Foul drainage under slab

[BenGillyHills]

1 hour ago, saveasteading said:

Thanks for the info.

It's all a bit odd, reinventing the wheel,  and I don't want to get involved. My principle still applies. Keep it simple with bends outside the building.

 

You seem to have a sympathetic bco so keep asking them

 

I hear you. The foundations are what they are at this point and BCO is happy but the drainage needs work..I’m going to focus on getting the drainage right within the limitations of the site. If it can’t work, it can’t work and a drastic change may be necessary, but at this point I’m going to plug away with amending the layout and trying different ideas until it truly is a lost cause.

[Oz07]

That's good to my eyes. If possible where that 110mm pipe comes up for the basin in the far corner can you build an accessible boxing then you could have an access plug into your pipework and rodding access in the unlikely event it was to block. Otherwise you can keep taking the pipe out thru the building on that opposite corner. Will it be high enough to clear the trench concrete by then? Then put external rodding eye. There is an argument to say keep the shower on its own separate run into the manhole then you have no y branch down stream from toilet. I think you'll be fine though. You could even cock the y junction a bit so its not flat and the branch to the shower is sticking up a bit, then immediately put a 15deg fitting on to take the pipe back level. Should give you a small stepped invert. If you've seen a flush invert manhole its really no different to a flat junction and the man holes don't just spontaneously block up. 

 

Where is the resident plumber @Nickfromwales?

[Oz07]

Eliminate the 45 bend after the y branch just position the y so you are coming straight up with a 90 possibly with a short straight stub of pipe between them

[Nickfromwales]

15 hours ago, Oz07 said:

Where is the resident plumber @Nickfromwales?

Doing some carpentry, firing airtightness membranes, and fitting MVHR of course lol. Slight bit of plumbing involved too   

 

The BCO needs to have input here, and if they are pragmatic they’ll just ask for rodding access at the WC, or at worst the OP will need to carry that run on to outside and fit a rodding plate at the level of the hard standing.

 

Usually, from the external chamber, the rules say a straight run with clear line of sight to the rest bend rising to any WC, or any that involve solids (such as a kitchen sink). 
 

As there’s a Y branch, then a 135° bend, then the rising rest bend at the WC, you cannot rod to that rest bend from outside, are there’s the issue with this arrangement.

 

If the Y branch + 135 + rest bend can rise in the corner of the room, boxed in, and there’s a T branch there that has a rodding eye / cap in the top, and then the branch runs horizontally to pick up the WC, that would suffice.

 

No need for a stub stack and an AAV, as the inverts don’t make air admittance an issue here; that means the boxing in can all be low level. 
 

What happens to the pipe at the end of the run? Just collecting a basin, and then going up to roof level to function as an SVP. If so, any possible air admittance is provided there, but could also be done with an anti-siphon basin trap, if the BCO insists on it only! 

[BenGillyHills]

Thanks @Nickfromwales @Oz07,

 

Really appreciate all the knowledge.

 

Before your responses came in, I got cold feet about this layout and came up with what I believe is an improvement. But I’d be keen to know which of the two you think is the better. 
 

A - (with the changes you described)

 

or 

 

B - (If necessary, I would reluctantly put a chamber inside the building where the long radius 45 is, just before pipe exits the building)

 

On this one there would also be a mini stack in the boxing behind the basin with rodding access screw cap at the top and a vertical Y with AAV. Also another vertical Y with 32mm inlet for basin waste. Boxing would be high-level anyway so could easily accommodate this, but from your comments AAV might not be necessary.

 

WC could also have rodding access on vertical coming out of concrete. (Not sure if that’s allowed or necessary).

 

 

I’m planning to go ahead and install one of these options next week then invite BCO out. I figure if it’s already in the ground and visible, we can make it work with slight amendments. I’m reluctant to get him out with nothing to show in case he sends the plan in another, more costly direction!

 

 

[saveasteading]

@BenGillyHills

Have you calculated the falls?

[BenGillyHills]

9 minutes ago, saveasteading said:

@BenGillyHills

Have you calculated the falls?

No, I’m going to do that next, but there is plenty of height to play with as where the pipe is exiting the building is around 600mm lower than the underside of where the concrete slab will be. The drains being connected into are also significantly lower as the whole property is sloped in that direction.

Edited Saturday at 12:59 by BenGillyHills

[saveasteading]

37 minutes ago, BenGillyHills said:

plenty of height to play with as where the pipe is exiting the

You should work it out before going any further. There are maximum as well as minimum falls. And to get a depth that satisfies the regulations but minimises excavation.

[Russell griffiths]

still confused. 
if your internal finished floor is 600mm higher than the concrete foundation, you will want external ground level 150 below damp course level or ffh, so your external ground level needs to come up 200mm at least, so won’t that allow you to route your pipes out anywhere. 

[Oz07]

Just do plan A I bet the BCO approves. Plan B looks messy to me

[Oz07]

24 minutes ago, saveasteading said:

You should work it out before going any further. There are maximum as well as minimum falls. And to get a depth that satisfies the regulations but minimises excavation.

There aren't maximum falls anymore as I understand it. PVC pipe did away with that

[gravelrash]

min 1 in100 and max 1 in 40 slope is there to save you having turds sat in your pipe regardless of type of pipe

[BenGillyHills]

51 minutes ago, Russell griffiths said:

still confused. 
if your internal finished floor is 600mm higher than the concrete foundation, you will want external ground level 150 below damp course level or ffh, so your external ground level needs to come up 200mm at least, so won’t that allow you to route your pipes out anywhere.

 

The 600mm (maybe less now I’m looking at it, but plenty!) height difference is in relation to the section of stepped down trenches where the concrete foundation is lower. That’s why I’m so keen to run the pipe to this area. 
 

By doing this I will be achieving 150mm ground below DPC and not be bringing the external ground level up with my BCO approved foundation/ground floor make-up. 

Edited Saturday at 14:41 by BenGillyHills

[BenGillyHills]

34 minutes ago, Oz07 said:

Just do plan A I bet the BCO approves. Plan B looks messy to me

Wish I hadn’t ordered all materials for Plan B this morning 🤦‍♂️. I can adapt, but do you think Plan B is compliant? @Nickfromwales do you have a preference?

Edited Saturday at 14:36 by BenGillyHills

[saveasteading]

55 minutes ago, Oz07 said:

aren't maximum falls anymore

You're right, my apologies. There should be though, and there certainly are on main sewers and i would apply it for bigger buildings.  I guess it doesn't matter much to society.

 

I wonder why they dropped the regulation.

 

Let's just say, it's a good idea to use a steady gradient so that it all flows nicely.

[Oz07]

1 hour ago, gravelrash said:

min 1 in100 and max 1 in 40 slope is there to save you having turds sat in your pipe regardless of type of pipe

min 1 in 80 with 4" pipe and at least a loo plumbed into it i think. I'd be wary of going any less on 4" pipe. Has to be steeper if it's not getting as much flow down.

[Nickfromwales]

5 hours ago, BenGillyHills said:

Wish I hadn’t ordered all materials for Plan B this morning 🤦‍♂️. I can adapt, but do you think Plan B is compliant? @Nickfromwales do you have a preference?

I don't have a preference here, so-to-speak, as it needs to be compliant.

Plan B is kosher, just I'd be doing everything I could to not have an IC inside my house. But it's a cabin, and you are where you are, so in reality, as long as you buy a proper screwed gas/water-tight lid IC, then carry on!

[ETC]

Errr……why don’t you move the services to where you can get them out of the building?

Plus:

Connect the WC directly to an IC outside the building.

Connect each appliance to an external GT and then to an IC.

Vent the highest IC.

[BenGillyHills]

42 minutes ago, Nickfromwales said:

I don't have a preference here, so-to-speak, as it needs to be compliant.

Plan B is kosher, just I'd be doing everything I could to not have an IC inside my house. But it's a cabin, and you are where you are, so in reality, as long as you buy a proper screwed gas/water-tight lid IC, then carry on!

Thanks. I agree, don’t want an IC in the house if it can be avoided. If I end up going with option B then the IC will be in the service/boiler room, which has its own external entrance and no access from the main building so I’m not too concerned with it being in there. 

[Nickfromwales]

2 hours ago, BenGillyHills said:

Thanks. I agree, don’t want an IC in the house if it can be avoided. If I end up going with option B then the IC will be in the service/boiler room, which has its own external entrance and no access from the main building so I’m not too concerned with it being in there. 

Carry on then squire. 
 

“so B it” lol.