius Rest bend at the bottom, and either be open to atmosphere or have an Air Admittance Valve at the top.

I wonder if it is to do with preventing a vacuum as the waste travels down through the pipe? 1.3m possibly being the maximum vertical fall after which water will start getting sucked out of toilet and sink traps? Basically because waste matter filling the pipe pushes the air ahead of it and opens up a vacuum behind it. A horizontal run then resulting in an air gap above the waste again as it goes through the pipe.

So the maximum 1.3m depth and maximum 6m (to a vent) requirements work together to ensure there is enough air (or free air movement, push pull) available in the system to prevent significant vacuums occuring and odours building up. I'm guessing here but seems reasonable.

In my case, the bottom of the new toilet will be less than 1.3m above the bottom of the drain, the vertical drop in the pipe being more like 0.5m, and the nearest vent stack is just short of 7m measured by the run of pipes. So I will take the risk on using a stub stack without a vent to keep it as unintrusive as possible. Worst case scenario I'll have to add one later.

 

[noseall]

I wonder if it is to do with preventing a vacuum as the waste travels down through the pipe? 1.3m possibly being the maximum vertical fall after which water will start getting sucked out of toilet and sink traps? Basically because waste matter filling the pipe pushes the air ahead of it and opens up a vacuum behind it. A horizontal run then resulting in an air gap above the waste again as it goes through the pipe.

So the maximum 1.3m depth and maximum 6m (to a vent) requirements work together to ensure there is enough air (or free air movement, push pull) available in the system to prevent significant vacuums occuring and odours building up. I'm guessing here but seems reasonable.

In my case, the bottom of the new toilet will be less than 1.3m above the bottom of the drain, the vertical drop in the pipe being more like 0.5m, and the nearest vent stack is just short of 7m measured by the run of pipes. So I will take the risk on using a stub stack without a vent to keep it as unintrusive as possible. Worst case scenario I'll have to add one later.

There is no maximum fall other than causing splashes in an IC.

 

[James Davis]

We are talking about max fall, or depth, without a vent.

 

[robinbanks]

You don't want the stub stack inside and you don't want it outside.....

Might have to hide it in the wall then.

Or fit a waterless trap to the sink and have done with it

 

[noseall]

Might have to bury it in the wall then

I've seen that too whereby they deliberately located the SVP within the inner leaf.