Routing of waste and Sewer pipes

query on routing waste water pipes..
I have a radon membrane with sub floor over it (100mm). I have ran all the main sewer pipes under the subfloor and they come up from the ground wherever I plan to put a toilet. I have also a few of these in my utility room for waste water. I do not want the waste water pipes from the sinks baths etc etc, to be routed out through the wall and be visable from outside or route out of the first floor to the gables and down. All the sewer pipes on the 1st floor are routed down the interior of the house and out under the subfloor also.
Now my question is as follows. The plan is to run all the 50 mm pipes into the larger 100mm pipes which are up out of the ground (vertical) connect the 50mm pipes into these and then cover over with a 75 mm screed. Prior to the screed I will put down a 50mm kingspan insulation, and will have to cut it around the 50 mm pipes. Or can I cut into the subfloor and sink these pipes into it.???
I am also putting UFH pipes over all of this.
Is it common practice to connect 50mm waste water pipes into the 100 mm sewer pipes, and then screed over.
The other query is that I need to vent the system somewhere. Is this normally vented at the highest point of the sewer system.
I want to install the vent stack through the inside of the house also, through a mushroom slate on the roof, as again I do not want pipes on the exterior of the house. Any ideas how to do this??.
Your experience or input would be much appreciated.

It is indeed common practice to run pipes all over the place but what is common is not always good. I take it that you object to unsightly external gulley traps also.
I would suggest that you ask a local plumber to advise on site.

Thanks Plumber.
So would you consider what I am trying to do as bad practice?
WRT external gulley traps, yes I would prefer not to have these, apart from rainwater ones. I will be getting a local plumber to do this, however I would like to consider my options in advance.
Anyone any ideas.

€25 spent on the Homebond book would be a good investment for you. I think connecting to the 4" pipe underground by the 2" pipe is going to cause you problems with siphoning, a toilet flushed upstairs mayl be able to break the water trap under your sinks if you have a normal seal. You would IMO connect your 2" branch pipes to a gulley trap (finished to path level and therefore ventilated) underground and then have that 4" pipe connect to the main sewer.


You may also have problems with your upstairs 2" pipes in that you will need offsets when making connections to an internal stack and if the offset cannot be achieved you need to fit a ventilation pipe to the sink or bath.