Foul drainage under slab

[BenGillyHills]

I am currently working on a 5 x 11m Annex/Cabin. It will be single storey, one bedroom, timber frame with strip foundations built to comply with UK building regulations. I have a private BC  company on-board. We have the footing poured so the next stage is block work below DPC and services laid under the slab. The project is self design and self build and it’s size and scale is well within my comfort zone although I am not a professional builder. (I’ve done lots of renovations and built smaller cabins)

 

I’ve been doing research to get an idea of rules and regulations for underground drainage, and I can see that a good design and rodding access is vital but there doesn’t seem to be any hard and fast rules about underground bends and direction changes as far as I can tell.

 

can anyone give any feedback of the drainage plan I have come up with?

 

Look forward to hearing anything anyone has to offer.

[Mr Punter]

The long radius horizontal is a no-no.  There are no inspection chambers.  Why not take the pipework outside from the bathroom and run around the building?  That way you can add proper access for inspection and rodding.

[JamesP]

I agree with @Mr Punter. Have 2 runs.

Not a professional but I exited pipework out of the building to avoid long runs within the slab.

Bit of extra external excavation but all accessible.

[BenGillyHills]

Thanks for your helpful comments. The pipe has to exit the building where shown on the diagram as this is the only place where the trenches are deep enough. When it became evident that these trenches would be stepped down, I earmarked this area for pipe to exit the building but never considered the location of the bathroom in relation to it. Some head scratching required…As there will be a service room behind the shower, Initial thoughts to solve the problem would be to put an inspection chamber in the service room, running all bathroom drainage to this point. Then it will be a straight run under slab to the existing exit point. There will need to be a bend here just before the pipe exits, not sure if that’s going to fly but will amend the design accordingly and post back here for more feedback. 

[Mr Punter]

After the pipe crosses the foundation it can immediately drop down, so unless your external finish level is on the foundation you should be able to accommodate this.  At this stage it is not too late to create a channel in the foundation and run the pipework a bit lower.

[BenGillyHills]

Thanks again, this is how the ground floor make-up will be in the area where you were suggesting the pipe could exit (outside bathroom). Do you suggest the 4 inch pipe is channelled through the concrete underneath the course of trench blocks? I haven’t laid trench blocks yet so at this stage the opening could be cut and broken out rather than cored through. Which would be straightforward. Am I interpreting what you’re saying correctly?

[BenGillyHills]

This was the other option I was considering, which includes an inspection chamber within the service room. Although there is a  90° bend before the exit, the access from both inspection chambers is very good so I’m wondering whether this a valid solution.

[Oz07]

Stop having 90s under your slab. Just get the straightest runs you can

[Oz07]

Something like this. You can take thru the opposite wall put a 45 on then rodding eye at ground level. I would say be better if wc comes in with a 90 bend to the invert rather than a swept 90 poking upwards so put a horizontal y in. Make the run inline with basin point and join wc into it with a y. If you cant take shower drain out right where it is on external wall then join with a y just before the drains pass thru wall. Also prob take shower drain out with rodding access. 

 

I'm just thinking on my feet. There are probably better ways

[BenGillyHills]

4 minutes ago, Oz07 said:

Something like this. You can take thru the opposite wall put a 45 on then rodding eye at ground level. I would say be better if wc comes in with a 90 bend to the invert rather than a swept 90 poking upwards so put a horizontal y in. Make the run inline with basin point and join wc into it with a y. If you cant take shower drain out right where it is on external wall then join with a y just before the drains pass thru wall. Also prob take shower drain out with rodding access. 

 

I'm just thinking on my feet. There are probably better ways

Thanks, I appreciate the thought. I’m going to digest what you said and see if I can improve the layout. I think I need to establish if I’m able to break through my foundation concrete to run pipe the in which case I will make logical exits near the bathroom and run pipe outside the building accordingly. I’ve made a rod for my back by limiting where I can easily

exit pipe through foundations.