BenGillyHills

I’m self-building an annex and looking for some advice from those in the know… I had originally intended to exit foul drainage pipes through a section where the foundations are stepped down (and therefore plenty of room with three courses of trench blocks to go through) but hadn’t considered that this section is a long way away from the bathroom. Can I do as the diagram shows and channel through the already-cast concrete footing as well go through the trench block course as shown? I would install a lintel above. Once drains are installed and BC are happy, would I then concrete-in the exit opening? what is best practice for finishing a lintel opening like this? Any advice appreciated. Ben

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.

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.

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?

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.

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.